Adding upstream version 2.1.2.

Signed-off-by: Daniel Baumann <daniel@debian.org>

.github/workflows/ci.yml

@@ -0,0 +1,33 @@
+name: "Continuous Integration"
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [ main ]
+    paths: [ "*.go" ]
+  pull_request:
+    branches: [ main ]
+    paths: [ "*.go" ]
+
+jobs:
+  ci:
+    name: "Tests"
+    runs-on: ubuntu-latest
+
+    env:
+      GOOS: "linux"
+      GOARCH: "amd64"
+      GO111MODULE: "on"
+      CGO_ENABLED: "0"
+
+    steps:
+    - name: Set up Go
+      uses: actions/setup-go@v3
+      with:
+        go-version: 1.21
+
+    - name: Check out go-incr
+      uses: actions/checkout@v3
+
+    - name: Run all tests
+      run: go test ./...

.gitignore

@@ -0,0 +1,20 @@
+# Binaries for programs and plugins
+*.exe
+*.dll
+*.so
+*.dylib
+
+# Test binary, build with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736
+.glide/
+
+# Other
+.vscode
+.DS_Store
+coverage.html
+.idea

COVERAGE

@@ -0,0 +1 @@
+29.02

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2016 William Charczuk.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Makefile

@@ -0,0 +1,10 @@
+all: new-install test
+
+new-install:
+	@go get -v -u ./...
+
+generate:
+	@go generate ./...
+
+test:
+	@go test ./...

PROFANITY_RULES.yml

@@ -0,0 +1,4 @@
+go-sdk:
+  excludeFiles: [ "*_test.go" ]
+  importsContain: [ github.com/blend/go-sdk/* ]
+  description: "please don't use go-sdk in this repo"

README.md

@@ -0,0 +1,95 @@
+go-chart
+========
+[![Continuous Integration](https://github.com/wcharczuk/go-chart/actions/workflows/ci.yml/badge.svg)](https://github.com/wcharczuk/go-chart/actions/workflows/ci.yml) [![Go Report Card](https://goreportcard.com/badge/github.com/wcharczuk/go-chart)](https://goreportcard.com/report/github.com/wcharczuk/go-chart)
+
+Package `chart` is a very simple golang native charting library that supports timeseries and continuous line charts.
+
+Master should now be on the v3.x codebase, which overhauls the api significantly. Per usual, see `examples` for more information.
+
+# Installation
+
+To install `chart` run the following:
+
+```bash
+> go get github.com/wcharczuk/go-chart/v2@latest
+```
+
+Most of the components are interchangeable so feel free to crib whatever you want.
+
+# Output Examples
+
+Spark Lines:
+
+![](https://raw.githubusercontent.com/wcharczuk/go-chart/master/_images/tvix_ltm.png)
+
+Single axis:
+
+![](https://raw.githubusercontent.com/wcharczuk/go-chart/master/_images/goog_ltm.png)
+
+Two axis:
+
+![](https://raw.githubusercontent.com/wcharczuk/go-chart/master/_images/two_axis.png)
+
+# Other Chart Types
+
+Pie Chart:
+
+![](https://raw.githubusercontent.com/wcharczuk/go-chart/master/_images/pie_chart.png)
+
+The code for this chart can be found in `examples/pie_chart/main.go`.
+
+Stacked Bar:
+
+![](https://raw.githubusercontent.com/wcharczuk/go-chart/master/_images/stacked_bar.png)
+
+The code for this chart can be found in `examples/stacked_bar/main.go`.
+
+# Code Examples
+
+Actual chart configurations and examples can be found in the `./examples/` directory. They are simple CLI programs that write to `output.png` (they are also updated with `go generate`.
+
+# Usage
+
+Everything starts with the `chart.Chart` object. The bare minimum to draw a chart would be the following:
+
+```golang
+
+import (
+    ...
+    "bytes"
+    ...
+    "github.com/wcharczuk/go-chart/v2" //exposes "chart"
+)
+
+graph := chart.Chart{
+    Series: []chart.Series{
+        chart.ContinuousSeries{
+            XValues: []float64{1.0, 2.0, 3.0, 4.0},
+            YValues: []float64{1.0, 2.0, 3.0, 4.0},
+        },
+    },
+}
+
+buffer := bytes.NewBuffer([]byte{})
+err := graph.Render(chart.PNG, buffer)
+```
+
+Explanation of the above: A `chart` can have many `Series`, a `Series` is a collection of things that need to be drawn according to the X range and the Y range(s).
+
+Here, we have a single series with x range values as float64s, rendered to a PNG. Note; we can pass any type of `io.Writer` into `Render(...)`, meaning that we can render the chart to a file or a resonse or anything else that implements `io.Writer`.
+
+# API Overview
+
+Everything on the `chart.Chart` object has defaults that can be overriden. Whenever a developer sets a property on the chart object, it is to be assumed that value will be used instead of the default.
+
+The best way to see the api in action is to look at the examples in the `./_examples/` directory.
+
+# Design Philosophy
+
+I wanted to make a charting library that used only native golang, that could be stood up on a server (i.e. it had built in fonts).
+
+The goal with the API itself is to have the "zero value be useful", and to require the user to not code more than they absolutely needed.
+
+# Contributions
+
+Contributions are welcome though this library is in a holding pattern for the forseable future.

_colors/colors_extended.txt

@@ -0,0 +1,147 @@
+aliceblue 	#f0f8ff 	240,248,255
+antiquewhite 	#faebd7 	250,235,215
+aqua 	#00ffff 	0,255,255
+aquamarine 	#7fffd4 	127,255,212
+azure 	#f0ffff 	240,255,255
+beige 	#f5f5dc 	245,245,220
+bisque 	#ffe4c4 	255,228,196
+black 	#000000 	0,0,0
+blanchedalmond 	#ffebcd 	255,235,205
+blue 	#0000ff 	0,0,255
+blueviolet 	#8a2be2 	138,43,226
+brown 	#a52a2a 	165,42,42
+burlywood 	#deb887 	222,184,135
+cadetblue 	#5f9ea0 	95,158,160
+chartreuse 	#7fff00 	127,255,0
+chocolate 	#d2691e 	210,105,30
+coral 	#ff7f50 	255,127,80
+cornflowerblue 	#6495ed 	100,149,237
+cornsilk 	#fff8dc 	255,248,220
+crimson 	#dc143c 	220,20,60
+cyan 	#00ffff 	0,255,255
+darkblue 	#00008b 	0,0,139
+darkcyan 	#008b8b 	0,139,139
+darkgoldenrod 	#b8860b 	184,134,11
+darkgray 	#a9a9a9 	169,169,169
+darkgreen 	#006400 	0,100,0
+darkgrey 	#a9a9a9 	169,169,169
+darkkhaki 	#bdb76b 	189,183,107
+darkmagenta 	#8b008b 	139,0,139
+darkolivegreen 	#556b2f 	85,107,47
+darkorange 	#ff8c00 	255,140,0
+darkorchid 	#9932cc 	153,50,204
+darkred 	#8b0000 	139,0,0
+darksalmon 	#e9967a 	233,150,122
+darkseagreen 	#8fbc8f 	143,188,143
+darkslateblue 	#483d8b 	72,61,139
+darkslategray 	#2f4f4f 	47,79,79
+darkslategrey 	#2f4f4f 	47,79,79
+darkturquoise 	#00ced1 	0,206,209
+darkviolet 	#9400d3 	148,0,211
+deeppink 	#ff1493 	255,20,147
+deepskyblue 	#00bfff 	0,191,255
+dimgray 	#696969 	105,105,105
+dimgrey 	#696969 	105,105,105
+dodgerblue 	#1e90ff 	30,144,255
+firebrick 	#b22222 	178,34,34
+floralwhite 	#fffaf0 	255,250,240
+forestgreen 	#228b22 	34,139,34
+fuchsia 	#ff00ff 	255,0,255
+gainsboro 	#dcdcdc 	220,220,220
+ghostwhite 	#f8f8ff 	248,248,255
+gold 	#ffd700 	255,215,0
+goldenrod 	#daa520 	218,165,32
+gray 	#808080 	128,128,128
+green 	#008000 	0,128,0
+greenyellow 	#adff2f 	173,255,47
+grey 	#808080 	128,128,128
+honeydew 	#f0fff0 	240,255,240
+hotpink 	#ff69b4 	255,105,180
+indianred 	#cd5c5c 	205,92,92
+indigo 	#4b0082 	75,0,130
+ivory 	#fffff0 	255,255,240
+khaki 	#f0e68c 	240,230,140
+lavender 	#e6e6fa 	230,230,250
+lavenderblush 	#fff0f5 	255,240,245
+lawngreen 	#7cfc00 	124,252,0
+lemonchiffon 	#fffacd 	255,250,205
+lightblue 	#add8e6 	173,216,230
+lightcoral 	#f08080 	240,128,128
+lightcyan 	#e0ffff 	224,255,255
+lightgoldenrodyellow 	#fafad2 	250,250,210
+lightgray 	#d3d3d3 	211,211,211
+lightgreen 	#90ee90 	144,238,144
+lightgrey 	#d3d3d3 	211,211,211
+lightpink 	#ffb6c1 	255,182,193
+lightsalmon 	#ffa07a 	255,160,122
+lightseagreen 	#20b2aa 	32,178,170
+lightskyblue 	#87cefa 	135,206,250
+lightslategray 	#778899 	119,136,153
+lightslategrey 	#778899 	119,136,153
+lightsteelblue 	#b0c4de 	176,196,222
+lightyellow 	#ffffe0 	255,255,224
+lime 	#00ff00 	0,255,0
+limegreen 	#32cd32 	50,205,50
+linen 	#faf0e6 	250,240,230
+magenta 	#ff00ff 	255,0,255
+maroon 	#800000 	128,0,0
+mediumaquamarine 	#66cdaa 	102,205,170
+mediumblue 	#0000cd 	0,0,205
+mediumorchid 	#ba55d3 	186,85,211
+mediumpurple 	#9370db 	147,112,219
+mediumseagreen 	#3cb371 	60,179,113
+mediumslateblue 	#7b68ee 	123,104,238
+mediumspringgreen 	#00fa9a 	0,250,154
+mediumturquoise 	#48d1cc 	72,209,204
+mediumvioletred 	#c71585 	199,21,133
+midnightblue 	#191970 	25,25,112
+mintcream 	#f5fffa 	245,255,250
+mistyrose 	#ffe4e1 	255,228,225
+moccasin 	#ffe4b5 	255,228,181
+navajowhite 	#ffdead 	255,222,173
+navy 	#000080 	0,0,128
+oldlace 	#fdf5e6 	253,245,230
+olive 	#808000 	128,128,0
+olivedrab 	#6b8e23 	107,142,35
+orange 	#ffa500 	255,165,0
+orangered 	#ff4500 	255,69,0
+orchid 	#da70d6 	218,112,214
+palegoldenrod 	#eee8aa 	238,232,170
+palegreen 	#98fb98 	152,251,152
+paleturquoise 	#afeeee 	175,238,238
+palevioletred 	#db7093 	219,112,147
+papayawhip 	#ffefd5 	255,239,213
+peachpuff 	#ffdab9 	255,218,185
+peru 	#cd853f 	205,133,63
+pink 	#ffc0cb 	255,192,203
+plum 	#dda0dd 	221,160,221
+powderblue 	#b0e0e6 	176,224,230
+purple 	#800080 	128,0,128
+red 	#ff0000 	255,0,0
+rosybrown 	#bc8f8f 	188,143,143
+royalblue 	#4169e1 	65,105,225
+saddlebrown 	#8b4513 	139,69,19
+salmon 	#fa8072 	250,128,114
+sandybrown 	#f4a460 	244,164,96
+seagreen 	#2e8b57 	46,139,87
+seashell 	#fff5ee 	255,245,238
+sienna 	#a0522d 	160,82,45
+silver 	#c0c0c0 	192,192,192
+skyblue 	#87ceeb 	135,206,235
+slateblue 	#6a5acd 	106,90,205
+slategray 	#708090 	112,128,144
+slategrey 	#708090 	112,128,144
+snow 	#fffafa 	255,250,250
+springgreen 	#00ff7f 	0,255,127
+steelblue 	#4682b4 	70,130,180
+tan 	#d2b48c 	210,180,140
+teal 	#008080 	0,128,128
+thistle 	#d8bfd8 	216,191,216
+tomato 	#ff6347 	255,99,71
+turquoise 	#40e0d0 	64,224,208
+violet 	#ee82ee 	238,130,238
+wheat 	#f5deb3 	245,222,179
+white 	#ffffff 	255,255,255
+whitesmoke 	#f5f5f5 	245,245,245
+yellow 	#ffff00 	255,255,0
+yellowgreen 	#9acd32 	154,205,50

annotation_series.go

@@ -0,0 +1,91 @@
+package chart
+
+import (
+	"fmt"
+	"math"
+)
+
+// Interface Assertions.
+var (
+	_ Series = (*AnnotationSeries)(nil)
+)
+
+// AnnotationSeries is a series of labels on the chart.
+type AnnotationSeries struct {
+	Name        string
+	Style       Style
+	YAxis       YAxisType
+	Annotations []Value2
+}
+
+// GetName returns the name of the time series.
+func (as AnnotationSeries) GetName() string {
+	return as.Name
+}
+
+// GetStyle returns the line style.
+func (as AnnotationSeries) GetStyle() Style {
+	return as.Style
+}
+
+// GetYAxis returns which YAxis the series draws on.
+func (as AnnotationSeries) GetYAxis() YAxisType {
+	return as.YAxis
+}
+
+func (as AnnotationSeries) annotationStyleDefaults(defaults Style) Style {
+	return Style{
+		FontColor:   DefaultTextColor,
+		Font:        defaults.Font,
+		FillColor:   DefaultAnnotationFillColor,
+		FontSize:    DefaultAnnotationFontSize,
+		StrokeColor: defaults.StrokeColor,
+		StrokeWidth: defaults.StrokeWidth,
+		Padding:     DefaultAnnotationPadding,
+	}
+}
+
+// Measure returns a bounds box of the series.
+func (as AnnotationSeries) Measure(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) Box {
+	box := Box{
+		Top:    math.MaxInt32,
+		Left:   math.MaxInt32,
+		Right:  0,
+		Bottom: 0,
+	}
+	if !as.Style.Hidden {
+		seriesStyle := as.Style.InheritFrom(as.annotationStyleDefaults(defaults))
+		for _, a := range as.Annotations {
+			style := a.Style.InheritFrom(seriesStyle)
+			lx := canvasBox.Left + xrange.Translate(a.XValue)
+			ly := canvasBox.Bottom - yrange.Translate(a.YValue)
+			ab := Draw.MeasureAnnotation(r, canvasBox, style, lx, ly, a.Label)
+			box.Top = MinInt(box.Top, ab.Top)
+			box.Left = MinInt(box.Left, ab.Left)
+			box.Right = MaxInt(box.Right, ab.Right)
+			box.Bottom = MaxInt(box.Bottom, ab.Bottom)
+		}
+	}
+	return box
+}
+
+// Render draws the series.
+func (as AnnotationSeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) {
+	if !as.Style.Hidden {
+		seriesStyle := as.Style.InheritFrom(as.annotationStyleDefaults(defaults))
+		for _, a := range as.Annotations {
+			style := a.Style.InheritFrom(seriesStyle)
+			lx := canvasBox.Left + xrange.Translate(a.XValue)
+			ly := canvasBox.Bottom - yrange.Translate(a.YValue)
+			Draw.Annotation(r, canvasBox, style, lx, ly, a.Label)
+		}
+	}
+}
+
+// Validate validates the series.
+func (as AnnotationSeries) Validate() error {
+	if len(as.Annotations) == 0 {
+		return fmt.Errorf("annotation series requires annotations to be set and not empty")
+	}
+	return nil
+}

annotation_series_test.go

@@ -0,0 +1,115 @@
+package chart
+
+import (
+	"image/color"
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/drawing"
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestAnnotationSeriesMeasure(t *testing.T) {
+	// replaced new assertions helper
+
+	as := AnnotationSeries{
+		Annotations: []Value2{
+			{XValue: 1.0, YValue: 1.0, Label: "1.0"},
+			{XValue: 2.0, YValue: 2.0, Label: "2.0"},
+			{XValue: 3.0, YValue: 3.0, Label: "3.0"},
+			{XValue: 4.0, YValue: 4.0, Label: "4.0"},
+		},
+	}
+
+	r, err := PNG(110, 110)
+	testutil.AssertNil(t, err)
+
+	f, err := GetDefaultFont()
+	testutil.AssertNil(t, err)
+
+	xrange := &ContinuousRange{
+		Min:    1.0,
+		Max:    4.0,
+		Domain: 100,
+	}
+	yrange := &ContinuousRange{
+		Min:    1.0,
+		Max:    4.0,
+		Domain: 100,
+	}
+
+	cb := Box{
+		Top:    5,
+		Left:   5,
+		Right:  105,
+		Bottom: 105,
+	}
+	sd := Style{
+		FontSize: 10.0,
+		Font:     f,
+	}
+
+	box := as.Measure(r, cb, xrange, yrange, sd)
+	testutil.AssertFalse(t, box.IsZero())
+	testutil.AssertEqual(t, -5.0, box.Top)
+	testutil.AssertEqual(t, 5.0, box.Left)
+	testutil.AssertEqual(t, 146.0, box.Right) //the top,left annotation sticks up 5px and out ~44px.
+	testutil.AssertEqual(t, 115.0, box.Bottom)
+}
+
+func TestAnnotationSeriesRender(t *testing.T) {
+	// replaced new assertions helper
+
+	as := AnnotationSeries{
+		Style: Style{
+			FillColor:   drawing.ColorWhite,
+			StrokeColor: drawing.ColorBlack,
+		},
+		Annotations: []Value2{
+			{XValue: 1.0, YValue: 1.0, Label: "1.0"},
+			{XValue: 2.0, YValue: 2.0, Label: "2.0"},
+			{XValue: 3.0, YValue: 3.0, Label: "3.0"},
+			{XValue: 4.0, YValue: 4.0, Label: "4.0"},
+		},
+	}
+
+	r, err := PNG(110, 110)
+	testutil.AssertNil(t, err)
+
+	f, err := GetDefaultFont()
+	testutil.AssertNil(t, err)
+
+	xrange := &ContinuousRange{
+		Min:    1.0,
+		Max:    4.0,
+		Domain: 100,
+	}
+	yrange := &ContinuousRange{
+		Min:    1.0,
+		Max:    4.0,
+		Domain: 100,
+	}
+
+	cb := Box{
+		Top:    5,
+		Left:   5,
+		Right:  105,
+		Bottom: 105,
+	}
+	sd := Style{
+		FontSize: 10.0,
+		Font:     f,
+	}
+
+	as.Render(r, cb, xrange, yrange, sd)
+
+	rr, isRaster := r.(*rasterRenderer)
+	testutil.AssertTrue(t, isRaster)
+	testutil.AssertNotNil(t, rr)
+
+	c := rr.i.At(38, 70)
+	converted, isRGBA := color.RGBAModel.Convert(c).(color.RGBA)
+	testutil.AssertTrue(t, isRGBA)
+	testutil.AssertEqual(t, 0, converted.R)
+	testutil.AssertEqual(t, 0, converted.G)
+	testutil.AssertEqual(t, 0, converted.B)
+}

array.go

@@ -0,0 +1,24 @@
+package chart
+
+var (
+	_ Sequence = (*Array)(nil)
+)
+
+// NewArray returns a new array from a given set of values.
+// Array implements Sequence, which allows it to be used with the sequence helpers.
+func NewArray(values ...float64) Array {
+	return Array(values)
+}
+
+// Array is a wrapper for an array of floats that implements `ValuesProvider`.
+type Array []float64
+
+// Len returns the value provider length.
+func (a Array) Len() int {
+	return len(a)
+}
+
+// GetValue returns the value at a given index.
+func (a Array) GetValue(index int) float64 {
+	return a[index]
+}

axis.go

@@ -0,0 +1,45 @@
+package chart
+
+// TickPosition is an enumeration of possible tick drawing positions.
+type TickPosition int
+
+const (
+	// TickPositionUnset means to use the default tick position.
+	TickPositionUnset TickPosition = 0
+	// TickPositionBetweenTicks draws the labels for a tick between the previous and current tick.
+	TickPositionBetweenTicks TickPosition = 1
+	// TickPositionUnderTick draws the tick below the tick.
+	TickPositionUnderTick TickPosition = 2
+)
+
+// YAxisType is a type of y-axis; it can either be primary or secondary.
+type YAxisType int
+
+const (
+	// YAxisPrimary is the primary axis.
+	YAxisPrimary YAxisType = 0
+	// YAxisSecondary is the secondary axis.
+	YAxisSecondary YAxisType = 1
+)
+
+// Axis is a chart feature detailing what values happen where.
+type Axis interface {
+	GetName() string
+	SetName(name string)
+
+	GetStyle() Style
+	SetStyle(style Style)
+
+	GetTicks() []Tick
+	GenerateTicks(r Renderer, ra Range, vf ValueFormatter) []Tick
+
+	// GenerateGridLines returns the gridlines for the axis.
+	GetGridLines(ticks []Tick) []GridLine
+
+	// Measure should return an absolute box for the axis.
+	// This is used when auto-fitting the canvas to the background.
+	Measure(r Renderer, canvasBox Box, ra Range, style Style, ticks []Tick) Box
+
+	// Render renders the axis.
+	Render(r Renderer, canvasBox Box, ra Range, style Style, ticks []Tick)
+}

bar_chart.go

@@ -0,0 +1,491 @@
+package chart
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"math"
+
+	"github.com/golang/freetype/truetype"
+)
+
+// BarChart is a chart that draws bars on a range.
+type BarChart struct {
+	Title      string
+	TitleStyle Style
+
+	ColorPalette ColorPalette
+
+	Width  int
+	Height int
+	DPI    float64
+
+	BarWidth int
+
+	Background Style
+	Canvas     Style
+
+	XAxis Style
+	YAxis YAxis
+
+	BarSpacing int
+
+	UseBaseValue bool
+	BaseValue    float64
+
+	Font        *truetype.Font
+	defaultFont *truetype.Font
+
+	Bars     []Value
+	Elements []Renderable
+}
+
+// GetDPI returns the dpi for the chart.
+func (bc BarChart) GetDPI() float64 {
+	if bc.DPI == 0 {
+		return DefaultDPI
+	}
+	return bc.DPI
+}
+
+// GetFont returns the text font.
+func (bc BarChart) GetFont() *truetype.Font {
+	if bc.Font == nil {
+		return bc.defaultFont
+	}
+	return bc.Font
+}
+
+// GetWidth returns the chart width or the default value.
+func (bc BarChart) GetWidth() int {
+	if bc.Width == 0 {
+		return DefaultChartWidth
+	}
+	return bc.Width
+}
+
+// GetHeight returns the chart height or the default value.
+func (bc BarChart) GetHeight() int {
+	if bc.Height == 0 {
+		return DefaultChartHeight
+	}
+	return bc.Height
+}
+
+// GetBarSpacing returns the spacing between bars.
+func (bc BarChart) GetBarSpacing() int {
+	if bc.BarSpacing == 0 {
+		return DefaultBarSpacing
+	}
+	return bc.BarSpacing
+}
+
+// GetBarWidth returns the default bar width.
+func (bc BarChart) GetBarWidth() int {
+	if bc.BarWidth == 0 {
+		return DefaultBarWidth
+	}
+	return bc.BarWidth
+}
+
+// Render renders the chart with the given renderer to the given io.Writer.
+func (bc BarChart) Render(rp RendererProvider, w io.Writer) error {
+	if len(bc.Bars) == 0 {
+		return errors.New("please provide at least one bar")
+	}
+
+	r, err := rp(bc.GetWidth(), bc.GetHeight())
+	if err != nil {
+		return err
+	}
+
+	if bc.Font == nil {
+		defaultFont, err := GetDefaultFont()
+		if err != nil {
+			return err
+		}
+		bc.defaultFont = defaultFont
+	}
+	r.SetDPI(bc.GetDPI())
+
+	bc.drawBackground(r)
+
+	var canvasBox Box
+	var yt []Tick
+	var yr Range
+	var yf ValueFormatter
+
+	canvasBox = bc.getDefaultCanvasBox()
+	yr = bc.getRanges()
+	if yr.GetMax()-yr.GetMin() == 0 {
+		return fmt.Errorf("invalid data range; cannot be zero")
+	}
+	yr = bc.setRangeDomains(canvasBox, yr)
+	yf = bc.getValueFormatters()
+
+	if bc.hasAxes() {
+		yt = bc.getAxesTicks(r, yr, yf)
+		canvasBox = bc.getAdjustedCanvasBox(r, canvasBox, yr, yt)
+		yr = bc.setRangeDomains(canvasBox, yr)
+	}
+	bc.drawCanvas(r, canvasBox)
+	bc.drawBars(r, canvasBox, yr)
+	bc.drawXAxis(r, canvasBox)
+	bc.drawYAxis(r, canvasBox, yr, yt)
+
+	bc.drawTitle(r)
+	for _, a := range bc.Elements {
+		a(r, canvasBox, bc.styleDefaultsElements())
+	}
+
+	return r.Save(w)
+}
+
+func (bc BarChart) drawCanvas(r Renderer, canvasBox Box) {
+	Draw.Box(r, canvasBox, bc.getCanvasStyle())
+}
+
+func (bc BarChart) getRanges() Range {
+	var yrange Range
+	if bc.YAxis.Range != nil && !bc.YAxis.Range.IsZero() {
+		yrange = bc.YAxis.Range
+	} else {
+		yrange = &ContinuousRange{}
+	}
+
+	if !yrange.IsZero() {
+		return yrange
+	}
+
+	if len(bc.YAxis.Ticks) > 0 {
+		tickMin, tickMax := math.MaxFloat64, -math.MaxFloat64
+		for _, t := range bc.YAxis.Ticks {
+			tickMin = math.Min(tickMin, t.Value)
+			tickMax = math.Max(tickMax, t.Value)
+		}
+		yrange.SetMin(tickMin)
+		yrange.SetMax(tickMax)
+		return yrange
+	}
+
+	min, max := math.MaxFloat64, -math.MaxFloat64
+	for _, b := range bc.Bars {
+		min = math.Min(b.Value, min)
+		max = math.Max(b.Value, max)
+	}
+
+	yrange.SetMin(min)
+	yrange.SetMax(max)
+
+	return yrange
+}
+
+func (bc BarChart) drawBackground(r Renderer) {
+	Draw.Box(r, Box{
+		Right:  bc.GetWidth(),
+		Bottom: bc.GetHeight(),
+	}, bc.getBackgroundStyle())
+}
+
+func (bc BarChart) drawBars(r Renderer, canvasBox Box, yr Range) {
+	xoffset := canvasBox.Left
+
+	width, spacing, _ := bc.calculateScaledTotalWidth(canvasBox)
+	bs2 := spacing >> 1
+
+	var barBox Box
+	var bxl, bxr, by int
+	for index, bar := range bc.Bars {
+		bxl = xoffset + bs2
+		bxr = bxl + width
+
+		by = canvasBox.Bottom - yr.Translate(bar.Value)
+
+		if bc.UseBaseValue {
+			barBox = Box{
+				Top:    by,
+				Left:   bxl,
+				Right:  bxr,
+				Bottom: canvasBox.Bottom - yr.Translate(bc.BaseValue),
+			}
+		} else {
+			barBox = Box{
+				Top:    by,
+				Left:   bxl,
+				Right:  bxr,
+				Bottom: canvasBox.Bottom,
+			}
+		}
+
+		Draw.Box(r, barBox, bar.Style.InheritFrom(bc.styleDefaultsBar(index)))
+
+		xoffset += width + spacing
+	}
+}
+
+func (bc BarChart) drawXAxis(r Renderer, canvasBox Box) {
+	if !bc.XAxis.Hidden {
+		axisStyle := bc.XAxis.InheritFrom(bc.styleDefaultsAxes())
+		axisStyle.WriteToRenderer(r)
+
+		width, spacing, _ := bc.calculateScaledTotalWidth(canvasBox)
+
+		r.MoveTo(canvasBox.Left, canvasBox.Bottom)
+		r.LineTo(canvasBox.Right, canvasBox.Bottom)
+		r.Stroke()
+
+		r.MoveTo(canvasBox.Left, canvasBox.Bottom)
+		r.LineTo(canvasBox.Left, canvasBox.Bottom+DefaultVerticalTickHeight)
+		r.Stroke()
+
+		cursor := canvasBox.Left
+		for index, bar := range bc.Bars {
+			barLabelBox := Box{
+				Top:    canvasBox.Bottom + DefaultXAxisMargin,
+				Left:   cursor,
+				Right:  cursor + width + spacing,
+				Bottom: bc.GetHeight(),
+			}
+
+			if len(bar.Label) > 0 {
+				Draw.TextWithin(r, bar.Label, barLabelBox, axisStyle)
+			}
+
+			axisStyle.WriteToRenderer(r)
+			if index < len(bc.Bars)-1 {
+				r.MoveTo(barLabelBox.Right, canvasBox.Bottom)
+				r.LineTo(barLabelBox.Right, canvasBox.Bottom+DefaultVerticalTickHeight)
+				r.Stroke()
+			}
+			cursor += width + spacing
+		}
+	}
+}
+
+func (bc BarChart) drawYAxis(r Renderer, canvasBox Box, yr Range, ticks []Tick) {
+	if !bc.YAxis.Style.Hidden {
+		bc.YAxis.Render(r, canvasBox, yr, bc.styleDefaultsAxes(), ticks)
+	}
+}
+
+func (bc BarChart) drawTitle(r Renderer) {
+	if len(bc.Title) > 0 && !bc.TitleStyle.Hidden {
+		r.SetFont(bc.TitleStyle.GetFont(bc.GetFont()))
+		r.SetFontColor(bc.TitleStyle.GetFontColor(bc.GetColorPalette().TextColor()))
+		titleFontSize := bc.TitleStyle.GetFontSize(bc.getTitleFontSize())
+		r.SetFontSize(titleFontSize)
+
+		textBox := r.MeasureText(bc.Title)
+
+		textWidth := textBox.Width()
+		textHeight := textBox.Height()
+
+		titleX := (bc.GetWidth() >> 1) - (textWidth >> 1)
+		titleY := bc.TitleStyle.Padding.GetTop(DefaultTitleTop) + textHeight
+
+		r.Text(bc.Title, titleX, titleY)
+	}
+}
+
+func (bc BarChart) getCanvasStyle() Style {
+	return bc.Canvas.InheritFrom(bc.styleDefaultsCanvas())
+}
+
+func (bc BarChart) styleDefaultsCanvas() Style {
+	return Style{
+		FillColor:   bc.GetColorPalette().CanvasColor(),
+		StrokeColor: bc.GetColorPalette().CanvasStrokeColor(),
+		StrokeWidth: DefaultCanvasStrokeWidth,
+	}
+}
+
+func (bc BarChart) hasAxes() bool {
+	return !bc.YAxis.Style.Hidden
+}
+
+func (bc BarChart) setRangeDomains(canvasBox Box, yr Range) Range {
+	yr.SetDomain(canvasBox.Height())
+	return yr
+}
+
+func (bc BarChart) getDefaultCanvasBox() Box {
+	return bc.box()
+}
+
+func (bc BarChart) getValueFormatters() ValueFormatter {
+	if bc.YAxis.ValueFormatter != nil {
+		return bc.YAxis.ValueFormatter
+	}
+	return FloatValueFormatter
+}
+
+func (bc BarChart) getAxesTicks(r Renderer, yr Range, yf ValueFormatter) (yticks []Tick) {
+	if !bc.YAxis.Style.Hidden {
+		yticks = bc.YAxis.GetTicks(r, yr, bc.styleDefaultsAxes(), yf)
+	}
+	return
+}
+
+func (bc BarChart) calculateEffectiveBarSpacing(canvasBox Box) int {
+	totalWithBaseSpacing := bc.calculateTotalBarWidth(bc.GetBarWidth(), bc.GetBarSpacing())
+	if totalWithBaseSpacing > canvasBox.Width() {
+		lessBarWidths := canvasBox.Width() - (len(bc.Bars) * bc.GetBarWidth())
+		if lessBarWidths > 0 {
+			return int(math.Ceil(float64(lessBarWidths) / float64(len(bc.Bars))))
+		}
+		return 0
+	}
+	return bc.GetBarSpacing()
+}
+
+func (bc BarChart) calculateEffectiveBarWidth(canvasBox Box, spacing int) int {
+	totalWithBaseWidth := bc.calculateTotalBarWidth(bc.GetBarWidth(), spacing)
+	if totalWithBaseWidth > canvasBox.Width() {
+		totalLessBarSpacings := canvasBox.Width() - (len(bc.Bars) * spacing)
+		if totalLessBarSpacings > 0 {
+			return int(math.Ceil(float64(totalLessBarSpacings) / float64(len(bc.Bars))))
+		}
+		return 0
+	}
+	return bc.GetBarWidth()
+}
+
+func (bc BarChart) calculateTotalBarWidth(barWidth, spacing int) int {
+	return len(bc.Bars) * (barWidth + spacing)
+}
+
+func (bc BarChart) calculateScaledTotalWidth(canvasBox Box) (width, spacing, total int) {
+	spacing = bc.calculateEffectiveBarSpacing(canvasBox)
+	width = bc.calculateEffectiveBarWidth(canvasBox, spacing)
+	total = bc.calculateTotalBarWidth(width, spacing)
+	return
+}
+
+func (bc BarChart) getAdjustedCanvasBox(r Renderer, canvasBox Box, yrange Range, yticks []Tick) Box {
+	axesOuterBox := canvasBox.Clone()
+
+	_, _, totalWidth := bc.calculateScaledTotalWidth(canvasBox)
+
+	if !bc.XAxis.Hidden {
+		xaxisHeight := DefaultVerticalTickHeight
+
+		axisStyle := bc.XAxis.InheritFrom(bc.styleDefaultsAxes())
+		axisStyle.WriteToRenderer(r)
+
+		cursor := canvasBox.Left
+		for _, bar := range bc.Bars {
+			if len(bar.Label) > 0 {
+				barLabelBox := Box{
+					Top:    canvasBox.Bottom + DefaultXAxisMargin,
+					Left:   cursor,
+					Right:  cursor + bc.GetBarWidth() + bc.GetBarSpacing(),
+					Bottom: bc.GetHeight(),
+				}
+				lines := Text.WrapFit(r, bar.Label, barLabelBox.Width(), axisStyle)
+				linesBox := Text.MeasureLines(r, lines, axisStyle)
+
+				xaxisHeight = MinInt(linesBox.Height()+(2*DefaultXAxisMargin), xaxisHeight)
+			}
+		}
+
+		xbox := Box{
+			Top:    canvasBox.Top,
+			Left:   canvasBox.Left,
+			Right:  canvasBox.Left + totalWidth,
+			Bottom: bc.GetHeight() - xaxisHeight,
+		}
+
+		axesOuterBox = axesOuterBox.Grow(xbox)
+	}
+
+	if !bc.YAxis.Style.Hidden {
+		axesBounds := bc.YAxis.Measure(r, canvasBox, yrange, bc.styleDefaultsAxes(), yticks)
+		axesOuterBox = axesOuterBox.Grow(axesBounds)
+	}
+
+	return canvasBox.OuterConstrain(bc.box(), axesOuterBox)
+}
+
+// box returns the chart bounds as a box.
+func (bc BarChart) box() Box {
+	dpr := bc.Background.Padding.GetRight(10)
+	dpb := bc.Background.Padding.GetBottom(50)
+
+	return Box{
+		Top:    bc.Background.Padding.GetTop(20),
+		Left:   bc.Background.Padding.GetLeft(20),
+		Right:  bc.GetWidth() - dpr,
+		Bottom: bc.GetHeight() - dpb,
+	}
+}
+
+func (bc BarChart) getBackgroundStyle() Style {
+	return bc.Background.InheritFrom(bc.styleDefaultsBackground())
+}
+
+func (bc BarChart) styleDefaultsBackground() Style {
+	return Style{
+		FillColor:   bc.GetColorPalette().BackgroundColor(),
+		StrokeColor: bc.GetColorPalette().BackgroundStrokeColor(),
+		StrokeWidth: DefaultStrokeWidth,
+	}
+}
+
+func (bc BarChart) styleDefaultsBar(index int) Style {
+	return Style{
+		StrokeColor: bc.GetColorPalette().GetSeriesColor(index),
+		StrokeWidth: 3.0,
+		FillColor:   bc.GetColorPalette().GetSeriesColor(index),
+	}
+}
+
+func (bc BarChart) styleDefaultsTitle() Style {
+	return bc.TitleStyle.InheritFrom(Style{
+		FontColor:           bc.GetColorPalette().TextColor(),
+		Font:                bc.GetFont(),
+		FontSize:            bc.getTitleFontSize(),
+		TextHorizontalAlign: TextHorizontalAlignCenter,
+		TextVerticalAlign:   TextVerticalAlignTop,
+		TextWrap:            TextWrapWord,
+	})
+}
+
+func (bc BarChart) getTitleFontSize() float64 {
+	effectiveDimension := MinInt(bc.GetWidth(), bc.GetHeight())
+	if effectiveDimension >= 2048 {
+		return 48
+	} else if effectiveDimension >= 1024 {
+		return 24
+	} else if effectiveDimension >= 512 {
+		return 18
+	} else if effectiveDimension >= 256 {
+		return 12
+	}
+	return 10
+}
+
+func (bc BarChart) styleDefaultsAxes() Style {
+	return Style{
+		StrokeColor:         bc.GetColorPalette().AxisStrokeColor(),
+		Font:                bc.GetFont(),
+		FontSize:            DefaultAxisFontSize,
+		FontColor:           bc.GetColorPalette().TextColor(),
+		TextHorizontalAlign: TextHorizontalAlignCenter,
+		TextVerticalAlign:   TextVerticalAlignTop,
+		TextWrap:            TextWrapWord,
+	}
+}
+
+func (bc BarChart) styleDefaultsElements() Style {
+	return Style{
+		Font: bc.GetFont(),
+	}
+}
+
+// GetColorPalette returns the color palette for the chart.
+func (bc BarChart) GetColorPalette() ColorPalette {
+	if bc.ColorPalette != nil {
+		return bc.ColorPalette
+	}
+	return AlternateColorPalette
+}

bar_chart_test.go

@@ -0,0 +1,310 @@
+package chart
+
+import (
+	"bytes"
+	"math"
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestBarChartRender(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		Width: 1024,
+		Title: "Test Title",
+		Bars: []Value{
+			{Value: 1.0, Label: "One"},
+			{Value: 2.0, Label: "Two"},
+			{Value: 3.0, Label: "Three"},
+			{Value: 4.0, Label: "Four"},
+			{Value: 5.0, Label: "Five"},
+		},
+	}
+
+	buf := bytes.NewBuffer([]byte{})
+	err := bc.Render(PNG, buf)
+	testutil.AssertNil(t, err)
+	testutil.AssertNotZero(t, buf.Len())
+}
+
+func TestBarChartRenderZero(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		Width: 1024,
+		Title: "Test Title",
+		Bars: []Value{
+			{Value: 0.0, Label: "One"},
+			{Value: 0.0, Label: "Two"},
+		},
+	}
+
+	buf := bytes.NewBuffer([]byte{})
+	err := bc.Render(PNG, buf)
+	testutil.AssertNotNil(t, err)
+}
+
+func TestBarChartProps(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{}
+
+	testutil.AssertEqual(t, DefaultDPI, bc.GetDPI())
+	bc.DPI = 100
+	testutil.AssertEqual(t, 100, bc.GetDPI())
+
+	testutil.AssertNil(t, bc.GetFont())
+	f, err := GetDefaultFont()
+	testutil.AssertNil(t, err)
+	bc.Font = f
+	testutil.AssertNotNil(t, bc.GetFont())
+
+	testutil.AssertEqual(t, DefaultChartWidth, bc.GetWidth())
+	bc.Width = DefaultChartWidth - 1
+	testutil.AssertEqual(t, DefaultChartWidth-1, bc.GetWidth())
+
+	testutil.AssertEqual(t, DefaultChartHeight, bc.GetHeight())
+	bc.Height = DefaultChartHeight - 1
+	testutil.AssertEqual(t, DefaultChartHeight-1, bc.GetHeight())
+
+	testutil.AssertEqual(t, DefaultBarSpacing, bc.GetBarSpacing())
+	bc.BarSpacing = 150
+	testutil.AssertEqual(t, 150, bc.GetBarSpacing())
+
+	testutil.AssertEqual(t, DefaultBarWidth, bc.GetBarWidth())
+	bc.BarWidth = 75
+	testutil.AssertEqual(t, 75, bc.GetBarWidth())
+}
+
+func TestBarChartRenderNoBars(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{}
+	err := bc.Render(PNG, bytes.NewBuffer([]byte{}))
+	testutil.AssertNotNil(t, err)
+}
+
+func TestBarChartGetRanges(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{}
+
+	yr := bc.getRanges()
+	testutil.AssertNotNil(t, yr)
+	testutil.AssertFalse(t, yr.IsZero())
+
+	testutil.AssertEqual(t, -math.MaxFloat64, yr.GetMax())
+	testutil.AssertEqual(t, math.MaxFloat64, yr.GetMin())
+}
+
+func TestBarChartGetRangesBarsMinMax(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		Bars: []Value{
+			{Value: 1.0},
+			{Value: 10.0},
+		},
+	}
+
+	yr := bc.getRanges()
+	testutil.AssertNotNil(t, yr)
+	testutil.AssertFalse(t, yr.IsZero())
+
+	testutil.AssertEqual(t, 10, yr.GetMax())
+	testutil.AssertEqual(t, 1, yr.GetMin())
+}
+
+func TestBarChartGetRangesMinMax(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		YAxis: YAxis{
+			Range: &ContinuousRange{
+				Min: 5.0,
+				Max: 15.0,
+			},
+			Ticks: []Tick{
+				{Value: 7.0, Label: "Foo"},
+				{Value: 11.0, Label: "Foo2"},
+			},
+		},
+		Bars: []Value{
+			{Value: 1.0},
+			{Value: 10.0},
+		},
+	}
+
+	yr := bc.getRanges()
+	testutil.AssertNotNil(t, yr)
+	testutil.AssertFalse(t, yr.IsZero())
+
+	testutil.AssertEqual(t, 15, yr.GetMax())
+	testutil.AssertEqual(t, 5, yr.GetMin())
+}
+
+func TestBarChartGetRangesTicksMinMax(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		YAxis: YAxis{
+			Ticks: []Tick{
+				{Value: 7.0, Label: "Foo"},
+				{Value: 11.0, Label: "Foo2"},
+			},
+		},
+		Bars: []Value{
+			{Value: 1.0},
+			{Value: 10.0},
+		},
+	}
+
+	yr := bc.getRanges()
+	testutil.AssertNotNil(t, yr)
+	testutil.AssertFalse(t, yr.IsZero())
+
+	testutil.AssertEqual(t, 11, yr.GetMax())
+	testutil.AssertEqual(t, 7, yr.GetMin())
+}
+
+func TestBarChartHasAxes(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{}
+	testutil.AssertTrue(t, bc.hasAxes())
+	bc.YAxis = YAxis{
+		Style: Hidden(),
+	}
+	testutil.AssertFalse(t, bc.hasAxes())
+}
+
+func TestBarChartGetDefaultCanvasBox(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{}
+	b := bc.getDefaultCanvasBox()
+	testutil.AssertFalse(t, b.IsZero())
+}
+
+func TestBarChartSetRangeDomains(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{}
+	cb := bc.box()
+	yr := bc.getRanges()
+	yr2 := bc.setRangeDomains(cb, yr)
+	testutil.AssertNotZero(t, yr2.GetDomain())
+}
+
+func TestBarChartGetValueFormatters(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{}
+	vf := bc.getValueFormatters()
+	testutil.AssertNotNil(t, vf)
+	testutil.AssertEqual(t, "1234.00", vf(1234.0))
+
+	bc.YAxis.ValueFormatter = func(_ interface{}) string { return "test" }
+	testutil.AssertEqual(t, "test", bc.getValueFormatters()(1234))
+}
+
+func TestBarChartGetAxesTicks(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		Bars: []Value{
+			{Value: 1.0},
+			{Value: 2.0},
+			{Value: 3.0},
+		},
+	}
+
+	r, err := PNG(128, 128)
+	testutil.AssertNil(t, err)
+	yr := bc.getRanges()
+	yf := bc.getValueFormatters()
+
+	bc.YAxis.Style.Hidden = true
+	ticks := bc.getAxesTicks(r, yr, yf)
+	testutil.AssertEmpty(t, ticks)
+
+	bc.YAxis.Style.Hidden = false
+	ticks = bc.getAxesTicks(r, yr, yf)
+	testutil.AssertLen(t, ticks, 2)
+}
+
+func TestBarChartCalculateEffectiveBarSpacing(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		Width:    1024,
+		BarWidth: 10,
+		Bars: []Value{
+			{Value: 1.0, Label: "One"},
+			{Value: 2.0, Label: "Two"},
+			{Value: 3.0, Label: "Three"},
+			{Value: 4.0, Label: "Four"},
+			{Value: 5.0, Label: "Five"},
+		},
+	}
+
+	spacing := bc.calculateEffectiveBarSpacing(bc.box())
+	testutil.AssertNotZero(t, spacing)
+
+	bc.BarWidth = 250
+	spacing = bc.calculateEffectiveBarSpacing(bc.box())
+	testutil.AssertZero(t, spacing)
+}
+
+func TestBarChartCalculateEffectiveBarWidth(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BarChart{
+		Width:    1024,
+		BarWidth: 10,
+		Bars: []Value{
+			{Value: 1.0, Label: "One"},
+			{Value: 2.0, Label: "Two"},
+			{Value: 3.0, Label: "Three"},
+			{Value: 4.0, Label: "Four"},
+			{Value: 5.0, Label: "Five"},
+		},
+	}
+
+	cb := bc.box()
+
+	spacing := bc.calculateEffectiveBarSpacing(bc.box())
+	testutil.AssertNotZero(t, spacing)
+
+	barWidth := bc.calculateEffectiveBarWidth(bc.box(), spacing)
+	testutil.AssertEqual(t, 10, barWidth)
+
+	bc.BarWidth = 250
+	spacing = bc.calculateEffectiveBarSpacing(bc.box())
+	testutil.AssertZero(t, spacing)
+	barWidth = bc.calculateEffectiveBarWidth(bc.box(), spacing)
+	testutil.AssertEqual(t, 199, barWidth)
+
+	testutil.AssertEqual(t, cb.Width()+1, bc.calculateTotalBarWidth(barWidth, spacing))
+
+	bw, bs, total := bc.calculateScaledTotalWidth(cb)
+	testutil.AssertEqual(t, spacing, bs)
+	testutil.AssertEqual(t, barWidth, bw)
+	testutil.AssertEqual(t, cb.Width()+1, total)
+}
+
+func TestBarChatGetTitleFontSize(t *testing.T) {
+	// replaced new assertions helper
+	size := BarChart{Width: 2049, Height: 2049}.getTitleFontSize()
+	testutil.AssertEqual(t, 48, size)
+	size = BarChart{Width: 1025, Height: 1025}.getTitleFontSize()
+	testutil.AssertEqual(t, 24, size)
+	size = BarChart{Width: 513, Height: 513}.getTitleFontSize()
+	testutil.AssertEqual(t, 18, size)
+	size = BarChart{Width: 257, Height: 257}.getTitleFontSize()
+	testutil.AssertEqual(t, 12, size)
+	size = BarChart{Width: 128, Height: 128}.getTitleFontSize()
+	testutil.AssertEqual(t, 10, size)
+}

bollinger_band_series.go

@@ -0,0 +1,135 @@
+package chart
+
+import (
+	"fmt"
+)
+
+// Interface Assertions.
+var (
+	_ Series = (*BollingerBandsSeries)(nil)
+)
+
+// BollingerBandsSeries draws bollinger bands for an inner series.
+// Bollinger bands are defined by two lines, one at SMA+k*stddev, one at SMA-k*stdev.
+type BollingerBandsSeries struct {
+	Name  string
+	Style Style
+	YAxis YAxisType
+
+	Period      int
+	K           float64
+	InnerSeries ValuesProvider
+
+	valueBuffer *ValueBuffer
+}
+
+// GetName returns the name of the time series.
+func (bbs BollingerBandsSeries) GetName() string {
+	return bbs.Name
+}
+
+// GetStyle returns the line style.
+func (bbs BollingerBandsSeries) GetStyle() Style {
+	return bbs.Style
+}
+
+// GetYAxis returns which YAxis the series draws on.
+func (bbs BollingerBandsSeries) GetYAxis() YAxisType {
+	return bbs.YAxis
+}
+
+// GetPeriod returns the window size.
+func (bbs BollingerBandsSeries) GetPeriod() int {
+	if bbs.Period == 0 {
+		return DefaultSimpleMovingAveragePeriod
+	}
+	return bbs.Period
+}
+
+// GetK returns the K value, or the number of standard deviations above and below
+// to band the simple moving average with.
+// Typical K value is 2.0.
+func (bbs BollingerBandsSeries) GetK(defaults ...float64) float64 {
+	if bbs.K == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return 2.0
+	}
+	return bbs.K
+}
+
+// Len returns the number of elements in the series.
+func (bbs BollingerBandsSeries) Len() int {
+	return bbs.InnerSeries.Len()
+}
+
+// GetBoundedValues gets the bounded value for the series.
+func (bbs *BollingerBandsSeries) GetBoundedValues(index int) (x, y1, y2 float64) {
+	if bbs.InnerSeries == nil {
+		return
+	}
+	if bbs.valueBuffer == nil || index == 0 {
+		bbs.valueBuffer = NewValueBufferWithCapacity(bbs.GetPeriod())
+	}
+	if bbs.valueBuffer.Len() >= bbs.GetPeriod() {
+		bbs.valueBuffer.Dequeue()
+	}
+	px, py := bbs.InnerSeries.GetValues(index)
+	bbs.valueBuffer.Enqueue(py)
+	x = px
+
+	ay := Seq{bbs.valueBuffer}.Average()
+	std := Seq{bbs.valueBuffer}.StdDev()
+
+	y1 = ay + (bbs.GetK() * std)
+	y2 = ay - (bbs.GetK() * std)
+	return
+}
+
+// GetBoundedLastValues returns the last bounded value for the series.
+func (bbs *BollingerBandsSeries) GetBoundedLastValues() (x, y1, y2 float64) {
+	if bbs.InnerSeries == nil {
+		return
+	}
+	period := bbs.GetPeriod()
+	seriesLength := bbs.InnerSeries.Len()
+	startAt := seriesLength - period
+	if startAt < 0 {
+		startAt = 0
+	}
+
+	vb := NewValueBufferWithCapacity(period)
+	for index := startAt; index < seriesLength; index++ {
+		xn, yn := bbs.InnerSeries.GetValues(index)
+		vb.Enqueue(yn)
+		x = xn
+	}
+
+	ay := Seq{vb}.Average()
+	std := Seq{vb}.StdDev()
+
+	y1 = ay + (bbs.GetK() * std)
+	y2 = ay - (bbs.GetK() * std)
+
+	return
+}
+
+// Render renders the series.
+func (bbs *BollingerBandsSeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) {
+	s := bbs.Style.InheritFrom(defaults.InheritFrom(Style{
+		StrokeWidth: 1.0,
+		StrokeColor: DefaultAxisColor.WithAlpha(64),
+		FillColor:   DefaultAxisColor.WithAlpha(32),
+	}))
+
+	Draw.BoundedSeries(r, canvasBox, xrange, yrange, s, bbs, bbs.GetPeriod())
+}
+
+// Validate validates the series.
+func (bbs BollingerBandsSeries) Validate() error {
+	if bbs.InnerSeries == nil {
+		return fmt.Errorf("bollinger bands series requires InnerSeries to be set")
+	}
+	return nil
+}

bollinger_band_series_test.go

@@ -0,0 +1,52 @@
+package chart
+
+import (
+	"fmt"
+	"math"
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestBollingerBandSeries(t *testing.T) {
+	// replaced new assertions helper
+
+	s1 := mockValuesProvider{
+		X: LinearRange(1.0, 100.0),
+		Y: RandomValuesWithMax(100, 1024),
+	}
+
+	bbs := &BollingerBandsSeries{
+		InnerSeries: s1,
+	}
+
+	xvalues := make([]float64, 100)
+	y1values := make([]float64, 100)
+	y2values := make([]float64, 100)
+
+	for x := 0; x < 100; x++ {
+		xvalues[x], y1values[x], y2values[x] = bbs.GetBoundedValues(x)
+	}
+
+	for x := bbs.GetPeriod(); x < 100; x++ {
+		testutil.AssertTrue(t, y1values[x] > y2values[x], fmt.Sprintf("%v vs. %v", y1values[x], y2values[x]))
+	}
+}
+
+func TestBollingerBandLastValue(t *testing.T) {
+	// replaced new assertions helper
+
+	s1 := mockValuesProvider{
+		X: LinearRange(1.0, 100.0),
+		Y: LinearRange(1.0, 100.0),
+	}
+
+	bbs := &BollingerBandsSeries{
+		InnerSeries: s1,
+	}
+
+	x, y1, y2 := bbs.GetBoundedLastValues()
+	testutil.AssertEqual(t, 100.0, x)
+	testutil.AssertEqual(t, 101, math.Floor(y1))
+	testutil.AssertEqual(t, 83, math.Floor(y2))
+}

bounded_last_values_annotation_series.go

@@ -0,0 +1,36 @@
+package chart
+
+import "fmt"
+
+// BoundedLastValuesAnnotationSeries returns a last value annotation series for a bounded values provider.
+func BoundedLastValuesAnnotationSeries(innerSeries FullBoundedValuesProvider, vfs ...ValueFormatter) AnnotationSeries {
+	lvx, lvy1, lvy2 := innerSeries.GetBoundedLastValues()
+
+	var vf ValueFormatter
+	if len(vfs) > 0 {
+		vf = vfs[0]
+	} else if typed, isTyped := innerSeries.(ValueFormatterProvider); isTyped {
+		_, vf = typed.GetValueFormatters()
+	} else {
+		vf = FloatValueFormatter
+	}
+
+	label1 := vf(lvy1)
+	label2 := vf(lvy2)
+
+	var seriesName string
+	var seriesStyle Style
+	if typed, isTyped := innerSeries.(Series); isTyped {
+		seriesName = fmt.Sprintf("%s - Last Values", typed.GetName())
+		seriesStyle = typed.GetStyle()
+	}
+
+	return AnnotationSeries{
+		Name:  seriesName,
+		Style: seriesStyle,
+		Annotations: []Value2{
+			{XValue: lvx, YValue: lvy1, Label: label1},
+			{XValue: lvx, YValue: lvy2, Label: label2},
+		},
+	}
+}

box.go

@@ -0,0 +1,367 @@
+package chart
+
+import (
+	"fmt"
+	"math"
+)
+
+var (
+	// BoxZero is a preset box that represents an intentional zero value.
+	BoxZero = Box{IsSet: true}
+)
+
+// NewBox returns a new (set) box.
+func NewBox(top, left, right, bottom int) Box {
+	return Box{
+		IsSet:  true,
+		Top:    top,
+		Left:   left,
+		Right:  right,
+		Bottom: bottom,
+	}
+}
+
+// Box represents the main 4 dimensions of a box.
+type Box struct {
+	Top    int
+	Left   int
+	Right  int
+	Bottom int
+	IsSet  bool
+}
+
+// IsZero returns if the box is set or not.
+func (b Box) IsZero() bool {
+	if b.IsSet {
+		return false
+	}
+	return b.Top == 0 && b.Left == 0 && b.Right == 0 && b.Bottom == 0
+}
+
+// String returns a string representation of the box.
+func (b Box) String() string {
+	return fmt.Sprintf("box(%d,%d,%d,%d)", b.Top, b.Left, b.Right, b.Bottom)
+}
+
+// GetTop returns a coalesced value with a default.
+func (b Box) GetTop(defaults ...int) int {
+	if !b.IsSet && b.Top == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return 0
+	}
+	return b.Top
+}
+
+// GetLeft returns a coalesced value with a default.
+func (b Box) GetLeft(defaults ...int) int {
+	if !b.IsSet && b.Left == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return 0
+	}
+	return b.Left
+}
+
+// GetRight returns a coalesced value with a default.
+func (b Box) GetRight(defaults ...int) int {
+	if !b.IsSet && b.Right == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return 0
+	}
+	return b.Right
+}
+
+// GetBottom returns a coalesced value with a default.
+func (b Box) GetBottom(defaults ...int) int {
+	if !b.IsSet && b.Bottom == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return 0
+	}
+	return b.Bottom
+}
+
+// Width returns the width
+func (b Box) Width() int {
+	return AbsInt(b.Right - b.Left)
+}
+
+// Height returns the height
+func (b Box) Height() int {
+	return AbsInt(b.Bottom - b.Top)
+}
+
+// Center returns the center of the box
+func (b Box) Center() (x, y int) {
+	w2, h2 := b.Width()>>1, b.Height()>>1
+	return b.Left + w2, b.Top + h2
+}
+
+// Aspect returns the aspect ratio of the box.
+func (b Box) Aspect() float64 {
+	return float64(b.Width()) / float64(b.Height())
+}
+
+// Clone returns a new copy of the box.
+func (b Box) Clone() Box {
+	return Box{
+		IsSet:  b.IsSet,
+		Top:    b.Top,
+		Left:   b.Left,
+		Right:  b.Right,
+		Bottom: b.Bottom,
+	}
+}
+
+// IsBiggerThan returns if a box is bigger than another box.
+func (b Box) IsBiggerThan(other Box) bool {
+	return b.Top < other.Top ||
+		b.Bottom > other.Bottom ||
+		b.Left < other.Left ||
+		b.Right > other.Right
+}
+
+// IsSmallerThan returns if a box is smaller than another box.
+func (b Box) IsSmallerThan(other Box) bool {
+	return b.Top > other.Top &&
+		b.Bottom < other.Bottom &&
+		b.Left > other.Left &&
+		b.Right < other.Right
+}
+
+// Equals returns if the box equals another box.
+func (b Box) Equals(other Box) bool {
+	return b.Top == other.Top &&
+		b.Left == other.Left &&
+		b.Right == other.Right &&
+		b.Bottom == other.Bottom
+}
+
+// Grow grows a box based on another box.
+func (b Box) Grow(other Box) Box {
+	return Box{
+		Top:    MinInt(b.Top, other.Top),
+		Left:   MinInt(b.Left, other.Left),
+		Right:  MaxInt(b.Right, other.Right),
+		Bottom: MaxInt(b.Bottom, other.Bottom),
+	}
+}
+
+// Shift pushes a box by x,y.
+func (b Box) Shift(x, y int) Box {
+	return Box{
+		Top:    b.Top + y,
+		Left:   b.Left + x,
+		Right:  b.Right + x,
+		Bottom: b.Bottom + y,
+	}
+}
+
+// Corners returns the box as a set of corners.
+func (b Box) Corners() BoxCorners {
+	return BoxCorners{
+		TopLeft:     Point{b.Left, b.Top},
+		TopRight:    Point{b.Right, b.Top},
+		BottomRight: Point{b.Right, b.Bottom},
+		BottomLeft:  Point{b.Left, b.Bottom},
+	}
+}
+
+// Fit is functionally the inverse of grow.
+// Fit maintains the original aspect ratio of the `other` box,
+// but constrains it to the bounds of the target box.
+func (b Box) Fit(other Box) Box {
+	ba := b.Aspect()
+	oa := other.Aspect()
+
+	if oa == ba {
+		return b.Clone()
+	}
+
+	bw, bh := float64(b.Width()), float64(b.Height())
+	bw2 := int(bw) >> 1
+	bh2 := int(bh) >> 1
+	if oa > ba { // ex. 16:9 vs. 4:3
+		var noh2 int
+		if oa > 1.0 {
+			noh2 = int(bw/oa) >> 1
+		} else {
+			noh2 = int(bh*oa) >> 1
+		}
+		return Box{
+			Top:    (b.Top + bh2) - noh2,
+			Left:   b.Left,
+			Right:  b.Right,
+			Bottom: (b.Top + bh2) + noh2,
+		}
+	}
+	var now2 int
+	if oa > 1.0 {
+		now2 = int(bh/oa) >> 1
+	} else {
+		now2 = int(bw*oa) >> 1
+	}
+	return Box{
+		Top:    b.Top,
+		Left:   (b.Left + bw2) - now2,
+		Right:  (b.Left + bw2) + now2,
+		Bottom: b.Bottom,
+	}
+}
+
+// Constrain is similar to `Fit` except that it will work
+// more literally like the opposite of grow.
+func (b Box) Constrain(other Box) Box {
+	newBox := b.Clone()
+
+	newBox.Top = MaxInt(newBox.Top, other.Top)
+	newBox.Left = MaxInt(newBox.Left, other.Left)
+	newBox.Right = MinInt(newBox.Right, other.Right)
+	newBox.Bottom = MinInt(newBox.Bottom, other.Bottom)
+
+	return newBox
+}
+
+// OuterConstrain is similar to `Constraint` with the difference
+// that it applies corrections
+func (b Box) OuterConstrain(bounds, other Box) Box {
+	newBox := b.Clone()
+	if other.Top < bounds.Top {
+		delta := bounds.Top - other.Top
+		newBox.Top = b.Top + delta
+	}
+
+	if other.Left < bounds.Left {
+		delta := bounds.Left - other.Left
+		newBox.Left = b.Left + delta
+	}
+
+	if other.Right > bounds.Right {
+		delta := other.Right - bounds.Right
+		newBox.Right = b.Right - delta
+	}
+
+	if other.Bottom > bounds.Bottom {
+		delta := other.Bottom - bounds.Bottom
+		newBox.Bottom = b.Bottom - delta
+	}
+	return newBox
+}
+
+func (b Box) Validate() error {
+	if b.Left < 0 {
+		return fmt.Errorf("invalid left; must be >= 0")
+	}
+	if b.Right < 0 {
+		return fmt.Errorf("invalid right; must be > 0")
+	}
+	if b.Top < 0 {
+		return fmt.Errorf("invalid top; must be > 0")
+	}
+	if b.Bottom < 0 {
+		return fmt.Errorf("invalid bottom; must be > 0")
+	}
+	return nil
+}
+
+// BoxCorners is a box with independent corners.
+type BoxCorners struct {
+	TopLeft, TopRight, BottomRight, BottomLeft Point
+}
+
+// Box return the BoxCorners as a regular box.
+func (bc BoxCorners) Box() Box {
+	return Box{
+		Top:    MinInt(bc.TopLeft.Y, bc.TopRight.Y),
+		Left:   MinInt(bc.TopLeft.X, bc.BottomLeft.X),
+		Right:  MaxInt(bc.TopRight.X, bc.BottomRight.X),
+		Bottom: MaxInt(bc.BottomLeft.Y, bc.BottomRight.Y),
+	}
+}
+
+// Width returns the width
+func (bc BoxCorners) Width() int {
+	minLeft := MinInt(bc.TopLeft.X, bc.BottomLeft.X)
+	maxRight := MaxInt(bc.TopRight.X, bc.BottomRight.X)
+	return maxRight - minLeft
+}
+
+// Height returns the height
+func (bc BoxCorners) Height() int {
+	minTop := MinInt(bc.TopLeft.Y, bc.TopRight.Y)
+	maxBottom := MaxInt(bc.BottomLeft.Y, bc.BottomRight.Y)
+	return maxBottom - minTop
+}
+
+// Center returns the center of the box
+func (bc BoxCorners) Center() (x, y int) {
+
+	left := MeanInt(bc.TopLeft.X, bc.BottomLeft.X)
+	right := MeanInt(bc.TopRight.X, bc.BottomRight.X)
+	x = ((right - left) >> 1) + left
+
+	top := MeanInt(bc.TopLeft.Y, bc.TopRight.Y)
+	bottom := MeanInt(bc.BottomLeft.Y, bc.BottomRight.Y)
+	y = ((bottom - top) >> 1) + top
+
+	return
+}
+
+// Rotate rotates the box.
+func (bc BoxCorners) Rotate(thetaDegrees float64) BoxCorners {
+	cx, cy := bc.Center()
+
+	thetaRadians := DegreesToRadians(thetaDegrees)
+
+	tlx, tly := RotateCoordinate(cx, cy, bc.TopLeft.X, bc.TopLeft.Y, thetaRadians)
+	trx, try := RotateCoordinate(cx, cy, bc.TopRight.X, bc.TopRight.Y, thetaRadians)
+	brx, bry := RotateCoordinate(cx, cy, bc.BottomRight.X, bc.BottomRight.Y, thetaRadians)
+	blx, bly := RotateCoordinate(cx, cy, bc.BottomLeft.X, bc.BottomLeft.Y, thetaRadians)
+
+	return BoxCorners{
+		TopLeft:     Point{tlx, tly},
+		TopRight:    Point{trx, try},
+		BottomRight: Point{brx, bry},
+		BottomLeft:  Point{blx, bly},
+	}
+}
+
+// Equals returns if the box equals another box.
+func (bc BoxCorners) Equals(other BoxCorners) bool {
+	return bc.TopLeft.Equals(other.TopLeft) &&
+		bc.TopRight.Equals(other.TopRight) &&
+		bc.BottomRight.Equals(other.BottomRight) &&
+		bc.BottomLeft.Equals(other.BottomLeft)
+}
+
+func (bc BoxCorners) String() string {
+	return fmt.Sprintf("BoxC{%s,%s,%s,%s}", bc.TopLeft.String(), bc.TopRight.String(), bc.BottomRight.String(), bc.BottomLeft.String())
+}
+
+// Point is an X,Y pair
+type Point struct {
+	X, Y int
+}
+
+// DistanceTo calculates the distance to another point.
+func (p Point) DistanceTo(other Point) float64 {
+	dx := math.Pow(float64(p.X-other.X), 2)
+	dy := math.Pow(float64(p.Y-other.Y), 2)
+	return math.Pow(dx+dy, 0.5)
+}
+
+// Equals returns if a point equals another point.
+func (p Point) Equals(other Point) bool {
+	return p.X == other.X && p.Y == other.Y
+}
+
+// String returns a string representation of the point.
+func (p Point) String() string {
+	return fmt.Sprintf("P{%d,%d}", p.X, p.Y)
+}

box_test.go

@@ -0,0 +1,188 @@
+package chart
+
+import (
+	"math"
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestBoxClone(t *testing.T) {
+	// replaced new assertions helper
+	a := Box{Top: 5, Left: 5, Right: 15, Bottom: 15}
+	b := a.Clone()
+	testutil.AssertTrue(t, a.Equals(b))
+	testutil.AssertTrue(t, b.Equals(a))
+}
+
+func TestBoxEquals(t *testing.T) {
+	// replaced new assertions helper
+
+	a := Box{Top: 5, Left: 5, Right: 15, Bottom: 15}
+	b := Box{Top: 10, Left: 10, Right: 30, Bottom: 30}
+	c := Box{Top: 5, Left: 5, Right: 15, Bottom: 15}
+	testutil.AssertTrue(t, a.Equals(a))
+	testutil.AssertTrue(t, a.Equals(c))
+	testutil.AssertTrue(t, c.Equals(a))
+	testutil.AssertFalse(t, a.Equals(b))
+	testutil.AssertFalse(t, c.Equals(b))
+	testutil.AssertFalse(t, b.Equals(a))
+	testutil.AssertFalse(t, b.Equals(c))
+}
+
+func TestBoxIsBiggerThan(t *testing.T) {
+	// replaced new assertions helper
+
+	a := Box{Top: 5, Left: 5, Right: 25, Bottom: 25}
+	b := Box{Top: 10, Left: 10, Right: 20, Bottom: 20} // only half bigger
+	c := Box{Top: 1, Left: 1, Right: 30, Bottom: 30}   //bigger
+	testutil.AssertTrue(t, a.IsBiggerThan(b))
+	testutil.AssertFalse(t, a.IsBiggerThan(c))
+	testutil.AssertTrue(t, c.IsBiggerThan(a))
+}
+
+func TestBoxIsSmallerThan(t *testing.T) {
+	// replaced new assertions helper
+
+	a := Box{Top: 5, Left: 5, Right: 25, Bottom: 25}
+	b := Box{Top: 10, Left: 10, Right: 20, Bottom: 20} // only half bigger
+	c := Box{Top: 1, Left: 1, Right: 30, Bottom: 30}   //bigger
+	testutil.AssertFalse(t, a.IsSmallerThan(b))
+	testutil.AssertTrue(t, a.IsSmallerThan(c))
+	testutil.AssertFalse(t, c.IsSmallerThan(a))
+}
+
+func TestBoxGrow(t *testing.T) {
+	// replaced new assertions helper
+
+	a := Box{Top: 1, Left: 2, Right: 15, Bottom: 15}
+	b := Box{Top: 4, Left: 5, Right: 30, Bottom: 35}
+	c := a.Grow(b)
+	testutil.AssertFalse(t, c.Equals(b))
+	testutil.AssertFalse(t, c.Equals(a))
+	testutil.AssertEqual(t, 1, c.Top)
+	testutil.AssertEqual(t, 2, c.Left)
+	testutil.AssertEqual(t, 30, c.Right)
+	testutil.AssertEqual(t, 35, c.Bottom)
+}
+
+func TestBoxFit(t *testing.T) {
+	// replaced new assertions helper
+
+	a := Box{Top: 64, Left: 64, Right: 192, Bottom: 192}
+	b := Box{Top: 16, Left: 16, Right: 256, Bottom: 170}
+	c := Box{Top: 16, Left: 16, Right: 170, Bottom: 256}
+
+	fab := a.Fit(b)
+	testutil.AssertEqual(t, a.Left, fab.Left)
+	testutil.AssertEqual(t, a.Right, fab.Right)
+	testutil.AssertTrue(t, fab.Top < fab.Bottom)
+	testutil.AssertTrue(t, fab.Left < fab.Right)
+	testutil.AssertTrue(t, math.Abs(b.Aspect()-fab.Aspect()) < 0.02)
+
+	fac := a.Fit(c)
+	testutil.AssertEqual(t, a.Top, fac.Top)
+	testutil.AssertEqual(t, a.Bottom, fac.Bottom)
+	testutil.AssertTrue(t, math.Abs(c.Aspect()-fac.Aspect()) < 0.02)
+}
+
+func TestBoxConstrain(t *testing.T) {
+	// replaced new assertions helper
+
+	a := Box{Top: 64, Left: 64, Right: 192, Bottom: 192}
+	b := Box{Top: 16, Left: 16, Right: 256, Bottom: 170}
+	c := Box{Top: 16, Left: 16, Right: 170, Bottom: 256}
+
+	cab := a.Constrain(b)
+	testutil.AssertEqual(t, 64, cab.Top)
+	testutil.AssertEqual(t, 64, cab.Left)
+	testutil.AssertEqual(t, 192, cab.Right)
+	testutil.AssertEqual(t, 170, cab.Bottom)
+
+	cac := a.Constrain(c)
+	testutil.AssertEqual(t, 64, cac.Top)
+	testutil.AssertEqual(t, 64, cac.Left)
+	testutil.AssertEqual(t, 170, cac.Right)
+	testutil.AssertEqual(t, 192, cac.Bottom)
+}
+
+func TestBoxOuterConstrain(t *testing.T) {
+	// replaced new assertions helper
+
+	box := NewBox(0, 0, 100, 100)
+	canvas := NewBox(5, 5, 95, 95)
+	taller := NewBox(-10, 5, 50, 50)
+
+	c := canvas.OuterConstrain(box, taller)
+	testutil.AssertEqual(t, 15, c.Top, c.String())
+	testutil.AssertEqual(t, 5, c.Left, c.String())
+	testutil.AssertEqual(t, 95, c.Right, c.String())
+	testutil.AssertEqual(t, 95, c.Bottom, c.String())
+
+	wider := NewBox(5, 5, 110, 50)
+	d := canvas.OuterConstrain(box, wider)
+	testutil.AssertEqual(t, 5, d.Top, d.String())
+	testutil.AssertEqual(t, 5, d.Left, d.String())
+	testutil.AssertEqual(t, 85, d.Right, d.String())
+	testutil.AssertEqual(t, 95, d.Bottom, d.String())
+}
+
+func TestBoxShift(t *testing.T) {
+	// replaced new assertions helper
+
+	b := Box{
+		Top:    5,
+		Left:   5,
+		Right:  10,
+		Bottom: 10,
+	}
+
+	shifted := b.Shift(1, 2)
+	testutil.AssertEqual(t, 7, shifted.Top)
+	testutil.AssertEqual(t, 6, shifted.Left)
+	testutil.AssertEqual(t, 11, shifted.Right)
+	testutil.AssertEqual(t, 12, shifted.Bottom)
+}
+
+func TestBoxCenter(t *testing.T) {
+	// replaced new assertions helper
+
+	b := Box{
+		Top:    10,
+		Left:   10,
+		Right:  20,
+		Bottom: 30,
+	}
+	cx, cy := b.Center()
+	testutil.AssertEqual(t, 15, cx)
+	testutil.AssertEqual(t, 20, cy)
+}
+
+func TestBoxCornersCenter(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BoxCorners{
+		TopLeft:     Point{5, 5},
+		TopRight:    Point{15, 5},
+		BottomRight: Point{15, 15},
+		BottomLeft:  Point{5, 15},
+	}
+
+	cx, cy := bc.Center()
+	testutil.AssertEqual(t, 10, cx)
+	testutil.AssertEqual(t, 10, cy)
+}
+
+func TestBoxCornersRotate(t *testing.T) {
+	// replaced new assertions helper
+
+	bc := BoxCorners{
+		TopLeft:     Point{5, 5},
+		TopRight:    Point{15, 5},
+		BottomRight: Point{15, 15},
+		BottomLeft:  Point{5, 15},
+	}
+
+	rotated := bc.Rotate(45)
+	testutil.AssertTrue(t, rotated.TopLeft.Equals(Point{10, 3}), rotated.String())
+}

chart.go

@@ -0,0 +1,577 @@
+package chart
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"math"
+
+	"github.com/golang/freetype/truetype"
+)
+
+// Chart is what we're drawing.
+type Chart struct {
+	Title      string
+	TitleStyle Style
+
+	ColorPalette ColorPalette
+
+	Width  int
+	Height int
+	DPI    float64
+
+	Background Style
+	Canvas     Style
+
+	XAxis          XAxis
+	YAxis          YAxis
+	YAxisSecondary YAxis
+
+	Font        *truetype.Font
+	defaultFont *truetype.Font
+
+	Series   []Series
+	Elements []Renderable
+
+	Log Logger
+}
+
+// GetDPI returns the dpi for the chart.
+func (c Chart) GetDPI(defaults ...float64) float64 {
+	if c.DPI == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return DefaultDPI
+	}
+	return c.DPI
+}
+
+// GetFont returns the text font.
+func (c Chart) GetFont() *truetype.Font {
+	if c.Font == nil {
+		return c.defaultFont
+	}
+	return c.Font
+}
+
+// GetWidth returns the chart width or the default value.
+func (c Chart) GetWidth() int {
+	if c.Width == 0 {
+		return DefaultChartWidth
+	}
+	return c.Width
+}
+
+// GetHeight returns the chart height or the default value.
+func (c Chart) GetHeight() int {
+	if c.Height == 0 {
+		return DefaultChartHeight
+	}
+	return c.Height
+}
+
+// Render renders the chart with the given renderer to the given io.Writer.
+func (c Chart) Render(rp RendererProvider, w io.Writer) error {
+	if len(c.Series) == 0 {
+		return errors.New("please provide at least one series")
+	}
+	if err := c.checkHasVisibleSeries(); err != nil {
+		return err
+	}
+
+	c.YAxisSecondary.AxisType = YAxisSecondary
+
+	r, err := rp(c.GetWidth(), c.GetHeight())
+	if err != nil {
+		return err
+	}
+
+	if c.Font == nil {
+		defaultFont, err := GetDefaultFont()
+		if err != nil {
+			return err
+		}
+		c.defaultFont = defaultFont
+	}
+	r.SetDPI(c.GetDPI(DefaultDPI))
+
+	c.drawBackground(r)
+
+	var xt, yt, yta []Tick
+	xr, yr, yra := c.getRanges()
+	canvasBox := c.getDefaultCanvasBox()
+	xf, yf, yfa := c.getValueFormatters()
+
+	Debugf(c.Log, "chart; canvas box: %v", canvasBox)
+
+	xr, yr, yra = c.setRangeDomains(canvasBox, xr, yr, yra)
+
+	err = c.checkRanges(xr, yr, yra)
+	if err != nil {
+		r.Save(w)
+		return err
+	}
+
+	if c.hasAxes() {
+		xt, yt, yta = c.getAxesTicks(r, xr, yr, yra, xf, yf, yfa)
+		canvasBox = c.getAxesAdjustedCanvasBox(r, canvasBox, xr, yr, yra, xt, yt, yta)
+		xr, yr, yra = c.setRangeDomains(canvasBox, xr, yr, yra)
+
+		Debugf(c.Log, "chart; axes adjusted canvas box: %v", canvasBox)
+
+		// do a second pass in case things haven't settled yet.
+		xt, yt, yta = c.getAxesTicks(r, xr, yr, yra, xf, yf, yfa)
+		canvasBox = c.getAxesAdjustedCanvasBox(r, canvasBox, xr, yr, yra, xt, yt, yta)
+		xr, yr, yra = c.setRangeDomains(canvasBox, xr, yr, yra)
+	}
+
+	if c.hasAnnotationSeries() {
+		canvasBox = c.getAnnotationAdjustedCanvasBox(r, canvasBox, xr, yr, yra, xf, yf, yfa)
+		xr, yr, yra = c.setRangeDomains(canvasBox, xr, yr, yra)
+		xt, yt, yta = c.getAxesTicks(r, xr, yr, yra, xf, yf, yfa)
+
+		Debugf(c.Log, "chart; annotation adjusted canvas box: %v", canvasBox)
+	}
+
+	c.drawCanvas(r, canvasBox)
+	c.drawAxes(r, canvasBox, xr, yr, yra, xt, yt, yta)
+	for index, series := range c.Series {
+		c.drawSeries(r, canvasBox, xr, yr, yra, series, index)
+	}
+
+	c.drawTitle(r)
+
+	for _, a := range c.Elements {
+		a(r, canvasBox, c.styleDefaultsElements())
+	}
+
+	return r.Save(w)
+}
+
+func (c Chart) checkHasVisibleSeries() error {
+	var style Style
+	for _, s := range c.Series {
+		style = s.GetStyle()
+		if !style.Hidden {
+			return nil
+		}
+	}
+	return fmt.Errorf("chart render; must have (1) visible series")
+}
+
+func (c Chart) validateSeries() error {
+	var err error
+	for _, s := range c.Series {
+		err = s.Validate()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (c Chart) getRanges() (xrange, yrange, yrangeAlt Range) {
+	var minx, maxx float64 = math.MaxFloat64, -math.MaxFloat64
+	var miny, maxy float64 = math.MaxFloat64, -math.MaxFloat64
+	var minya, maxya float64 = math.MaxFloat64, -math.MaxFloat64
+
+	seriesMappedToSecondaryAxis := false
+
+	// note: a possible future optimization is to not scan the series values if
+	// all axis are represented by either custom ticks or custom ranges.
+	for _, s := range c.Series {
+		if !s.GetStyle().Hidden {
+			seriesAxis := s.GetYAxis()
+			if bvp, isBoundedValuesProvider := s.(BoundedValuesProvider); isBoundedValuesProvider {
+				seriesLength := bvp.Len()
+				for index := 0; index < seriesLength; index++ {
+					vx, vy1, vy2 := bvp.GetBoundedValues(index)
+
+					minx = math.Min(minx, vx)
+					maxx = math.Max(maxx, vx)
+
+					if seriesAxis == YAxisPrimary {
+						miny = math.Min(miny, vy1)
+						miny = math.Min(miny, vy2)
+						maxy = math.Max(maxy, vy1)
+						maxy = math.Max(maxy, vy2)
+					} else if seriesAxis == YAxisSecondary {
+						minya = math.Min(minya, vy1)
+						minya = math.Min(minya, vy2)
+						maxya = math.Max(maxya, vy1)
+						maxya = math.Max(maxya, vy2)
+						seriesMappedToSecondaryAxis = true
+					}
+				}
+			} else if vp, isValuesProvider := s.(ValuesProvider); isValuesProvider {
+				seriesLength := vp.Len()
+				for index := 0; index < seriesLength; index++ {
+					vx, vy := vp.GetValues(index)
+
+					minx = math.Min(minx, vx)
+					maxx = math.Max(maxx, vx)
+
+					if seriesAxis == YAxisPrimary {
+						miny = math.Min(miny, vy)
+						maxy = math.Max(maxy, vy)
+					} else if seriesAxis == YAxisSecondary {
+						minya = math.Min(minya, vy)
+						maxya = math.Max(maxya, vy)
+						seriesMappedToSecondaryAxis = true
+					}
+				}
+			}
+		}
+	}
+
+	if c.XAxis.Range == nil {
+		xrange = &ContinuousRange{}
+	} else {
+		xrange = c.XAxis.Range
+	}
+
+	if c.YAxis.Range == nil {
+		yrange = &ContinuousRange{}
+	} else {
+		yrange = c.YAxis.Range
+	}
+
+	if c.YAxisSecondary.Range == nil {
+		yrangeAlt = &ContinuousRange{}
+	} else {
+		yrangeAlt = c.YAxisSecondary.Range
+	}
+
+	if len(c.XAxis.Ticks) > 0 {
+		tickMin, tickMax := math.MaxFloat64, -math.MaxFloat64
+		for _, t := range c.XAxis.Ticks {
+			tickMin = math.Min(tickMin, t.Value)
+			tickMax = math.Max(tickMax, t.Value)
+		}
+		xrange.SetMin(tickMin)
+		xrange.SetMax(tickMax)
+	} else if xrange.IsZero() {
+		xrange.SetMin(minx)
+		xrange.SetMax(maxx)
+	}
+
+	if len(c.YAxis.Ticks) > 0 {
+		tickMin, tickMax := math.MaxFloat64, -math.MaxFloat64
+		for _, t := range c.YAxis.Ticks {
+			tickMin = math.Min(tickMin, t.Value)
+			tickMax = math.Max(tickMax, t.Value)
+		}
+		yrange.SetMin(tickMin)
+		yrange.SetMax(tickMax)
+	} else if yrange.IsZero() {
+		yrange.SetMin(miny)
+		yrange.SetMax(maxy)
+
+		if !c.YAxis.Style.Hidden {
+			delta := yrange.GetDelta()
+			roundTo := GetRoundToForDelta(delta)
+			rmin, rmax := RoundDown(yrange.GetMin(), roundTo), RoundUp(yrange.GetMax(), roundTo)
+
+			yrange.SetMin(rmin)
+			yrange.SetMax(rmax)
+		}
+	}
+
+	if len(c.YAxisSecondary.Ticks) > 0 {
+		tickMin, tickMax := math.MaxFloat64, -math.MaxFloat64
+		for _, t := range c.YAxis.Ticks {
+			tickMin = math.Min(tickMin, t.Value)
+			tickMax = math.Max(tickMax, t.Value)
+		}
+		yrangeAlt.SetMin(tickMin)
+		yrangeAlt.SetMax(tickMax)
+	} else if seriesMappedToSecondaryAxis && yrangeAlt.IsZero() {
+		yrangeAlt.SetMin(minya)
+		yrangeAlt.SetMax(maxya)
+
+		if !c.YAxisSecondary.Style.Hidden {
+			delta := yrangeAlt.GetDelta()
+			roundTo := GetRoundToForDelta(delta)
+			rmin, rmax := RoundDown(yrangeAlt.GetMin(), roundTo), RoundUp(yrangeAlt.GetMax(), roundTo)
+			yrangeAlt.SetMin(rmin)
+			yrangeAlt.SetMax(rmax)
+		}
+	}
+
+	return
+}
+
+func (c Chart) checkRanges(xr, yr, yra Range) error {
+	Debugf(c.Log, "checking xrange: %v", xr)
+	xDelta := xr.GetDelta()
+	if math.IsInf(xDelta, 0) {
+		return errors.New("infinite x-range delta")
+	}
+	if math.IsNaN(xDelta) {
+		return errors.New("nan x-range delta")
+	}
+	if xDelta == 0 {
+		return errors.New("zero x-range delta; there needs to be at least (2) values")
+	}
+
+	Debugf(c.Log, "checking yrange: %v", yr)
+	yDelta := yr.GetDelta()
+	if math.IsInf(yDelta, 0) {
+		return errors.New("infinite y-range delta")
+	}
+	if math.IsNaN(yDelta) {
+		return errors.New("nan y-range delta")
+	}
+
+	if c.hasSecondarySeries() {
+		Debugf(c.Log, "checking secondary yrange: %v", yra)
+		yraDelta := yra.GetDelta()
+		if math.IsInf(yraDelta, 0) {
+			return errors.New("infinite secondary y-range delta")
+		}
+		if math.IsNaN(yraDelta) {
+			return errors.New("nan secondary y-range delta")
+		}
+	}
+
+	return nil
+}
+
+func (c Chart) getDefaultCanvasBox() Box {
+	return c.Box()
+}
+
+func (c Chart) getValueFormatters() (x, y, ya ValueFormatter) {
+	for _, s := range c.Series {
+		if vfp, isVfp := s.(ValueFormatterProvider); isVfp {
+			sx, sy := vfp.GetValueFormatters()
+			if s.GetYAxis() == YAxisPrimary {
+				x = sx
+				y = sy
+			} else if s.GetYAxis() == YAxisSecondary {
+				x = sx
+				ya = sy
+			}
+		}
+	}
+	if c.XAxis.ValueFormatter != nil {
+		x = c.XAxis.GetValueFormatter()
+	}
+	if c.YAxis.ValueFormatter != nil {
+		y = c.YAxis.GetValueFormatter()
+	}
+	if c.YAxisSecondary.ValueFormatter != nil {
+		ya = c.YAxisSecondary.GetValueFormatter()
+	}
+	return
+}
+
+func (c Chart) hasAxes() bool {
+	return !c.XAxis.Style.Hidden || !c.YAxis.Style.Hidden || !c.YAxisSecondary.Style.Hidden
+}
+
+func (c Chart) getAxesTicks(r Renderer, xr, yr, yar Range, xf, yf, yfa ValueFormatter) (xticks, yticks, yticksAlt []Tick) {
+	if !c.XAxis.Style.Hidden {
+		xticks = c.XAxis.GetTicks(r, xr, c.styleDefaultsAxes(), xf)
+	}
+	if !c.YAxis.Style.Hidden {
+		yticks = c.YAxis.GetTicks(r, yr, c.styleDefaultsAxes(), yf)
+	}
+	if !c.YAxisSecondary.Style.Hidden {
+		yticksAlt = c.YAxisSecondary.GetTicks(r, yar, c.styleDefaultsAxes(), yfa)
+	}
+	return
+}
+
+func (c Chart) getAxesAdjustedCanvasBox(r Renderer, canvasBox Box, xr, yr, yra Range, xticks, yticks, yticksAlt []Tick) Box {
+	axesOuterBox := canvasBox.Clone()
+	if !c.XAxis.Style.Hidden {
+		axesBounds := c.XAxis.Measure(r, canvasBox, xr, c.styleDefaultsAxes(), xticks)
+		Debugf(c.Log, "chart; x-axis measured %v", axesBounds)
+		axesOuterBox = axesOuterBox.Grow(axesBounds)
+	}
+	if !c.YAxis.Style.Hidden {
+		axesBounds := c.YAxis.Measure(r, canvasBox, yr, c.styleDefaultsAxes(), yticks)
+		Debugf(c.Log, "chart; y-axis measured %v", axesBounds)
+		axesOuterBox = axesOuterBox.Grow(axesBounds)
+	}
+	if !c.YAxisSecondary.Style.Hidden && c.hasSecondarySeries() {
+		axesBounds := c.YAxisSecondary.Measure(r, canvasBox, yra, c.styleDefaultsAxes(), yticksAlt)
+		Debugf(c.Log, "chart; y-axis secondary measured %v", axesBounds)
+		axesOuterBox = axesOuterBox.Grow(axesBounds)
+	}
+
+	return canvasBox.OuterConstrain(c.Box(), axesOuterBox)
+}
+
+func (c Chart) setRangeDomains(canvasBox Box, xr, yr, yra Range) (Range, Range, Range) {
+	xr.SetDomain(canvasBox.Width())
+	yr.SetDomain(canvasBox.Height())
+	yra.SetDomain(canvasBox.Height())
+	return xr, yr, yra
+}
+
+func (c Chart) hasAnnotationSeries() bool {
+	for _, s := range c.Series {
+		if as, isAnnotationSeries := s.(AnnotationSeries); isAnnotationSeries {
+			if !as.GetStyle().Hidden {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (c Chart) hasSecondarySeries() bool {
+	for _, s := range c.Series {
+		if s.GetYAxis() == YAxisSecondary {
+			return true
+		}
+	}
+	return false
+}
+
+func (c Chart) getAnnotationAdjustedCanvasBox(r Renderer, canvasBox Box, xr, yr, yra Range, xf, yf, yfa ValueFormatter) Box {
+	annotationSeriesBox := canvasBox.Clone()
+	for seriesIndex, s := range c.Series {
+		if as, isAnnotationSeries := s.(AnnotationSeries); isAnnotationSeries {
+			if !as.GetStyle().Hidden {
+				style := c.styleDefaultsSeries(seriesIndex)
+				var annotationBounds Box
+				if as.YAxis == YAxisPrimary {
+					annotationBounds = as.Measure(r, canvasBox, xr, yr, style)
+				} else if as.YAxis == YAxisSecondary {
+					annotationBounds = as.Measure(r, canvasBox, xr, yra, style)
+				}
+
+				annotationSeriesBox = annotationSeriesBox.Grow(annotationBounds)
+			}
+		}
+	}
+
+	return canvasBox.OuterConstrain(c.Box(), annotationSeriesBox)
+}
+
+func (c Chart) getBackgroundStyle() Style {
+	return c.Background.InheritFrom(c.styleDefaultsBackground())
+}
+
+func (c Chart) drawBackground(r Renderer) {
+	Draw.Box(r, Box{
+		Right:  c.GetWidth(),
+		Bottom: c.GetHeight(),
+	}, c.getBackgroundStyle())
+}
+
+func (c Chart) getCanvasStyle() Style {
+	return c.Canvas.InheritFrom(c.styleDefaultsCanvas())
+}
+
+func (c Chart) drawCanvas(r Renderer, canvasBox Box) {
+	Draw.Box(r, canvasBox, c.getCanvasStyle())
+}
+
+func (c Chart) drawAxes(r Renderer, canvasBox Box, xrange, yrange, yrangeAlt Range, xticks, yticks, yticksAlt []Tick) {
+	if !c.XAxis.Style.Hidden {
+		c.XAxis.Render(r, canvasBox, xrange, c.styleDefaultsAxes(), xticks)
+	}
+	if !c.YAxis.Style.Hidden {
+		c.YAxis.Render(r, canvasBox, yrange, c.styleDefaultsAxes(), yticks)
+	}
+	if !c.YAxisSecondary.Style.Hidden {
+		c.YAxisSecondary.Render(r, canvasBox, yrangeAlt, c.styleDefaultsAxes(), yticksAlt)
+	}
+}
+
+func (c Chart) drawSeries(r Renderer, canvasBox Box, xrange, yrange, yrangeAlt Range, s Series, seriesIndex int) {
+	if !s.GetStyle().Hidden {
+		if s.GetYAxis() == YAxisPrimary {
+			s.Render(r, canvasBox, xrange, yrange, c.styleDefaultsSeries(seriesIndex))
+		} else if s.GetYAxis() == YAxisSecondary {
+			s.Render(r, canvasBox, xrange, yrangeAlt, c.styleDefaultsSeries(seriesIndex))
+		}
+	}
+}
+
+func (c Chart) drawTitle(r Renderer) {
+	if len(c.Title) > 0 && !c.TitleStyle.Hidden {
+		r.SetFont(c.TitleStyle.GetFont(c.GetFont()))
+		r.SetFontColor(c.TitleStyle.GetFontColor(c.GetColorPalette().TextColor()))
+		titleFontSize := c.TitleStyle.GetFontSize(DefaultTitleFontSize)
+		r.SetFontSize(titleFontSize)
+
+		textBox := r.MeasureText(c.Title)
+
+		textWidth := textBox.Width()
+		textHeight := textBox.Height()
+
+		titleX := (c.GetWidth() >> 1) - (textWidth >> 1)
+		titleY := c.TitleStyle.Padding.GetTop(DefaultTitleTop) + textHeight
+
+		r.Text(c.Title, titleX, titleY)
+	}
+}
+
+func (c Chart) styleDefaultsBackground() Style {
+	return Style{
+		FillColor:   c.GetColorPalette().BackgroundColor(),
+		StrokeColor: c.GetColorPalette().BackgroundStrokeColor(),
+		StrokeWidth: DefaultBackgroundStrokeWidth,
+	}
+}
+
+func (c Chart) styleDefaultsCanvas() Style {
+	return Style{
+		FillColor:   c.GetColorPalette().CanvasColor(),
+		StrokeColor: c.GetColorPalette().CanvasStrokeColor(),
+		StrokeWidth: DefaultCanvasStrokeWidth,
+	}
+}
+
+func (c Chart) styleDefaultsSeries(seriesIndex int) Style {
+	return Style{
+		DotColor:    c.GetColorPalette().GetSeriesColor(seriesIndex),
+		StrokeColor: c.GetColorPalette().GetSeriesColor(seriesIndex),
+		StrokeWidth: DefaultSeriesLineWidth,
+		Font:        c.GetFont(),
+		FontSize:    DefaultFontSize,
+	}
+}
+
+func (c Chart) styleDefaultsAxes() Style {
+	return Style{
+		Font:        c.GetFont(),
+		FontColor:   c.GetColorPalette().TextColor(),
+		FontSize:    DefaultAxisFontSize,
+		StrokeColor: c.GetColorPalette().AxisStrokeColor(),
+		StrokeWidth: DefaultAxisLineWidth,
+	}
+}
+
+func (c Chart) styleDefaultsElements() Style {
+	return Style{
+		Font: c.GetFont(),
+	}
+}
+
+// GetColorPalette returns the color palette for the chart.
+func (c Chart) GetColorPalette() ColorPalette {
+	if c.ColorPalette != nil {
+		return c.ColorPalette
+	}
+	return DefaultColorPalette
+}
+
+// Box returns the chart bounds as a box.
+func (c Chart) Box() Box {
+	dpr := c.Background.Padding.GetRight(DefaultBackgroundPadding.Right)
+	dpb := c.Background.Padding.GetBottom(DefaultBackgroundPadding.Bottom)
+
+	return Box{
+		Top:    c.Background.Padding.GetTop(DefaultBackgroundPadding.Top),
+		Left:   c.Background.Padding.GetLeft(DefaultBackgroundPadding.Left),
+		Right:  c.GetWidth() - dpr,
+		Bottom: c.GetHeight() - dpb,
+	}
+}

chart_test.go

@@ -0,0 +1,594 @@
+package chart
+
+import (
+	"bytes"
+	"image"
+	"image/png"
+	"math"
+	"testing"
+	"time"
+
+	"github.com/wcharczuk/go-chart/v2/drawing"
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestChartGetDPI(t *testing.T) {
+	// replaced new assertions helper
+
+	unset := Chart{}
+	testutil.AssertEqual(t, DefaultDPI, unset.GetDPI())
+	testutil.AssertEqual(t, 192, unset.GetDPI(192))
+
+	set := Chart{DPI: 128}
+	testutil.AssertEqual(t, 128, set.GetDPI())
+	testutil.AssertEqual(t, 128, set.GetDPI(192))
+}
+
+func TestChartGetFont(t *testing.T) {
+	// replaced new assertions helper
+
+	f, err := GetDefaultFont()
+	testutil.AssertNil(t, err)
+
+	unset := Chart{}
+	testutil.AssertNil(t, unset.GetFont())
+
+	set := Chart{Font: f}
+	testutil.AssertNotNil(t, set.GetFont())
+}
+
+func TestChartGetWidth(t *testing.T) {
+	// replaced new assertions helper
+
+	unset := Chart{}
+	testutil.AssertEqual(t, DefaultChartWidth, unset.GetWidth())
+
+	set := Chart{Width: DefaultChartWidth + 10}
+	testutil.AssertEqual(t, DefaultChartWidth+10, set.GetWidth())
+}
+
+func TestChartGetHeight(t *testing.T) {
+	// replaced new assertions helper
+
+	unset := Chart{}
+	testutil.AssertEqual(t, DefaultChartHeight, unset.GetHeight())
+
+	set := Chart{Height: DefaultChartHeight + 10}
+	testutil.AssertEqual(t, DefaultChartHeight+10, set.GetHeight())
+}
+
+func TestChartGetRanges(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{-2.0, -1.0, 0, 1.0, 2.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 4.5},
+			},
+			ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{-2.1, -1.0, 0, 1.0, 2.0},
+			},
+			ContinuousSeries{
+				YAxis:   YAxisSecondary,
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{10.0, 11.0, 12.0, 13.0, 14.0},
+			},
+		},
+	}
+
+	xrange, yrange, yrangeAlt := c.getRanges()
+	testutil.AssertEqual(t, -2.0, xrange.GetMin())
+	testutil.AssertEqual(t, 5.0, xrange.GetMax())
+
+	testutil.AssertEqual(t, -2.1, yrange.GetMin())
+	testutil.AssertEqual(t, 4.5, yrange.GetMax())
+
+	testutil.AssertEqual(t, 10.0, yrangeAlt.GetMin())
+	testutil.AssertEqual(t, 14.0, yrangeAlt.GetMax())
+
+	cSet := Chart{
+		XAxis: XAxis{
+			Range: &ContinuousRange{Min: 9.8, Max: 19.8},
+		},
+		YAxis: YAxis{
+			Range: &ContinuousRange{Min: 9.9, Max: 19.9},
+		},
+		YAxisSecondary: YAxis{
+			Range: &ContinuousRange{Min: 9.7, Max: 19.7},
+		},
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{-2.0, -1.0, 0, 1.0, 2.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 4.5},
+			},
+			ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{-2.1, -1.0, 0, 1.0, 2.0},
+			},
+			ContinuousSeries{
+				YAxis:   YAxisSecondary,
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{10.0, 11.0, 12.0, 13.0, 14.0},
+			},
+		},
+	}
+
+	xr2, yr2, yra2 := cSet.getRanges()
+	testutil.AssertEqual(t, 9.8, xr2.GetMin())
+	testutil.AssertEqual(t, 19.8, xr2.GetMax())
+
+	testutil.AssertEqual(t, 9.9, yr2.GetMin())
+	testutil.AssertEqual(t, 19.9, yr2.GetMax())
+
+	testutil.AssertEqual(t, 9.7, yra2.GetMin())
+	testutil.AssertEqual(t, 19.7, yra2.GetMax())
+}
+
+func TestChartGetRangesUseTicks(t *testing.T) {
+	// replaced new assertions helper
+
+	// this test asserts that ticks should supercede manual ranges when generating the overall ranges.
+
+	c := Chart{
+		YAxis: YAxis{
+			Ticks: []Tick{
+				{0.0, "Zero"},
+				{1.0, "1.0"},
+				{2.0, "2.0"},
+				{3.0, "3.0"},
+				{4.0, "4.0"},
+				{5.0, "Five"},
+			},
+			Range: &ContinuousRange{
+				Min: -5.0,
+				Max: 5.0,
+			},
+		},
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{-2.0, -1.0, 0, 1.0, 2.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 4.5},
+			},
+		},
+	}
+
+	xr, yr, yar := c.getRanges()
+	testutil.AssertEqual(t, -2.0, xr.GetMin())
+	testutil.AssertEqual(t, 2.0, xr.GetMax())
+	testutil.AssertEqual(t, 0.0, yr.GetMin())
+	testutil.AssertEqual(t, 5.0, yr.GetMax())
+	testutil.AssertTrue(t, yar.IsZero(), yar.String())
+}
+
+func TestChartGetRangesUseUserRanges(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		YAxis: YAxis{
+			Range: &ContinuousRange{
+				Min: -5.0,
+				Max: 5.0,
+			},
+		},
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{-2.0, -1.0, 0, 1.0, 2.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 4.5},
+			},
+		},
+	}
+
+	xr, yr, yar := c.getRanges()
+	testutil.AssertEqual(t, -2.0, xr.GetMin())
+	testutil.AssertEqual(t, 2.0, xr.GetMax())
+	testutil.AssertEqual(t, -5.0, yr.GetMin())
+	testutil.AssertEqual(t, 5.0, yr.GetMax())
+	testutil.AssertTrue(t, yar.IsZero(), yar.String())
+}
+
+func TestChartGetBackgroundStyle(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Background: Style{
+			FillColor: drawing.ColorBlack,
+		},
+	}
+
+	bs := c.getBackgroundStyle()
+	testutil.AssertEqual(t, bs.FillColor.String(), drawing.ColorBlack.String())
+}
+
+func TestChartGetCanvasStyle(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Canvas: Style{
+			FillColor: drawing.ColorBlack,
+		},
+	}
+
+	bs := c.getCanvasStyle()
+	testutil.AssertEqual(t, bs.FillColor.String(), drawing.ColorBlack.String())
+}
+
+func TestChartGetDefaultCanvasBox(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{}
+	canvasBoxDefault := c.getDefaultCanvasBox()
+	testutil.AssertFalse(t, canvasBoxDefault.IsZero())
+	testutil.AssertEqual(t, DefaultBackgroundPadding.Top, canvasBoxDefault.Top)
+	testutil.AssertEqual(t, DefaultBackgroundPadding.Left, canvasBoxDefault.Left)
+	testutil.AssertEqual(t, c.GetWidth()-DefaultBackgroundPadding.Right, canvasBoxDefault.Right)
+	testutil.AssertEqual(t, c.GetHeight()-DefaultBackgroundPadding.Bottom, canvasBoxDefault.Bottom)
+
+	custom := Chart{
+		Background: Style{
+			Padding: Box{
+				Top:    DefaultBackgroundPadding.Top + 1,
+				Left:   DefaultBackgroundPadding.Left + 1,
+				Right:  DefaultBackgroundPadding.Right + 1,
+				Bottom: DefaultBackgroundPadding.Bottom + 1,
+			},
+		},
+	}
+	canvasBoxCustom := custom.getDefaultCanvasBox()
+	testutil.AssertFalse(t, canvasBoxCustom.IsZero())
+	testutil.AssertEqual(t, DefaultBackgroundPadding.Top+1, canvasBoxCustom.Top)
+	testutil.AssertEqual(t, DefaultBackgroundPadding.Left+1, canvasBoxCustom.Left)
+	testutil.AssertEqual(t, c.GetWidth()-(DefaultBackgroundPadding.Right+1), canvasBoxCustom.Right)
+	testutil.AssertEqual(t, c.GetHeight()-(DefaultBackgroundPadding.Bottom+1), canvasBoxCustom.Bottom)
+}
+
+func TestChartGetValueFormatters(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{-2.0, -1.0, 0, 1.0, 2.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 4.5},
+			},
+			ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{-2.1, -1.0, 0, 1.0, 2.0},
+			},
+			ContinuousSeries{
+				YAxis:   YAxisSecondary,
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{10.0, 11.0, 12.0, 13.0, 14.0},
+			},
+		},
+	}
+
+	dxf, dyf, dyaf := c.getValueFormatters()
+	testutil.AssertNotNil(t, dxf)
+	testutil.AssertNotNil(t, dyf)
+	testutil.AssertNotNil(t, dyaf)
+}
+
+func TestChartHasAxes(t *testing.T) {
+	// replaced new assertions helper
+
+	testutil.AssertTrue(t, Chart{}.hasAxes())
+	testutil.AssertFalse(t, Chart{XAxis: XAxis{Style: Hidden()}, YAxis: YAxis{Style: Hidden()}, YAxisSecondary: YAxis{Style: Hidden()}}.hasAxes())
+
+	x := Chart{
+		XAxis: XAxis{
+			Style: Hidden(),
+		},
+		YAxis: YAxis{
+			Style: Shown(),
+		},
+		YAxisSecondary: YAxis{
+			Style: Hidden(),
+		},
+	}
+	testutil.AssertTrue(t, x.hasAxes())
+
+	y := Chart{
+		XAxis: XAxis{
+			Style: Shown(),
+		},
+		YAxis: YAxis{
+			Style: Hidden(),
+		},
+		YAxisSecondary: YAxis{
+			Style: Hidden(),
+		},
+	}
+	testutil.AssertTrue(t, y.hasAxes())
+
+	ya := Chart{
+		XAxis: XAxis{
+			Style: Hidden(),
+		},
+		YAxis: YAxis{
+			Style: Hidden(),
+		},
+		YAxisSecondary: YAxis{
+			Style: Shown(),
+		},
+	}
+	testutil.AssertTrue(t, ya.hasAxes())
+}
+
+func TestChartGetAxesTicks(t *testing.T) {
+	// replaced new assertions helper
+
+	r, err := PNG(1024, 1024)
+	testutil.AssertNil(t, err)
+
+	c := Chart{
+		XAxis: XAxis{
+			Range: &ContinuousRange{Min: 9.8, Max: 19.8},
+		},
+		YAxis: YAxis{
+			Range: &ContinuousRange{Min: 9.9, Max: 19.9},
+		},
+		YAxisSecondary: YAxis{
+			Range: &ContinuousRange{Min: 9.7, Max: 19.7},
+		},
+	}
+	xr, yr, yar := c.getRanges()
+
+	xt, yt, yat := c.getAxesTicks(r, xr, yr, yar, FloatValueFormatter, FloatValueFormatter, FloatValueFormatter)
+	testutil.AssertNotEmpty(t, xt)
+	testutil.AssertNotEmpty(t, yt)
+	testutil.AssertNotEmpty(t, yat)
+}
+
+func TestChartSingleSeries(t *testing.T) {
+	// replaced new assertions helper
+	now := time.Now()
+	c := Chart{
+		Title:  "Hello!",
+		Width:  1024,
+		Height: 400,
+		YAxis: YAxis{
+			Range: &ContinuousRange{
+				Min: 0.0,
+				Max: 4.0,
+			},
+		},
+		Series: []Series{
+			TimeSeries{
+				Name:    "goog",
+				XValues: []time.Time{now.AddDate(0, 0, -3), now.AddDate(0, 0, -2), now.AddDate(0, 0, -1)},
+				YValues: []float64{1.0, 2.0, 3.0},
+			},
+		},
+	}
+
+	buffer := bytes.NewBuffer([]byte{})
+	c.Render(PNG, buffer)
+	testutil.AssertNotEmpty(t, buffer.Bytes())
+}
+
+func TestChartRegressionBadRanges(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1)},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 4.5},
+			},
+		},
+	}
+	buffer := bytes.NewBuffer([]byte{})
+	c.Render(PNG, buffer)
+	testutil.AssertTrue(t, true, "Render needs to finish.")
+}
+
+func TestChartRegressionBadRangesByUser(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		YAxis: YAxis{
+			Range: &ContinuousRange{
+				Min: math.Inf(-1),
+				Max: math.Inf(1), // this could really happen? eh.
+			},
+		},
+		Series: []Series{
+			ContinuousSeries{
+				XValues: LinearRange(1.0, 10.0),
+				YValues: LinearRange(1.0, 10.0),
+			},
+		},
+	}
+	buffer := bytes.NewBuffer([]byte{})
+	c.Render(PNG, buffer)
+	testutil.AssertTrue(t, true, "Render needs to finish.")
+}
+
+func TestChartValidatesSeries(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Series: []Series{
+			ContinuousSeries{
+				XValues: LinearRange(1.0, 10.0),
+				YValues: LinearRange(1.0, 10.0),
+			},
+		},
+	}
+
+	testutil.AssertNil(t, c.validateSeries())
+
+	c = Chart{
+		Series: []Series{
+			ContinuousSeries{
+				XValues: LinearRange(1.0, 10.0),
+			},
+		},
+	}
+
+	testutil.AssertNotNil(t, c.validateSeries())
+}
+
+func TestChartCheckRanges(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{1.0, 2.0},
+				YValues: []float64{3.10, 3.14},
+			},
+		},
+	}
+
+	xr, yr, yra := c.getRanges()
+	testutil.AssertNil(t, c.checkRanges(xr, yr, yra))
+}
+
+func TestChartCheckRangesWithRanges(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		XAxis: XAxis{
+			Range: &ContinuousRange{
+				Min: 0,
+				Max: 10,
+			},
+		},
+		YAxis: YAxis{
+			Range: &ContinuousRange{
+				Min: 0,
+				Max: 5,
+			},
+		},
+		Series: []Series{
+			ContinuousSeries{
+				XValues: []float64{1.0, 2.0},
+				YValues: []float64{3.14, 3.14},
+			},
+		},
+	}
+
+	xr, yr, yra := c.getRanges()
+	testutil.AssertNil(t, c.checkRanges(xr, yr, yra))
+}
+
+func at(i image.Image, x, y int) drawing.Color {
+	return drawing.ColorFromAlphaMixedRGBA(i.At(x, y).RGBA())
+}
+
+func TestChartE2ELine(t *testing.T) {
+	// replaced new assertions helper
+
+	c := Chart{
+		Height:         50,
+		Width:          50,
+		TitleStyle:     Hidden(),
+		XAxis:          HideXAxis(),
+		YAxis:          HideYAxis(),
+		YAxisSecondary: HideYAxis(),
+		Canvas: Style{
+			Padding: BoxZero,
+		},
+		Background: Style{
+			Padding: BoxZero,
+		},
+		Series: []Series{
+			ContinuousSeries{
+				XValues: LinearRangeWithStep(0, 4, 1),
+				YValues: LinearRangeWithStep(0, 4, 1),
+			},
+		},
+	}
+
+	var buffer = &bytes.Buffer{}
+	err := c.Render(PNG, buffer)
+	testutil.AssertNil(t, err)
+
+	// do color tests ...
+
+	i, err := png.Decode(buffer)
+	testutil.AssertNil(t, err)
+
+	// test the bottom and top of the line
+	testutil.AssertEqual(t, drawing.ColorWhite, at(i, 0, 0))
+	testutil.AssertEqual(t, drawing.ColorWhite, at(i, 49, 49))
+
+	// test a line mid point
+	defaultSeriesColor := GetDefaultColor(0)
+	testutil.AssertEqual(t, defaultSeriesColor, at(i, 0, 49))
+	testutil.AssertEqual(t, defaultSeriesColor, at(i, 49, 0))
+	testutil.AssertEqual(t, drawing.ColorFromHex("bddbf6"), at(i, 24, 24))
+}
+
+func TestChartE2ELineWithFill(t *testing.T) {
+	// replaced new assertions helper
+
+	logBuffer := new(bytes.Buffer)
+
+	c := Chart{
+		Height: 50,
+		Width:  50,
+		Canvas: Style{
+			Padding: BoxZero,
+		},
+		Background: Style{
+			Padding: BoxZero,
+		},
+		TitleStyle:     Hidden(),
+		XAxis:          HideXAxis(),
+		YAxis:          HideYAxis(),
+		YAxisSecondary: HideYAxis(),
+		Series: []Series{
+			ContinuousSeries{
+				Style: Style{
+					StrokeColor: drawing.ColorBlue,
+					FillColor:   drawing.ColorRed,
+				},
+				XValues: LinearRangeWithStep(0, 4, 1),
+				YValues: LinearRangeWithStep(0, 4, 1),
+			},
+		},
+		Log: NewLogger(OptLoggerStdout(logBuffer), OptLoggerStderr(logBuffer)),
+	}
+
+	testutil.AssertEqual(t, 5, len(c.Series[0].(ContinuousSeries).XValues))
+	testutil.AssertEqual(t, 5, len(c.Series[0].(ContinuousSeries).YValues))
+
+	var buffer = &bytes.Buffer{}
+	err := c.Render(PNG, buffer)
+	testutil.AssertNil(t, err)
+
+	i, err := png.Decode(buffer)
+	testutil.AssertNil(t, err)
+
+	// test the bottom and top of the line
+	testutil.AssertEqual(t, drawing.ColorWhite, at(i, 0, 0))
+	testutil.AssertEqual(t, drawing.ColorRed, at(i, 49, 49))
+
+	// test a line mid point
+	defaultSeriesColor := drawing.ColorBlue
+	testutil.AssertEqual(t, defaultSeriesColor, at(i, 0, 49))
+	testutil.AssertEqual(t, defaultSeriesColor, at(i, 49, 0))
+}
+
+func Test_Chart_cve(t *testing.T) {
+	poc := StackedBarChart{
+		Title: "poc",
+		Bars: []StackedBar{
+			{
+				Name: "11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111",
+				Values: []Value{
+					{Value: 1, Label: "infinite"},
+					{Value: 1, Label: "loop"},
+				},
+			},
+		},
+	}
+
+	var imgContent bytes.Buffer
+	err := poc.Render(PNG, &imgContent)
+	testutil.AssertNotNil(t, err)
+}

cmd/chart/main.go

@@ -0,0 +1,148 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+var (
+	outputPath = flag.String("output", "", "The output file")
+
+	inputFormat = flag.String("format", "csv", "The input format, either 'csv' or 'tsv' (defaults to 'csv')")
+	inputPath   = flag.String("f", "", "The input file")
+	reverse     = flag.Bool("reverse", false, "If we should reverse the inputs")
+
+	hideLegend     = flag.Bool("hide-legend", false, "If we should omit the chart legend")
+	hideSMA        = flag.Bool("hide-sma", false, "If we should omit simple moving average")
+	hideLinreg     = flag.Bool("hide-linreg", false, "If we should omit linear regressions")
+	hideLastValues = flag.Bool("hide-last-values", false, "If we should omit last values")
+)
+
+func main() {
+	flag.Parse()
+	log := chart.NewLogger()
+
+	var rawData []byte
+	var err error
+	if *inputPath != "" {
+		if *inputPath == "-" {
+			rawData, err = ioutil.ReadAll(os.Stdin)
+			if err != nil {
+				log.FatalErr(err)
+			}
+		} else {
+			rawData, err = ioutil.ReadFile(*inputPath)
+			if err != nil {
+				log.FatalErr(err)
+			}
+		}
+	} else if len(flag.Args()) > 0 {
+		rawData = []byte(flag.Args()[0])
+	} else {
+		flag.Usage()
+		os.Exit(1)
+	}
+
+	var parts []string
+	switch *inputFormat {
+	case "csv":
+		parts = chart.SplitCSV(string(rawData))
+	case "tsv":
+		parts = strings.Split(string(rawData), "\t")
+	default:
+		log.FatalErr(fmt.Errorf("invalid format; must be 'csv' or 'tsv'"))
+	}
+
+	yvalues, err := chart.ParseFloats(parts...)
+	if err != nil {
+		log.FatalErr(err)
+	}
+
+	if *reverse {
+		yvalues = chart.ValueSequence(yvalues...).Reverse().Values()
+	}
+
+	var series []chart.Series
+	mainSeries := chart.ContinuousSeries{
+		Name:    "Values",
+		XValues: chart.LinearRange(1, float64(len(yvalues))),
+		YValues: yvalues,
+	}
+	series = append(series, mainSeries)
+
+	smaSeries := &chart.SMASeries{
+		Name: "SMA",
+		Style: chart.Style{
+			Hidden:          *hideSMA,
+			StrokeColor:     chart.ColorRed,
+			StrokeDashArray: []float64{5.0, 5.0},
+		},
+		InnerSeries: mainSeries,
+	}
+	series = append(series, smaSeries)
+
+	linRegSeries := &chart.LinearRegressionSeries{
+		Name: "Values - Lin. Reg.",
+		Style: chart.Style{
+			Hidden: *hideLinreg,
+		},
+		InnerSeries: mainSeries,
+	}
+	series = append(series, linRegSeries)
+
+	mainLastValue := chart.LastValueAnnotationSeries(mainSeries)
+	mainLastValue.Style = chart.Style{
+		Hidden: *hideLastValues,
+	}
+	series = append(series, mainLastValue)
+
+	linregLastValue := chart.LastValueAnnotationSeries(linRegSeries)
+	linregLastValue.Style = chart.Style{
+		Hidden: (*hideLastValues || *hideLinreg),
+	}
+	series = append(series, linregLastValue)
+
+	smaLastValue := chart.LastValueAnnotationSeries(smaSeries)
+	smaLastValue.Style = chart.Style{
+		Hidden: (*hideLastValues || *hideSMA),
+	}
+	series = append(series, smaLastValue)
+
+	graph := chart.Chart{
+		Background: chart.Style{
+			Padding: chart.Box{
+				Top: 50,
+			},
+		},
+		Series: series,
+	}
+
+	if !*hideLegend {
+		graph.Elements = []chart.Renderable{chart.LegendThin(&graph)}
+	}
+
+	var output *os.File
+	if *outputPath != "" {
+		output, err = os.Create(*outputPath)
+		if err != nil {
+			log.FatalErr(err)
+		}
+	} else {
+		output, err = ioutil.TempFile("", "*.png")
+		if err != nil {
+			log.FatalErr(err)
+		}
+	}
+
+	if err := graph.Render(chart.PNG, output); err != nil {
+		log.FatalErr(err)
+	}
+
+	fmt.Fprintln(os.Stdout, output.Name())
+	os.Exit(0)
+}

colors.go

@@ -0,0 +1,184 @@
+package chart
+
+import "github.com/wcharczuk/go-chart/v2/drawing"
+
+var (
+	// ColorWhite is white.
+	ColorWhite = drawing.Color{R: 255, G: 255, B: 255, A: 255}
+	// ColorBlue is the basic theme blue color.
+	ColorBlue = drawing.Color{R: 0, G: 116, B: 217, A: 255}
+	// ColorCyan is the basic theme cyan color.
+	ColorCyan = drawing.Color{R: 0, G: 217, B: 210, A: 255}
+	// ColorGreen is the basic theme green color.
+	ColorGreen = drawing.Color{R: 0, G: 217, B: 101, A: 255}
+	// ColorRed is the basic theme red color.
+	ColorRed = drawing.Color{R: 217, G: 0, B: 116, A: 255}
+	// ColorOrange is the basic theme orange color.
+	ColorOrange = drawing.Color{R: 217, G: 101, B: 0, A: 255}
+	// ColorYellow is the basic theme yellow color.
+	ColorYellow = drawing.Color{R: 217, G: 210, B: 0, A: 255}
+	// ColorBlack is the basic theme black color.
+	ColorBlack = drawing.Color{R: 51, G: 51, B: 51, A: 255}
+	// ColorLightGray is the basic theme light gray color.
+	ColorLightGray = drawing.Color{R: 239, G: 239, B: 239, A: 255}
+
+	// ColorAlternateBlue is a alternate theme color.
+	ColorAlternateBlue = drawing.Color{R: 106, G: 195, B: 203, A: 255}
+	// ColorAlternateGreen is a alternate theme color.
+	ColorAlternateGreen = drawing.Color{R: 42, G: 190, B: 137, A: 255}
+	// ColorAlternateGray is a alternate theme color.
+	ColorAlternateGray = drawing.Color{R: 110, G: 128, B: 139, A: 255}
+	// ColorAlternateYellow is a alternate theme color.
+	ColorAlternateYellow = drawing.Color{R: 240, G: 174, B: 90, A: 255}
+	// ColorAlternateLightGray is a alternate theme color.
+	ColorAlternateLightGray = drawing.Color{R: 187, G: 190, B: 191, A: 255}
+
+	// ColorTransparent is a transparent (alpha zero) color.
+	ColorTransparent = drawing.Color{R: 1, G: 1, B: 1, A: 0}
+)
+
+var (
+	// DefaultBackgroundColor is the default chart background color.
+	// It is equivalent to css color:white.
+	DefaultBackgroundColor = ColorWhite
+	// DefaultBackgroundStrokeColor is the default chart border color.
+	// It is equivalent to color:white.
+	DefaultBackgroundStrokeColor = ColorWhite
+	// DefaultCanvasColor is the default chart canvas color.
+	// It is equivalent to css color:white.
+	DefaultCanvasColor = ColorWhite
+	// DefaultCanvasStrokeColor is the default chart canvas stroke color.
+	// It is equivalent to css color:white.
+	DefaultCanvasStrokeColor = ColorWhite
+	// DefaultTextColor is the default chart text color.
+	// It is equivalent to #333333.
+	DefaultTextColor = ColorBlack
+	// DefaultAxisColor is the default chart axis line color.
+	// It is equivalent to #333333.
+	DefaultAxisColor = ColorBlack
+	// DefaultStrokeColor is the default chart border color.
+	// It is equivalent to #efefef.
+	DefaultStrokeColor = ColorLightGray
+	// DefaultFillColor is the default fill color.
+	// It is equivalent to #0074d9.
+	DefaultFillColor = ColorBlue
+	// DefaultAnnotationFillColor is the default annotation background color.
+	DefaultAnnotationFillColor = ColorWhite
+	// DefaultGridLineColor is the default grid line color.
+	DefaultGridLineColor = ColorLightGray
+)
+
+var (
+	// DefaultColors are a couple default series colors.
+	DefaultColors = []drawing.Color{
+		ColorBlue,
+		ColorGreen,
+		ColorRed,
+		ColorCyan,
+		ColorOrange,
+	}
+
+	// DefaultAlternateColors are a couple alternate colors.
+	DefaultAlternateColors = []drawing.Color{
+		ColorAlternateBlue,
+		ColorAlternateGreen,
+		ColorAlternateGray,
+		ColorAlternateYellow,
+		ColorBlue,
+		ColorGreen,
+		ColorRed,
+		ColorCyan,
+		ColorOrange,
+	}
+)
+
+// GetDefaultColor returns a color from the default list by index.
+// NOTE: the index will wrap around (using a modulo).
+func GetDefaultColor(index int) drawing.Color {
+	finalIndex := index % len(DefaultColors)
+	return DefaultColors[finalIndex]
+}
+
+// GetAlternateColor returns a color from the default list by index.
+// NOTE: the index will wrap around (using a modulo).
+func GetAlternateColor(index int) drawing.Color {
+	finalIndex := index % len(DefaultAlternateColors)
+	return DefaultAlternateColors[finalIndex]
+}
+
+// ColorPalette is a set of colors that.
+type ColorPalette interface {
+	BackgroundColor() drawing.Color
+	BackgroundStrokeColor() drawing.Color
+	CanvasColor() drawing.Color
+	CanvasStrokeColor() drawing.Color
+	AxisStrokeColor() drawing.Color
+	TextColor() drawing.Color
+	GetSeriesColor(index int) drawing.Color
+}
+
+// DefaultColorPalette represents the default palatte.
+var DefaultColorPalette defaultColorPalette
+
+type defaultColorPalette struct{}
+
+func (dp defaultColorPalette) BackgroundColor() drawing.Color {
+	return DefaultBackgroundColor
+}
+
+func (dp defaultColorPalette) BackgroundStrokeColor() drawing.Color {
+	return DefaultBackgroundStrokeColor
+}
+
+func (dp defaultColorPalette) CanvasColor() drawing.Color {
+	return DefaultCanvasColor
+}
+
+func (dp defaultColorPalette) CanvasStrokeColor() drawing.Color {
+	return DefaultCanvasStrokeColor
+}
+
+func (dp defaultColorPalette) AxisStrokeColor() drawing.Color {
+	return DefaultAxisColor
+}
+
+func (dp defaultColorPalette) TextColor() drawing.Color {
+	return DefaultTextColor
+}
+
+func (dp defaultColorPalette) GetSeriesColor(index int) drawing.Color {
+	return GetDefaultColor(index)
+}
+
+// AlternateColorPalette represents the default palatte.
+var AlternateColorPalette alternateColorPalette
+
+type alternateColorPalette struct{}
+
+func (ap alternateColorPalette) BackgroundColor() drawing.Color {
+	return DefaultBackgroundColor
+}
+
+func (ap alternateColorPalette) BackgroundStrokeColor() drawing.Color {
+	return DefaultBackgroundStrokeColor
+}
+
+func (ap alternateColorPalette) CanvasColor() drawing.Color {
+	return DefaultCanvasColor
+}
+
+func (ap alternateColorPalette) CanvasStrokeColor() drawing.Color {
+	return DefaultCanvasStrokeColor
+}
+
+func (ap alternateColorPalette) AxisStrokeColor() drawing.Color {
+	return DefaultAxisColor
+}
+
+func (ap alternateColorPalette) TextColor() drawing.Color {
+	return DefaultTextColor
+}
+
+func (ap alternateColorPalette) GetSeriesColor(index int) drawing.Color {
+	return GetAlternateColor(index)
+}

concat_series.go

@@ -0,0 +1,44 @@
+package chart
+
+// ConcatSeries is a special type of series that concatenates its `InnerSeries`.
+type ConcatSeries []Series
+
+// Len returns the length of the concatenated set of series.
+func (cs ConcatSeries) Len() int {
+	total := 0
+	for _, s := range cs {
+		if typed, isValuesProvider := s.(ValuesProvider); isValuesProvider {
+			total += typed.Len()
+		}
+	}
+
+	return total
+}
+
+// GetValue returns the value at the (meta) index (i.e 0 => totalLen-1)
+func (cs ConcatSeries) GetValue(index int) (x, y float64) {
+	cursor := 0
+	for _, s := range cs {
+		if typed, isValuesProvider := s.(ValuesProvider); isValuesProvider {
+			len := typed.Len()
+			if index < cursor+len {
+				x, y = typed.GetValues(index - cursor) //FENCEPOSTS.
+				return
+			}
+			cursor += typed.Len()
+		}
+	}
+	return
+}
+
+// Validate validates the series.
+func (cs ConcatSeries) Validate() error {
+	var err error
+	for _, s := range cs {
+		err = s.Validate()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}

concat_series_test.go

@@ -0,0 +1,41 @@
+package chart
+
+import (
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestConcatSeries(t *testing.T) {
+	// replaced new assertions helper
+
+	s1 := ContinuousSeries{
+		XValues: LinearRange(1.0, 10.0),
+		YValues: LinearRange(1.0, 10.0),
+	}
+
+	s2 := ContinuousSeries{
+		XValues: LinearRange(11, 20.0),
+		YValues: LinearRange(10.0, 1.0),
+	}
+
+	s3 := ContinuousSeries{
+		XValues: LinearRange(21, 30.0),
+		YValues: LinearRange(1.0, 10.0),
+	}
+
+	cs := ConcatSeries([]Series{s1, s2, s3})
+	testutil.AssertEqual(t, 30, cs.Len())
+
+	x0, y0 := cs.GetValue(0)
+	testutil.AssertEqual(t, 1.0, x0)
+	testutil.AssertEqual(t, 1.0, y0)
+
+	xm, ym := cs.GetValue(19)
+	testutil.AssertEqual(t, 20.0, xm)
+	testutil.AssertEqual(t, 1.0, ym)
+
+	xn, yn := cs.GetValue(29)
+	testutil.AssertEqual(t, 30.0, xn)
+	testutil.AssertEqual(t, 10.0, yn)
+}

continuous_range.go

@@ -0,0 +1,81 @@
+package chart
+
+import (
+	"fmt"
+	"math"
+)
+
+// ContinuousRange represents a boundary for a set of numbers.
+type ContinuousRange struct {
+	Min        float64
+	Max        float64
+	Domain     int
+	Descending bool
+}
+
+// IsDescending returns if the range is descending.
+func (r ContinuousRange) IsDescending() bool {
+	return r.Descending
+}
+
+// IsZero returns if the ContinuousRange has been set or not.
+func (r ContinuousRange) IsZero() bool {
+	return (r.Min == 0 || math.IsNaN(r.Min)) &&
+		(r.Max == 0 || math.IsNaN(r.Max)) &&
+		r.Domain == 0
+}
+
+// GetMin gets the min value for the continuous range.
+func (r ContinuousRange) GetMin() float64 {
+	return r.Min
+}
+
+// SetMin sets the min value for the continuous range.
+func (r *ContinuousRange) SetMin(min float64) {
+	r.Min = min
+}
+
+// GetMax returns the max value for the continuous range.
+func (r ContinuousRange) GetMax() float64 {
+	return r.Max
+}
+
+// SetMax sets the max value for the continuous range.
+func (r *ContinuousRange) SetMax(max float64) {
+	r.Max = max
+}
+
+// GetDelta returns the difference between the min and max value.
+func (r ContinuousRange) GetDelta() float64 {
+	return r.Max - r.Min
+}
+
+// GetDomain returns the range domain.
+func (r ContinuousRange) GetDomain() int {
+	return r.Domain
+}
+
+// SetDomain sets the range domain.
+func (r *ContinuousRange) SetDomain(domain int) {
+	r.Domain = domain
+}
+
+// String returns a simple string for the ContinuousRange.
+func (r ContinuousRange) String() string {
+	if r.GetDelta() == 0 {
+		return "ContinuousRange [empty]"
+	}
+	return fmt.Sprintf("ContinuousRange [%.2f,%.2f] => %d", r.Min, r.Max, r.Domain)
+}
+
+// Translate maps a given value into the ContinuousRange space.
+func (r ContinuousRange) Translate(value float64) int {
+	normalized := value - r.Min
+	ratio := normalized / r.GetDelta()
+
+	if r.IsDescending() {
+		return r.Domain - int(math.Ceil(ratio*float64(r.Domain)))
+	}
+
+	return int(math.Ceil(ratio * float64(r.Domain)))
+}

continuous_range_test.go

@@ -0,0 +1,22 @@
+package chart
+
+import (
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestRangeTranslate(t *testing.T) {
+	// replaced new assertions helper
+	values := []float64{1.0, 2.0, 2.5, 2.7, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0}
+	r := ContinuousRange{Domain: 1000}
+	r.Min, r.Max = MinMax(values...)
+
+	// delta = ~7.0
+	// value = ~5.0
+	// domain = ~1000
+	// 5/8 * 1000 ~=
+	testutil.AssertEqual(t, 0, r.Translate(1.0))
+	testutil.AssertEqual(t, 1000, r.Translate(8.0))
+	testutil.AssertEqual(t, 572, r.Translate(5.0))
+}

continuous_series.go

@@ -0,0 +1,96 @@
+package chart
+
+import "fmt"
+
+// Interface Assertions.
+var (
+	_ Series              = (*ContinuousSeries)(nil)
+	_ FirstValuesProvider = (*ContinuousSeries)(nil)
+	_ LastValuesProvider  = (*ContinuousSeries)(nil)
+)
+
+// ContinuousSeries represents a line on a chart.
+type ContinuousSeries struct {
+	Name  string
+	Style Style
+
+	YAxis YAxisType
+
+	XValueFormatter ValueFormatter
+	YValueFormatter ValueFormatter
+
+	XValues []float64
+	YValues []float64
+}
+
+// GetName returns the name of the time series.
+func (cs ContinuousSeries) GetName() string {
+	return cs.Name
+}
+
+// GetStyle returns the line style.
+func (cs ContinuousSeries) GetStyle() Style {
+	return cs.Style
+}
+
+// Len returns the number of elements in the series.
+func (cs ContinuousSeries) Len() int {
+	return len(cs.XValues)
+}
+
+// GetValues gets the x,y values at a given index.
+func (cs ContinuousSeries) GetValues(index int) (float64, float64) {
+	return cs.XValues[index], cs.YValues[index]
+}
+
+// GetFirstValues gets the first x,y values.
+func (cs ContinuousSeries) GetFirstValues() (float64, float64) {
+	return cs.XValues[0], cs.YValues[0]
+}
+
+// GetLastValues gets the last x,y values.
+func (cs ContinuousSeries) GetLastValues() (float64, float64) {
+	return cs.XValues[len(cs.XValues)-1], cs.YValues[len(cs.YValues)-1]
+}
+
+// GetValueFormatters returns value formatter defaults for the series.
+func (cs ContinuousSeries) GetValueFormatters() (x, y ValueFormatter) {
+	if cs.XValueFormatter != nil {
+		x = cs.XValueFormatter
+	} else {
+		x = FloatValueFormatter
+	}
+	if cs.YValueFormatter != nil {
+		y = cs.YValueFormatter
+	} else {
+		y = FloatValueFormatter
+	}
+	return
+}
+
+// GetYAxis returns which YAxis the series draws on.
+func (cs ContinuousSeries) GetYAxis() YAxisType {
+	return cs.YAxis
+}
+
+// Render renders the series.
+func (cs ContinuousSeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) {
+	style := cs.Style.InheritFrom(defaults)
+	Draw.LineSeries(r, canvasBox, xrange, yrange, style, cs)
+}
+
+// Validate validates the series.
+func (cs ContinuousSeries) Validate() error {
+	if len(cs.XValues) == 0 {
+		return fmt.Errorf("continuous series; must have xvalues set")
+	}
+
+	if len(cs.YValues) == 0 {
+		return fmt.Errorf("continuous series; must have yvalues set")
+	}
+
+	if len(cs.XValues) != len(cs.YValues) {
+		return fmt.Errorf("continuous series; must have same length xvalues as yvalues")
+	}
+	return nil
+}

continuous_series_test.go

@@ -0,0 +1,72 @@
+package chart
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestContinuousSeries(t *testing.T) {
+	// replaced new assertions helper
+
+	cs := ContinuousSeries{
+		Name:    "Test Series",
+		XValues: LinearRange(1.0, 10.0),
+		YValues: LinearRange(1.0, 10.0),
+	}
+
+	testutil.AssertEqual(t, "Test Series", cs.GetName())
+	testutil.AssertEqual(t, 10, cs.Len())
+	x0, y0 := cs.GetValues(0)
+	testutil.AssertEqual(t, 1.0, x0)
+	testutil.AssertEqual(t, 1.0, y0)
+
+	xn, yn := cs.GetValues(9)
+	testutil.AssertEqual(t, 10.0, xn)
+	testutil.AssertEqual(t, 10.0, yn)
+
+	xn, yn = cs.GetLastValues()
+	testutil.AssertEqual(t, 10.0, xn)
+	testutil.AssertEqual(t, 10.0, yn)
+}
+
+func TestContinuousSeriesValueFormatter(t *testing.T) {
+	// replaced new assertions helper
+
+	cs := ContinuousSeries{
+		XValueFormatter: func(v interface{}) string {
+			return fmt.Sprintf("%f foo", v)
+		},
+		YValueFormatter: func(v interface{}) string {
+			return fmt.Sprintf("%f bar", v)
+		},
+	}
+
+	xf, yf := cs.GetValueFormatters()
+	testutil.AssertEqual(t, "0.100000 foo", xf(0.1))
+	testutil.AssertEqual(t, "0.100000 bar", yf(0.1))
+}
+
+func TestContinuousSeriesValidate(t *testing.T) {
+	// replaced new assertions helper
+
+	cs := ContinuousSeries{
+		Name:    "Test Series",
+		XValues: LinearRange(1.0, 10.0),
+		YValues: LinearRange(1.0, 10.0),
+	}
+	testutil.AssertNil(t, cs.Validate())
+
+	cs = ContinuousSeries{
+		Name:    "Test Series",
+		XValues: LinearRange(1.0, 10.0),
+	}
+	testutil.AssertNotNil(t, cs.Validate())
+
+	cs = ContinuousSeries{
+		Name:    "Test Series",
+		YValues: LinearRange(1.0, 10.0),
+	}
+	testutil.AssertNotNil(t, cs.Validate())
+}

defaults.go

@@ -0,0 +1,103 @@
+package chart
+
+const (
+	// DefaultChartHeight is the default chart height.
+	DefaultChartHeight = 400
+	// DefaultChartWidth is the default chart width.
+	DefaultChartWidth = 1024
+	// DefaultStrokeWidth is the default chart stroke width.
+	DefaultStrokeWidth = 0.0
+	// DefaultDotWidth is the default chart dot width.
+	DefaultDotWidth = 0.0
+	// DefaultSeriesLineWidth is the default line width.
+	DefaultSeriesLineWidth = 1.0
+	// DefaultAxisLineWidth is the line width of the axis lines.
+	DefaultAxisLineWidth = 1.0
+	//DefaultDPI is the default dots per inch for the chart.
+	DefaultDPI = 92.0
+	// DefaultMinimumFontSize is the default minimum font size.
+	DefaultMinimumFontSize = 8.0
+	// DefaultFontSize is the default font size.
+	DefaultFontSize = 10.0
+	// DefaultTitleFontSize is the default title font size.
+	DefaultTitleFontSize = 18.0
+	// DefaultAnnotationDeltaWidth is the width of the left triangle out of annotations.
+	DefaultAnnotationDeltaWidth = 10
+	// DefaultAnnotationFontSize is the font size of annotations.
+	DefaultAnnotationFontSize = 10.0
+	// DefaultAxisFontSize is the font size of the axis labels.
+	DefaultAxisFontSize = 10.0
+	// DefaultTitleTop is the default distance from the top of the chart to put the title.
+	DefaultTitleTop = 10
+
+	// DefaultBackgroundStrokeWidth is the default stroke on the chart background.
+	DefaultBackgroundStrokeWidth = 0.0
+	// DefaultCanvasStrokeWidth is the default stroke on the chart canvas.
+	DefaultCanvasStrokeWidth = 0.0
+
+	// DefaultLineSpacing is the default vertical distance between lines of text.
+	DefaultLineSpacing = 5
+
+	// DefaultYAxisMargin is the default distance from the right of the canvas to the y axis labels.
+	DefaultYAxisMargin = 10
+	// DefaultXAxisMargin is the default distance from bottom of the canvas to the x axis labels.
+	DefaultXAxisMargin = 10
+
+	//DefaultVerticalTickHeight is half the margin.
+	DefaultVerticalTickHeight = DefaultXAxisMargin >> 1
+	//DefaultHorizontalTickWidth is half the margin.
+	DefaultHorizontalTickWidth = DefaultYAxisMargin >> 1
+
+	// DefaultTickCount is the default number of ticks to show
+	DefaultTickCount = 10
+	// DefaultTickCountSanityCheck is a hard limit on number of ticks to prevent infinite loops.
+	DefaultTickCountSanityCheck = 1 << 10 //1024
+
+	// DefaultMinimumTickHorizontalSpacing is the minimum distance between horizontal ticks.
+	DefaultMinimumTickHorizontalSpacing = 20
+	// DefaultMinimumTickVerticalSpacing is the minimum distance between vertical ticks.
+	DefaultMinimumTickVerticalSpacing = 20
+
+	// DefaultDateFormat is the default date format.
+	DefaultDateFormat = "2006-01-02"
+	// DefaultDateHourFormat is the date format for hour timestamp formats.
+	DefaultDateHourFormat = "01-02 3PM"
+	// DefaultDateMinuteFormat is the date format for minute range timestamp formats.
+	DefaultDateMinuteFormat = "01-02 3:04PM"
+	// DefaultFloatFormat is the default float format.
+	DefaultFloatFormat = "%.2f"
+	// DefaultPercentValueFormat is the default percent format.
+	DefaultPercentValueFormat = "%0.2f%%"
+
+	// DefaultBarSpacing is the default pixel spacing between bars.
+	DefaultBarSpacing = 100
+	// DefaultBarWidth is the default pixel width of bars in a bar chart.
+	DefaultBarWidth = 50
+)
+
+var (
+	// DashArrayDots is a dash array that represents '....' style stroke dashes.
+	DashArrayDots = []int{1, 1}
+	// DashArrayDashesSmall is a dash array that represents '- - -' style stroke dashes.
+	DashArrayDashesSmall = []int{3, 3}
+	// DashArrayDashesMedium is a dash array that represents '-- -- --' style stroke dashes.
+	DashArrayDashesMedium = []int{5, 5}
+	// DashArrayDashesLarge is a dash array that represents '----- ----- -----' style stroke dashes.
+	DashArrayDashesLarge = []int{10, 10}
+)
+
+var (
+	// DefaultAnnotationPadding is the padding around an annotation.
+	DefaultAnnotationPadding = Box{Top: 5, Left: 5, Right: 5, Bottom: 5}
+
+	// DefaultBackgroundPadding is the default canvas padding config.
+	DefaultBackgroundPadding = Box{Top: 5, Left: 5, Right: 5, Bottom: 5}
+)
+
+const (
+	// ContentTypePNG is the png mime type.
+	ContentTypePNG = "image/png"
+
+	// ContentTypeSVG is the svg mime type.
+	ContentTypeSVG = "image/svg+xml"
+)

donut_chart.go

@@ -0,0 +1,315 @@
+package chart
+
+import (
+	"errors"
+	"fmt"
+	"io"
+
+	"github.com/golang/freetype/truetype"
+)
+
+// DonutChart is a chart that draws sections of a circle based on percentages with an hole.
+type DonutChart struct {
+	Title      string
+	TitleStyle Style
+
+	ColorPalette ColorPalette
+
+	Width  int
+	Height int
+	DPI    float64
+
+	Background Style
+	Canvas     Style
+	SliceStyle Style
+
+	Font        *truetype.Font
+	defaultFont *truetype.Font
+
+	Values   []Value
+	Elements []Renderable
+}
+
+// GetDPI returns the dpi for the chart.
+func (pc DonutChart) GetDPI(defaults ...float64) float64 {
+	if pc.DPI == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return DefaultDPI
+	}
+	return pc.DPI
+}
+
+// GetFont returns the text font.
+func (pc DonutChart) GetFont() *truetype.Font {
+	if pc.Font == nil {
+		return pc.defaultFont
+	}
+	return pc.Font
+}
+
+// GetWidth returns the chart width or the default value.
+func (pc DonutChart) GetWidth() int {
+	if pc.Width == 0 {
+		return DefaultChartWidth
+	}
+	return pc.Width
+}
+
+// GetHeight returns the chart height or the default value.
+func (pc DonutChart) GetHeight() int {
+	if pc.Height == 0 {
+		return DefaultChartWidth
+	}
+	return pc.Height
+}
+
+// Render renders the chart with the given renderer to the given io.Writer.
+func (pc DonutChart) Render(rp RendererProvider, w io.Writer) error {
+	if len(pc.Values) == 0 {
+		return errors.New("please provide at least one value")
+	}
+
+	r, err := rp(pc.GetWidth(), pc.GetHeight())
+	if err != nil {
+		return err
+	}
+
+	if pc.Font == nil {
+		defaultFont, err := GetDefaultFont()
+		if err != nil {
+			return err
+		}
+		pc.defaultFont = defaultFont
+	}
+	r.SetDPI(pc.GetDPI(DefaultDPI))
+
+	canvasBox := pc.getDefaultCanvasBox()
+	canvasBox = pc.getCircleAdjustedCanvasBox(canvasBox)
+
+	pc.drawBackground(r)
+	pc.drawCanvas(r, canvasBox)
+
+	finalValues, err := pc.finalizeValues(pc.Values)
+	if err != nil {
+		return err
+	}
+	pc.drawSlices(r, canvasBox, finalValues)
+	pc.drawTitle(r)
+	for _, a := range pc.Elements {
+		a(r, canvasBox, pc.styleDefaultsElements())
+	}
+
+	return r.Save(w)
+}
+
+func (pc DonutChart) drawBackground(r Renderer) {
+	Draw.Box(r, Box{
+		Right:  pc.GetWidth(),
+		Bottom: pc.GetHeight(),
+	}, pc.getBackgroundStyle())
+}
+
+func (pc DonutChart) drawCanvas(r Renderer, canvasBox Box) {
+	Draw.Box(r, canvasBox, pc.getCanvasStyle())
+}
+
+func (pc DonutChart) drawTitle(r Renderer) {
+	if len(pc.Title) > 0 && !pc.TitleStyle.Hidden {
+		Draw.TextWithin(r, pc.Title, pc.Box(), pc.styleDefaultsTitle())
+	}
+}
+
+func (pc DonutChart) drawSlices(r Renderer, canvasBox Box, values []Value) {
+	cx, cy := canvasBox.Center()
+	diameter := MinInt(canvasBox.Width(), canvasBox.Height())
+	radius := float64(diameter>>1) / 1.1
+	labelRadius := (radius * 2.83) / 3.0
+
+	// draw the donut slices
+	var rads, delta, delta2, total float64
+	var lx, ly int
+
+	if len(values) == 1 {
+		pc.styleDonutChartValue(0).WriteToRenderer(r)
+		r.MoveTo(cx, cy)
+		r.Circle(radius, cx, cy)
+	} else {
+		for index, v := range values {
+			v.Style.InheritFrom(pc.styleDonutChartValue(index)).WriteToRenderer(r)
+			r.MoveTo(cx, cy)
+			rads = PercentToRadians(total)
+			delta = PercentToRadians(v.Value)
+
+			r.ArcTo(cx, cy, (radius / 1.25), (radius / 1.25), rads, delta)
+
+			r.LineTo(cx, cy)
+			r.Close()
+			r.FillStroke()
+			total = total + v.Value
+		}
+	}
+
+	//making the donut hole
+	v := Value{Value: 100, Label: "center"}
+	styletemp := pc.SliceStyle.InheritFrom(Style{
+		StrokeColor: ColorWhite, StrokeWidth: 4.0, FillColor: ColorWhite, FontColor: ColorWhite, //Font:        pc.GetFont(),//FontSize:    pc.getScaledFontSize(),
+	})
+	v.Style.InheritFrom(styletemp).WriteToRenderer(r)
+	r.MoveTo(cx, cy)
+	r.ArcTo(cx, cy, (radius / 3.5), (radius / 3.5), DegreesToRadians(0), DegreesToRadians(359))
+	r.LineTo(cx, cy)
+	r.Close()
+	r.FillStroke()
+
+	// draw the labels
+	total = 0
+	for index, v := range values {
+		v.Style.InheritFrom(pc.styleDonutChartValue(index)).WriteToRenderer(r)
+		if len(v.Label) > 0 {
+			delta2 = PercentToRadians(total + (v.Value / 2.0))
+			delta2 = RadianAdd(delta2, _pi2)
+			lx, ly = CirclePoint(cx, cy, labelRadius, delta2)
+
+			tb := r.MeasureText(v.Label)
+			lx = lx - (tb.Width() >> 1)
+			ly = ly + (tb.Height() >> 1)
+
+			r.Text(v.Label, lx, ly)
+		}
+		total = total + v.Value
+	}
+}
+
+func (pc DonutChart) finalizeValues(values []Value) ([]Value, error) {
+	finalValues := Values(values).Normalize()
+	if len(finalValues) == 0 {
+		return nil, fmt.Errorf("donut chart must contain at least (1) non-zero value")
+	}
+	return finalValues, nil
+}
+
+func (pc DonutChart) getDefaultCanvasBox() Box {
+	return pc.Box()
+}
+
+func (pc DonutChart) getCircleAdjustedCanvasBox(canvasBox Box) Box {
+	circleDiameter := MinInt(canvasBox.Width(), canvasBox.Height())
+
+	square := Box{
+		Right:  circleDiameter,
+		Bottom: circleDiameter,
+	}
+
+	return canvasBox.Fit(square)
+}
+
+func (pc DonutChart) getBackgroundStyle() Style {
+	return pc.Background.InheritFrom(pc.styleDefaultsBackground())
+}
+
+func (pc DonutChart) getCanvasStyle() Style {
+	return pc.Canvas.InheritFrom(pc.styleDefaultsCanvas())
+}
+
+func (pc DonutChart) styleDefaultsCanvas() Style {
+	return Style{
+		FillColor:   pc.GetColorPalette().CanvasColor(),
+		StrokeColor: pc.GetColorPalette().CanvasStrokeColor(),
+		StrokeWidth: DefaultStrokeWidth,
+	}
+}
+
+func (pc DonutChart) styleDefaultsDonutChartValue() Style {
+	return Style{
+		StrokeColor: pc.GetColorPalette().TextColor(),
+		StrokeWidth: 4.0,
+		FillColor:   pc.GetColorPalette().TextColor(),
+	}
+}
+
+func (pc DonutChart) styleDonutChartValue(index int) Style {
+	return pc.SliceStyle.InheritFrom(Style{
+		StrokeColor: ColorWhite,
+		StrokeWidth: 4.0,
+		FillColor:   pc.GetColorPalette().GetSeriesColor(index),
+		FontSize:    pc.getScaledFontSize(),
+		FontColor:   pc.GetColorPalette().TextColor(),
+		Font:        pc.GetFont(),
+	})
+}
+
+func (pc DonutChart) getScaledFontSize() float64 {
+	effectiveDimension := MinInt(pc.GetWidth(), pc.GetHeight())
+	if effectiveDimension >= 2048 {
+		return 48.0
+	} else if effectiveDimension >= 1024 {
+		return 24.0
+	} else if effectiveDimension > 512 {
+		return 18.0
+	} else if effectiveDimension > 256 {
+		return 12.0
+	}
+	return 10.0
+}
+
+func (pc DonutChart) styleDefaultsBackground() Style {
+	return Style{
+		FillColor:   pc.GetColorPalette().BackgroundColor(),
+		StrokeColor: pc.GetColorPalette().BackgroundStrokeColor(),
+		StrokeWidth: DefaultStrokeWidth,
+	}
+}
+
+func (pc DonutChart) styleDefaultsElements() Style {
+	return Style{
+		Font: pc.GetFont(),
+	}
+}
+
+func (pc DonutChart) styleDefaultsTitle() Style {
+	return pc.TitleStyle.InheritFrom(Style{
+		FontColor:           pc.GetColorPalette().TextColor(),
+		Font:                pc.GetFont(),
+		FontSize:            pc.getTitleFontSize(),
+		TextHorizontalAlign: TextHorizontalAlignCenter,
+		TextVerticalAlign:   TextVerticalAlignTop,
+		TextWrap:            TextWrapWord,
+	})
+}
+
+func (pc DonutChart) getTitleFontSize() float64 {
+	effectiveDimension := MinInt(pc.GetWidth(), pc.GetHeight())
+	if effectiveDimension >= 2048 {
+		return 48
+	} else if effectiveDimension >= 1024 {
+		return 24
+	} else if effectiveDimension >= 512 {
+		return 18
+	} else if effectiveDimension >= 256 {
+		return 12
+	}
+	return 10
+}
+
+// GetColorPalette returns the color palette for the chart.
+func (pc DonutChart) GetColorPalette() ColorPalette {
+	if pc.ColorPalette != nil {
+		return pc.ColorPalette
+	}
+	return AlternateColorPalette
+}
+
+// Box returns the chart bounds as a box.
+func (pc DonutChart) Box() Box {
+	dpr := pc.Background.Padding.GetRight(DefaultBackgroundPadding.Right)
+	dpb := pc.Background.Padding.GetBottom(DefaultBackgroundPadding.Bottom)
+
+	return Box{
+		Top:    pc.Background.Padding.GetTop(DefaultBackgroundPadding.Top),
+		Left:   pc.Background.Padding.GetLeft(DefaultBackgroundPadding.Left),
+		Right:  pc.GetWidth() - dpr,
+		Bottom: pc.GetHeight() - dpb,
+	}
+}

donut_chart_test.go

@@ -0,0 +1,69 @@
+package chart
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestDonutChart(t *testing.T) {
+	// replaced new assertions helper
+
+	pie := DonutChart{
+		Canvas: Style{
+			FillColor: ColorLightGray,
+		},
+		Values: []Value{
+			{Value: 10, Label: "Blue"},
+			{Value: 9, Label: "Green"},
+			{Value: 8, Label: "Gray"},
+			{Value: 7, Label: "Orange"},
+			{Value: 6, Label: "HEANG"},
+			{Value: 5, Label: "??"},
+			{Value: 2, Label: "!!"},
+		},
+	}
+
+	b := bytes.NewBuffer([]byte{})
+	pie.Render(PNG, b)
+	testutil.AssertNotZero(t, b.Len())
+}
+
+func TestDonutChartDropsZeroValues(t *testing.T) {
+	// replaced new assertions helper
+
+	pie := DonutChart{
+		Canvas: Style{
+			FillColor: ColorLightGray,
+		},
+		Values: []Value{
+			{Value: 5, Label: "Blue"},
+			{Value: 5, Label: "Green"},
+			{Value: 0, Label: "Gray"},
+		},
+	}
+
+	b := bytes.NewBuffer([]byte{})
+	err := pie.Render(PNG, b)
+	testutil.AssertNil(t, err)
+}
+
+func TestDonutChartAllZeroValues(t *testing.T) {
+	// replaced new assertions helper
+
+	pie := DonutChart{
+		Canvas: Style{
+			FillColor: ColorLightGray,
+		},
+		Values: []Value{
+			{Value: 0, Label: "Blue"},
+			{Value: 0, Label: "Green"},
+			{Value: 0, Label: "Gray"},
+		},
+	}
+
+	b := bytes.NewBuffer([]byte{})
+	err := pie.Render(PNG, b)
+	testutil.AssertNotNil(t, err)
+}

draw.go

@@ -0,0 +1,325 @@
+package chart
+
+import (
+	"math"
+)
+
+var (
+	// Draw contains helpers for drawing common objects.
+	Draw = &draw{}
+)
+
+type draw struct{}
+
+// LineSeries draws a line series with a renderer.
+func (d draw) LineSeries(r Renderer, canvasBox Box, xrange, yrange Range, style Style, vs ValuesProvider) {
+	if vs.Len() == 0 {
+		return
+	}
+
+	cb := canvasBox.Bottom
+	cl := canvasBox.Left
+
+	v0x, v0y := vs.GetValues(0)
+	x0 := cl + xrange.Translate(v0x)
+	y0 := cb - yrange.Translate(v0y)
+
+	yv0 := yrange.Translate(0)
+
+	var vx, vy float64
+	var x, y int
+
+	if style.ShouldDrawStroke() && style.ShouldDrawFill() {
+		style.GetFillOptions().WriteDrawingOptionsToRenderer(r)
+		r.MoveTo(x0, y0)
+		for i := 1; i < vs.Len(); i++ {
+			vx, vy = vs.GetValues(i)
+			x = cl + xrange.Translate(vx)
+			y = cb - yrange.Translate(vy)
+			r.LineTo(x, y)
+		}
+		r.LineTo(x, MinInt(cb, cb-yv0))
+		r.LineTo(x0, MinInt(cb, cb-yv0))
+		r.LineTo(x0, y0)
+		r.Fill()
+	}
+
+	if style.ShouldDrawStroke() {
+		style.GetStrokeOptions().WriteDrawingOptionsToRenderer(r)
+
+		r.MoveTo(x0, y0)
+		for i := 1; i < vs.Len(); i++ {
+			vx, vy = vs.GetValues(i)
+			x = cl + xrange.Translate(vx)
+			y = cb - yrange.Translate(vy)
+			r.LineTo(x, y)
+		}
+		r.Stroke()
+	}
+
+	if style.ShouldDrawDot() {
+		defaultDotWidth := style.GetDotWidth()
+
+		style.GetDotOptions().WriteDrawingOptionsToRenderer(r)
+		for i := 0; i < vs.Len(); i++ {
+			vx, vy = vs.GetValues(i)
+			x = cl + xrange.Translate(vx)
+			y = cb - yrange.Translate(vy)
+
+			dotWidth := defaultDotWidth
+			if style.DotWidthProvider != nil {
+				dotWidth = style.DotWidthProvider(xrange, yrange, i, vx, vy)
+			}
+
+			if style.DotColorProvider != nil {
+				dotColor := style.DotColorProvider(xrange, yrange, i, vx, vy)
+
+				r.SetFillColor(dotColor)
+				r.SetStrokeColor(dotColor)
+			}
+
+			r.Circle(dotWidth, x, y)
+			r.FillStroke()
+		}
+	}
+}
+
+// BoundedSeries draws a series that implements BoundedValuesProvider.
+func (d draw) BoundedSeries(r Renderer, canvasBox Box, xrange, yrange Range, style Style, bbs BoundedValuesProvider, drawOffsetIndexes ...int) {
+	drawOffsetIndex := 0
+	if len(drawOffsetIndexes) > 0 {
+		drawOffsetIndex = drawOffsetIndexes[0]
+	}
+
+	cb := canvasBox.Bottom
+	cl := canvasBox.Left
+
+	v0x, v0y1, v0y2 := bbs.GetBoundedValues(0)
+	x0 := cl + xrange.Translate(v0x)
+	y0 := cb - yrange.Translate(v0y1)
+
+	var vx, vy1, vy2 float64
+	var x, y int
+
+	xvalues := make([]float64, bbs.Len())
+	xvalues[0] = v0x
+	y2values := make([]float64, bbs.Len())
+	y2values[0] = v0y2
+
+	style.GetFillAndStrokeOptions().WriteToRenderer(r)
+	r.MoveTo(x0, y0)
+	for i := 1; i < bbs.Len(); i++ {
+		vx, vy1, vy2 = bbs.GetBoundedValues(i)
+
+		xvalues[i] = vx
+		y2values[i] = vy2
+
+		x = cl + xrange.Translate(vx)
+		y = cb - yrange.Translate(vy1)
+		if i > drawOffsetIndex {
+			r.LineTo(x, y)
+		} else {
+			r.MoveTo(x, y)
+		}
+	}
+	y = cb - yrange.Translate(vy2)
+	r.LineTo(x, y)
+	for i := bbs.Len() - 1; i >= drawOffsetIndex; i-- {
+		vx, vy2 = xvalues[i], y2values[i]
+		x = cl + xrange.Translate(vx)
+		y = cb - yrange.Translate(vy2)
+		r.LineTo(x, y)
+	}
+	r.Close()
+	r.FillStroke()
+}
+
+// HistogramSeries draws a value provider as boxes from 0.
+func (d draw) HistogramSeries(r Renderer, canvasBox Box, xrange, yrange Range, style Style, vs ValuesProvider, barWidths ...int) {
+	if vs.Len() == 0 {
+		return
+	}
+
+	//calculate bar width?
+	seriesLength := vs.Len()
+	barWidth := int(math.Floor(float64(xrange.GetDomain()) / float64(seriesLength)))
+	if len(barWidths) > 0 {
+		barWidth = barWidths[0]
+	}
+
+	cb := canvasBox.Bottom
+	cl := canvasBox.Left
+
+	//foreach datapoint, draw a box.
+	for index := 0; index < seriesLength; index++ {
+		vx, vy := vs.GetValues(index)
+		y0 := yrange.Translate(0)
+		x := cl + xrange.Translate(vx)
+		y := yrange.Translate(vy)
+
+		d.Box(r, Box{
+			Top:    cb - y0,
+			Left:   x - (barWidth >> 1),
+			Right:  x + (barWidth >> 1),
+			Bottom: cb - y,
+		}, style)
+	}
+}
+
+// MeasureAnnotation measures how big an annotation would be.
+func (d draw) MeasureAnnotation(r Renderer, canvasBox Box, style Style, lx, ly int, label string) Box {
+	style.WriteToRenderer(r)
+	defer r.ResetStyle()
+
+	textBox := r.MeasureText(label)
+	textWidth := textBox.Width()
+	textHeight := textBox.Height()
+	halfTextHeight := textHeight >> 1
+
+	pt := style.Padding.GetTop(DefaultAnnotationPadding.Top)
+	pl := style.Padding.GetLeft(DefaultAnnotationPadding.Left)
+	pr := style.Padding.GetRight(DefaultAnnotationPadding.Right)
+	pb := style.Padding.GetBottom(DefaultAnnotationPadding.Bottom)
+
+	strokeWidth := style.GetStrokeWidth()
+
+	top := ly - (pt + halfTextHeight)
+	right := lx + pl + pr + textWidth + DefaultAnnotationDeltaWidth + int(strokeWidth)
+	bottom := ly + (pb + halfTextHeight)
+
+	return Box{
+		Top:    top,
+		Left:   lx,
+		Right:  right,
+		Bottom: bottom,
+	}
+}
+
+// Annotation draws an anotation with a renderer.
+func (d draw) Annotation(r Renderer, canvasBox Box, style Style, lx, ly int, label string) {
+	style.GetTextOptions().WriteToRenderer(r)
+	defer r.ResetStyle()
+
+	textBox := r.MeasureText(label)
+	textWidth := textBox.Width()
+	halfTextHeight := textBox.Height() >> 1
+
+	style.GetFillAndStrokeOptions().WriteToRenderer(r)
+
+	pt := style.Padding.GetTop(DefaultAnnotationPadding.Top)
+	pl := style.Padding.GetLeft(DefaultAnnotationPadding.Left)
+	pr := style.Padding.GetRight(DefaultAnnotationPadding.Right)
+	pb := style.Padding.GetBottom(DefaultAnnotationPadding.Bottom)
+
+	textX := lx + pl + DefaultAnnotationDeltaWidth
+	textY := ly + halfTextHeight
+
+	ltx := lx + DefaultAnnotationDeltaWidth
+	lty := ly - (pt + halfTextHeight)
+
+	rtx := lx + pl + pr + textWidth + DefaultAnnotationDeltaWidth
+	rty := ly - (pt + halfTextHeight)
+
+	rbx := lx + pl + pr + textWidth + DefaultAnnotationDeltaWidth
+	rby := ly + (pb + halfTextHeight)
+
+	lbx := lx + DefaultAnnotationDeltaWidth
+	lby := ly + (pb + halfTextHeight)
+
+	r.MoveTo(lx, ly)
+	r.LineTo(ltx, lty)
+	r.LineTo(rtx, rty)
+	r.LineTo(rbx, rby)
+	r.LineTo(lbx, lby)
+	r.LineTo(lx, ly)
+	r.Close()
+	r.FillStroke()
+
+	style.GetTextOptions().WriteToRenderer(r)
+	r.Text(label, textX, textY)
+}
+
+// Box draws a box with a given style.
+func (d draw) Box(r Renderer, b Box, s Style) {
+	s.GetFillAndStrokeOptions().WriteToRenderer(r)
+	defer r.ResetStyle()
+
+	r.MoveTo(b.Left, b.Top)
+	r.LineTo(b.Right, b.Top)
+	r.LineTo(b.Right, b.Bottom)
+	r.LineTo(b.Left, b.Bottom)
+	r.LineTo(b.Left, b.Top)
+	r.FillStroke()
+}
+
+func (d draw) BoxRotated(r Renderer, b Box, thetaDegrees float64, s Style) {
+	d.BoxCorners(r, b.Corners().Rotate(thetaDegrees), s)
+}
+
+func (d draw) BoxCorners(r Renderer, bc BoxCorners, s Style) {
+	s.GetFillAndStrokeOptions().WriteToRenderer(r)
+	defer r.ResetStyle()
+
+	r.MoveTo(bc.TopLeft.X, bc.TopLeft.Y)
+	r.LineTo(bc.TopRight.X, bc.TopRight.Y)
+	r.LineTo(bc.BottomRight.X, bc.BottomRight.Y)
+	r.LineTo(bc.BottomLeft.X, bc.BottomLeft.Y)
+	r.Close()
+	r.FillStroke()
+}
+
+// DrawText draws text with a given style.
+func (d draw) Text(r Renderer, text string, x, y int, style Style) {
+	style.GetTextOptions().WriteToRenderer(r)
+	defer r.ResetStyle()
+
+	r.Text(text, x, y)
+}
+
+func (d draw) MeasureText(r Renderer, text string, style Style) Box {
+	style.GetTextOptions().WriteToRenderer(r)
+	defer r.ResetStyle()
+
+	return r.MeasureText(text)
+}
+
+// TextWithin draws the text within a given box.
+func (d draw) TextWithin(r Renderer, text string, box Box, style Style) {
+	style.GetTextOptions().WriteToRenderer(r)
+	defer r.ResetStyle()
+
+	lines := Text.WrapFit(r, text, box.Width(), style)
+	linesBox := Text.MeasureLines(r, lines, style)
+
+	y := box.Top
+
+	switch style.GetTextVerticalAlign() {
+	case TextVerticalAlignBottom, TextVerticalAlignBaseline: // i have to build better baseline handling into measure text
+		y = y - linesBox.Height()
+	case TextVerticalAlignMiddle:
+		y = y + (box.Height() >> 1) - (linesBox.Height() >> 1)
+	case TextVerticalAlignMiddleBaseline:
+		y = y + (box.Height() >> 1) - linesBox.Height()
+	}
+
+	var tx, ty int
+	for _, line := range lines {
+		lineBox := r.MeasureText(line)
+		switch style.GetTextHorizontalAlign() {
+		case TextHorizontalAlignCenter:
+			tx = box.Left + ((box.Width() - lineBox.Width()) >> 1)
+		case TextHorizontalAlignRight:
+			tx = box.Right - lineBox.Width()
+		default:
+			tx = box.Left
+		}
+		if style.TextRotationDegrees == 0 {
+			ty = y + lineBox.Height()
+		} else {
+			ty = y
+		}
+
+		r.Text(line, tx, ty)
+		y += lineBox.Height() + style.GetTextLineSpacing()
+	}
+}

drawing/README.md

@@ -0,0 +1,5 @@
+go-chart > drawing
+==================
+
+The bulk of the code in this package is based on [draw2d](https://github.com/llgcode/draw2d), but
+with significant modifications to make the APIs more golang friendly and careful about units (points vs. pixels).

drawing/color.go

@@ -0,0 +1,274 @@
+package drawing
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// Basic Colors from:
+// https://www.w3.org/wiki/CSS/Properties/color/keywords
+var (
+	// ColorTransparent is a fully transparent color.
+	ColorTransparent = Color{R: 255, G: 255, B: 255, A: 0}
+	// ColorWhite is white.
+	ColorWhite = Color{R: 255, G: 255, B: 255, A: 255}
+	// ColorBlack is black.
+	ColorBlack = Color{R: 0, G: 0, B: 0, A: 255}
+	// ColorRed is red.
+	ColorRed = Color{R: 255, G: 0, B: 0, A: 255}
+	// ColorGreen is green.
+	ColorGreen = Color{R: 0, G: 128, B: 0, A: 255}
+	// ColorBlue is blue.
+	ColorBlue = Color{R: 0, G: 0, B: 255, A: 255}
+	// ColorSilver is a known color.
+	ColorSilver = Color{R: 192, G: 192, B: 192, A: 255}
+	// ColorMaroon is a known color.
+	ColorMaroon = Color{R: 128, G: 0, B: 0, A: 255}
+	// ColorPurple is a known color.
+	ColorPurple = Color{R: 128, G: 0, B: 128, A: 255}
+	// ColorFuchsia is a known color.
+	ColorFuchsia = Color{R: 255, G: 0, B: 255, A: 255}
+	// ColorLime is a known color.
+	ColorLime = Color{R: 0, G: 255, B: 0, A: 255}
+	// ColorOlive is a known color.
+	ColorOlive = Color{R: 128, G: 128, B: 0, A: 255}
+	// ColorYellow is a known color.
+	ColorYellow = Color{R: 255, G: 255, B: 0, A: 255}
+	// ColorNavy is a known color.
+	ColorNavy = Color{R: 0, G: 0, B: 128, A: 255}
+	// ColorTeal is a known color.
+	ColorTeal = Color{R: 0, G: 128, B: 128, A: 255}
+	// ColorAqua is a known color.
+	ColorAqua = Color{R: 0, G: 255, B: 255, A: 255}
+)
+
+func parseHex(hex string) uint8 {
+	v, _ := strconv.ParseInt(hex, 16, 16)
+	return uint8(v)
+}
+
+// ParseColor parses a color from a string.
+func ParseColor(rawColor string) Color {
+	if strings.HasPrefix(rawColor, "rgba") {
+		return ColorFromRGBA(rawColor)
+	}
+	if strings.HasPrefix(rawColor, "rgb") {
+		return ColorFromRGB(rawColor)
+	}
+	if strings.HasPrefix(rawColor, "#") {
+		return ColorFromHex(rawColor)
+	}
+	return ColorFromKnown(rawColor)
+}
+
+var rgbaexpr = regexp.MustCompile(`rgba\((?P<R>.+),(?P<G>.+),(?P<B>.+),(?P<A>.+)\)`)
+
+// ColorFromRGBA returns a color from an `rgba()` css function.
+func ColorFromRGBA(rgba string) (output Color) {
+	values := rgbaexpr.FindStringSubmatch(rgba)
+	for i, name := range rgbaexpr.SubexpNames() {
+		if i == 0 {
+			continue
+		}
+		if i >= len(values) {
+			break
+		}
+		switch name {
+		case "R":
+			value := strings.TrimSpace(values[i])
+			parsed, _ := strconv.ParseInt(value, 10, 16)
+			output.R = uint8(parsed)
+		case "G":
+			value := strings.TrimSpace(values[i])
+			parsed, _ := strconv.ParseInt(value, 10, 16)
+			output.G = uint8(parsed)
+		case "B":
+			value := strings.TrimSpace(values[i])
+			parsed, _ := strconv.ParseInt(value, 10, 16)
+			output.B = uint8(parsed)
+		case "A":
+			value := strings.TrimSpace(values[i])
+			parsed, _ := strconv.ParseFloat(value, 32)
+			if parsed > 1 {
+				parsed = 1
+			} else if parsed < 0 {
+				parsed = 0
+			}
+			output.A = uint8(parsed * 255)
+		}
+	}
+	return
+}
+
+var rgbexpr = regexp.MustCompile(`rgb\((?P<R>.+),(?P<G>.+),(?P<B>.+)\)`)
+
+// ColorFromRGB returns a color from an `rgb()` css function.
+func ColorFromRGB(rgb string) (output Color) {
+	output.A = 255
+	values := rgbexpr.FindStringSubmatch(rgb)
+	for i, name := range rgbaexpr.SubexpNames() {
+		if i == 0 {
+			continue
+		}
+		if i >= len(values) {
+			break
+		}
+		switch name {
+		case "R":
+			value := strings.TrimSpace(values[i])
+			parsed, _ := strconv.ParseInt(value, 10, 16)
+			output.R = uint8(parsed)
+		case "G":
+			value := strings.TrimSpace(values[i])
+			parsed, _ := strconv.ParseInt(value, 10, 16)
+			output.G = uint8(parsed)
+		case "B":
+			value := strings.TrimSpace(values[i])
+			parsed, _ := strconv.ParseInt(value, 10, 16)
+			output.B = uint8(parsed)
+		}
+	}
+	return
+}
+
+// ColorFromHex returns a color from a css hex code.
+//
+// NOTE: it will trim a leading '#' character if present.
+func ColorFromHex(hex string) Color {
+	if strings.HasPrefix(hex, "#") {
+		hex = strings.TrimPrefix(hex, "#")
+	}
+	var c Color
+	if len(hex) == 3 {
+		c.R = parseHex(string(hex[0])) * 0x11
+		c.G = parseHex(string(hex[1])) * 0x11
+		c.B = parseHex(string(hex[2])) * 0x11
+	} else {
+		c.R = parseHex(string(hex[0:2]))
+		c.G = parseHex(string(hex[2:4]))
+		c.B = parseHex(string(hex[4:6]))
+	}
+	c.A = 255
+	return c
+}
+
+// ColorFromKnown returns an internal color from a known (basic) color name.
+func ColorFromKnown(known string) Color {
+	switch strings.ToLower(known) {
+	case "transparent":
+		return ColorTransparent
+	case "white":
+		return ColorWhite
+	case "black":
+		return ColorBlack
+	case "red":
+		return ColorRed
+	case "blue":
+		return ColorBlue
+	case "green":
+		return ColorGreen
+	case "silver":
+		return ColorSilver
+	case "maroon":
+		return ColorMaroon
+	case "purple":
+		return ColorPurple
+	case "fuchsia":
+		return ColorFuchsia
+	case "lime":
+		return ColorLime
+	case "olive":
+		return ColorOlive
+	case "yellow":
+		return ColorYellow
+	case "navy":
+		return ColorNavy
+	case "teal":
+		return ColorTeal
+	case "aqua":
+		return ColorAqua
+	default:
+		return Color{}
+	}
+}
+
+// ColorFromAlphaMixedRGBA returns the system alpha mixed rgba values.
+func ColorFromAlphaMixedRGBA(r, g, b, a uint32) Color {
+	fa := float64(a) / 255.0
+	var c Color
+	c.R = uint8(float64(r) / fa)
+	c.G = uint8(float64(g) / fa)
+	c.B = uint8(float64(b) / fa)
+	c.A = uint8(a | (a >> 8))
+	return c
+}
+
+// ColorChannelFromFloat returns a normalized byte from a given float value.
+func ColorChannelFromFloat(v float64) uint8 {
+	return uint8(v * 255)
+}
+
+// Color is our internal color type because color.Color is bullshit.
+type Color struct {
+	R, G, B, A uint8
+}
+
+// RGBA returns the color as a pre-alpha mixed color set.
+func (c Color) RGBA() (r, g, b, a uint32) {
+	fa := float64(c.A) / 255.0
+	r = uint32(float64(uint32(c.R)) * fa)
+	r |= r << 8
+	g = uint32(float64(uint32(c.G)) * fa)
+	g |= g << 8
+	b = uint32(float64(uint32(c.B)) * fa)
+	b |= b << 8
+	a = uint32(c.A)
+	a |= a << 8
+	return
+}
+
+// IsZero returns if the color has been set or not.
+func (c Color) IsZero() bool {
+	return c.R == 0 && c.G == 0 && c.B == 0 && c.A == 0
+}
+
+// IsTransparent returns if the colors alpha channel is zero.
+func (c Color) IsTransparent() bool {
+	return c.A == 0
+}
+
+// WithAlpha returns a copy of the color with a given alpha.
+func (c Color) WithAlpha(a uint8) Color {
+	return Color{
+		R: c.R,
+		G: c.G,
+		B: c.B,
+		A: a,
+	}
+}
+
+// Equals returns true if the color equals another.
+func (c Color) Equals(other Color) bool {
+	return c.R == other.R &&
+		c.G == other.G &&
+		c.B == other.B &&
+		c.A == other.A
+}
+
+// AverageWith averages two colors.
+func (c Color) AverageWith(other Color) Color {
+	return Color{
+		R: (c.R + other.R) >> 1,
+		G: (c.G + other.G) >> 1,
+		B: (c.B + other.B) >> 1,
+		A: c.A,
+	}
+}
+
+// String returns a css string representation of the color.
+func (c Color) String() string {
+	fa := float64(c.A) / float64(255)
+	return fmt.Sprintf("rgba(%v,%v,%v,%.1f)", c.R, c.G, c.B, fa)
+}

drawing/color_test.go

@@ -0,0 +1,114 @@
+package drawing
+
+import (
+	"fmt"
+	"testing"
+
+	"image/color"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestColorFromHex(t *testing.T) {
+	white := ColorFromHex("FFFFFF")
+	testutil.AssertEqual(t, ColorWhite, white)
+
+	shortWhite := ColorFromHex("FFF")
+	testutil.AssertEqual(t, ColorWhite, shortWhite)
+
+	black := ColorFromHex("000000")
+	testutil.AssertEqual(t, ColorBlack, black)
+
+	shortBlack := ColorFromHex("000")
+	testutil.AssertEqual(t, ColorBlack, shortBlack)
+
+	red := ColorFromHex("FF0000")
+	testutil.AssertEqual(t, ColorRed, red)
+
+	shortRed := ColorFromHex("F00")
+	testutil.AssertEqual(t, ColorRed, shortRed)
+
+	green := ColorFromHex("008000")
+	testutil.AssertEqual(t, ColorGreen, green)
+
+	// shortGreen := ColorFromHex("0F0")
+	// testutil.AssertEqual(t, ColorGreen, shortGreen)
+
+	blue := ColorFromHex("0000FF")
+	testutil.AssertEqual(t, ColorBlue, blue)
+
+	shortBlue := ColorFromHex("00F")
+	testutil.AssertEqual(t, ColorBlue, shortBlue)
+}
+
+func TestColorFromHex_handlesHash(t *testing.T) {
+	withHash := ColorFromHex("#FF0000")
+	testutil.AssertEqual(t, ColorRed, withHash)
+
+	withoutHash := ColorFromHex("#FF0000")
+	testutil.AssertEqual(t, ColorRed, withoutHash)
+}
+
+func TestColorFromAlphaMixedRGBA(t *testing.T) {
+	black := ColorFromAlphaMixedRGBA(color.Black.RGBA())
+	testutil.AssertTrue(t, black.Equals(ColorBlack), black.String())
+
+	white := ColorFromAlphaMixedRGBA(color.White.RGBA())
+	testutil.AssertTrue(t, white.Equals(ColorWhite), white.String())
+}
+
+func Test_ColorFromRGBA(t *testing.T) {
+	value := "rgba(192, 192, 192, 1.0)"
+	parsed := ColorFromRGBA(value)
+	testutil.AssertEqual(t, ColorSilver, parsed)
+
+	value = "rgba(192,192,192,1.0)"
+	parsed = ColorFromRGBA(value)
+	testutil.AssertEqual(t, ColorSilver, parsed)
+
+	value = "rgba(192,192,192,1.5)"
+	parsed = ColorFromRGBA(value)
+	testutil.AssertEqual(t, ColorSilver, parsed)
+}
+
+func TestParseColor(t *testing.T) {
+	testCases := [...]struct {
+		Input    string
+		Expected Color
+	}{
+		{"", Color{}},
+		{"white", ColorWhite},
+		{"WHITE", ColorWhite}, // caps!
+		{"black", ColorBlack},
+		{"red", ColorRed},
+		{"green", ColorGreen},
+		{"blue", ColorBlue},
+		{"silver", ColorSilver},
+		{"maroon", ColorMaroon},
+		{"purple", ColorPurple},
+		{"fuchsia", ColorFuchsia},
+		{"lime", ColorLime},
+		{"olive", ColorOlive},
+		{"yellow", ColorYellow},
+		{"navy", ColorNavy},
+		{"teal", ColorTeal},
+		{"aqua", ColorAqua},
+
+		{"rgba(192, 192, 192, 1.0)", ColorSilver},
+		{"rgba(192,192,192,1.0)", ColorSilver},
+		{"rgb(192, 192, 192)", ColorSilver},
+		{"rgb(192,192,192)", ColorSilver},
+
+		{"#FF0000", ColorRed},
+		{"#008000", ColorGreen},
+		{"#0000FF", ColorBlue},
+		{"#F00", ColorRed},
+		{"#080", Color{0, 136, 0, 255}},
+		{"#00F", ColorBlue},
+	}
+
+	for index, tc := range testCases {
+		actual := ParseColor(tc.Input)
+		testutil.AssertEqual(t, tc.Expected, actual, fmt.Sprintf("test case: %d -> %s", index, tc.Input))
+	}
+}

drawing/constants.go

@@ -0,0 +1,6 @@
+package drawing
+
+const (
+	// DefaultDPI is the default image DPI.
+	DefaultDPI = 96.0
+)

drawing/curve.go

@@ -0,0 +1,185 @@
+package drawing
+
+import "math"
+
+const (
+	// CurveRecursionLimit represents the maximum recursion that is really necessary to subsivide a curve into straight lines
+	CurveRecursionLimit = 32
+)
+
+// Cubic
+//	x1, y1, cpx1, cpy1, cpx2, cpy2, x2, y2 float64
+
+// SubdivideCubic a Bezier cubic curve in 2 equivalents Bezier cubic curves.
+// c1 and c2 parameters are the resulting curves
+func SubdivideCubic(c, c1, c2 []float64) {
+	// First point of c is the first point of c1
+	c1[0], c1[1] = c[0], c[1]
+	// Last point of c is the last point of c2
+	c2[6], c2[7] = c[6], c[7]
+
+	// Subdivide segment using midpoints
+	c1[2] = (c[0] + c[2]) / 2
+	c1[3] = (c[1] + c[3]) / 2
+
+	midX := (c[2] + c[4]) / 2
+	midY := (c[3] + c[5]) / 2
+
+	c2[4] = (c[4] + c[6]) / 2
+	c2[5] = (c[5] + c[7]) / 2
+
+	c1[4] = (c1[2] + midX) / 2
+	c1[5] = (c1[3] + midY) / 2
+
+	c2[2] = (midX + c2[4]) / 2
+	c2[3] = (midY + c2[5]) / 2
+
+	c1[6] = (c1[4] + c2[2]) / 2
+	c1[7] = (c1[5] + c2[3]) / 2
+
+	// Last Point of c1 is equal to the first point of c2
+	c2[0], c2[1] = c1[6], c1[7]
+}
+
+// TraceCubic generate lines subdividing the cubic curve using a Liner
+// flattening_threshold helps determines the flattening expectation of the curve
+func TraceCubic(t Liner, cubic []float64, flatteningThreshold float64) {
+	// Allocation curves
+	var curves [CurveRecursionLimit * 8]float64
+	copy(curves[0:8], cubic[0:8])
+	i := 0
+
+	// current curve
+	var c []float64
+
+	var dx, dy, d2, d3 float64
+
+	for i >= 0 {
+		c = curves[i*8:]
+		dx = c[6] - c[0]
+		dy = c[7] - c[1]
+
+		d2 = math.Abs((c[2]-c[6])*dy - (c[3]-c[7])*dx)
+		d3 = math.Abs((c[4]-c[6])*dy - (c[5]-c[7])*dx)
+
+		// if it's flat then trace a line
+		if (d2+d3)*(d2+d3) < flatteningThreshold*(dx*dx+dy*dy) || i == len(curves)-1 {
+			t.LineTo(c[6], c[7])
+			i--
+		} else {
+			// second half of bezier go lower onto the stack
+			SubdivideCubic(c, curves[(i+1)*8:], curves[i*8:])
+			i++
+		}
+	}
+}
+
+// Quad
+// x1, y1, cpx1, cpy2, x2, y2 float64
+
+// SubdivideQuad a Bezier quad curve in 2 equivalents Bezier quad curves.
+// c1 and c2 parameters are the resulting curves
+func SubdivideQuad(c, c1, c2 []float64) {
+	// First point of c is the first point of c1
+	c1[0], c1[1] = c[0], c[1]
+	// Last point of c is the last point of c2
+	c2[4], c2[5] = c[4], c[5]
+
+	// Subdivide segment using midpoints
+	c1[2] = (c[0] + c[2]) / 2
+	c1[3] = (c[1] + c[3]) / 2
+	c2[2] = (c[2] + c[4]) / 2
+	c2[3] = (c[3] + c[5]) / 2
+	c1[4] = (c1[2] + c2[2]) / 2
+	c1[5] = (c1[3] + c2[3]) / 2
+	c2[0], c2[1] = c1[4], c1[5]
+	return
+}
+
+func traceWindowIndices(i int) (startAt, endAt int) {
+	startAt = i * 6
+	endAt = startAt + 6
+	return
+}
+
+func traceCalcDeltas(c []float64) (dx, dy, d float64) {
+	dx = c[4] - c[0]
+	dy = c[5] - c[1]
+	d = math.Abs(((c[2]-c[4])*dy - (c[3]-c[5])*dx))
+	return
+}
+
+func traceIsFlat(dx, dy, d, threshold float64) bool {
+	return (d * d) < threshold*(dx*dx+dy*dy)
+}
+
+func traceGetWindow(curves []float64, i int) []float64 {
+	startAt, endAt := traceWindowIndices(i)
+	return curves[startAt:endAt]
+}
+
+// TraceQuad generate lines subdividing the curve using a Liner
+// flattening_threshold helps determines the flattening expectation of the curve
+func TraceQuad(t Liner, quad []float64, flatteningThreshold float64) {
+	const curveLen = CurveRecursionLimit * 6
+	const curveEndIndex = curveLen - 1
+	const lastIteration = CurveRecursionLimit - 1
+
+	// Allocates curves stack
+	curves := make([]float64, curveLen)
+
+	// copy 6 elements from the quad path to the stack
+	copy(curves[0:6], quad[0:6])
+
+	var i int
+	var c []float64
+	var dx, dy, d float64
+
+	for i >= 0 {
+		c = traceGetWindow(curves, i)
+		dx, dy, d = traceCalcDeltas(c)
+
+		// bail early if the distance is 0
+		if d == 0 {
+			return
+		}
+
+		// if it's flat then trace a line
+		if traceIsFlat(dx, dy, d, flatteningThreshold) || i == lastIteration {
+			t.LineTo(c[4], c[5])
+			i--
+		} else {
+			SubdivideQuad(c, traceGetWindow(curves, i+1), traceGetWindow(curves, i))
+			i++
+		}
+	}
+}
+
+// TraceArc trace an arc using a Liner
+func TraceArc(t Liner, x, y, rx, ry, start, angle, scale float64) (lastX, lastY float64) {
+	end := start + angle
+	clockWise := true
+	if angle < 0 {
+		clockWise = false
+	}
+	ra := (math.Abs(rx) + math.Abs(ry)) / 2
+	da := math.Acos(ra/(ra+0.125/scale)) * 2
+	//normalize
+	if !clockWise {
+		da = -da
+	}
+	angle = start + da
+	var curX, curY float64
+	for {
+		if (angle < end-da/4) != clockWise {
+			curX = x + math.Cos(end)*rx
+			curY = y + math.Sin(end)*ry
+			return curX, curY
+		}
+		curX = x + math.Cos(angle)*rx
+		curY = y + math.Sin(angle)*ry
+
+		angle += da
+		t.LineTo(curX, curY)
+	}
+}

drawing/curve_test.go

@@ -0,0 +1,35 @@
+package drawing
+
+import (
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+type point struct {
+	X, Y float64
+}
+
+type mockLine struct {
+	inner []point
+}
+
+func (ml *mockLine) LineTo(x, y float64) {
+	ml.inner = append(ml.inner, point{x, y})
+}
+
+func (ml mockLine) Len() int {
+	return len(ml.inner)
+}
+
+func TestTraceQuad(t *testing.T) {
+	// replaced new assertions helper
+
+	// Quad
+	// x1, y1, cpx1, cpy2, x2, y2 float64
+	// do the 9->12 circle segment
+	quad := []float64{10, 20, 20, 20, 20, 10}
+	liner := &mockLine{}
+	TraceQuad(liner, quad, 0.5)
+	testutil.AssertNotZero(t, liner.Len())
+}

drawing/dasher.go

@@ -0,0 +1,89 @@
+package drawing
+
+// NewDashVertexConverter creates a new dash converter.
+func NewDashVertexConverter(dash []float64, dashOffset float64, flattener Flattener) *DashVertexConverter {
+	var dasher DashVertexConverter
+	dasher.dash = dash
+	dasher.currentDash = 0
+	dasher.dashOffset = dashOffset
+	dasher.next = flattener
+	return &dasher
+}
+
+// DashVertexConverter is a converter for dash vertexes.
+type DashVertexConverter struct {
+	next           Flattener
+	x, y, distance float64
+	dash           []float64
+	currentDash    int
+	dashOffset     float64
+}
+
+// LineTo implements the pathbuilder interface.
+func (dasher *DashVertexConverter) LineTo(x, y float64) {
+	dasher.lineTo(x, y)
+}
+
+// MoveTo implements the pathbuilder interface.
+func (dasher *DashVertexConverter) MoveTo(x, y float64) {
+	dasher.next.MoveTo(x, y)
+	dasher.x, dasher.y = x, y
+	dasher.distance = dasher.dashOffset
+	dasher.currentDash = 0
+}
+
+// LineJoin implements the pathbuilder interface.
+func (dasher *DashVertexConverter) LineJoin() {
+	dasher.next.LineJoin()
+}
+
+// Close implements the pathbuilder interface.
+func (dasher *DashVertexConverter) Close() {
+	dasher.next.Close()
+}
+
+// End implements the pathbuilder interface.
+func (dasher *DashVertexConverter) End() {
+	dasher.next.End()
+}
+
+func (dasher *DashVertexConverter) lineTo(x, y float64) {
+	rest := dasher.dash[dasher.currentDash] - dasher.distance
+	for rest < 0 {
+		dasher.distance = dasher.distance - dasher.dash[dasher.currentDash]
+		dasher.currentDash = (dasher.currentDash + 1) % len(dasher.dash)
+		rest = dasher.dash[dasher.currentDash] - dasher.distance
+	}
+	d := distance(dasher.x, dasher.y, x, y)
+	for d >= rest {
+		k := rest / d
+		lx := dasher.x + k*(x-dasher.x)
+		ly := dasher.y + k*(y-dasher.y)
+		if dasher.currentDash%2 == 0 {
+			// line
+			dasher.next.LineTo(lx, ly)
+		} else {
+			// gap
+			dasher.next.End()
+			dasher.next.MoveTo(lx, ly)
+		}
+		d = d - rest
+		dasher.x, dasher.y = lx, ly
+		dasher.currentDash = (dasher.currentDash + 1) % len(dasher.dash)
+		rest = dasher.dash[dasher.currentDash]
+	}
+	dasher.distance = d
+	if dasher.currentDash%2 == 0 {
+		// line
+		dasher.next.LineTo(x, y)
+	} else {
+		// gap
+		dasher.next.End()
+		dasher.next.MoveTo(x, y)
+	}
+	if dasher.distance >= dasher.dash[dasher.currentDash] {
+		dasher.distance = dasher.distance - dasher.dash[dasher.currentDash]
+		dasher.currentDash = (dasher.currentDash + 1) % len(dasher.dash)
+	}
+	dasher.x, dasher.y = x, y
+}

drawing/demux_flattener.go

@@ -0,0 +1,41 @@
+package drawing
+
+// DemuxFlattener is a flattener
+type DemuxFlattener struct {
+	Flatteners []Flattener
+}
+
+// MoveTo implements the path builder interface.
+func (dc DemuxFlattener) MoveTo(x, y float64) {
+	for _, flattener := range dc.Flatteners {
+		flattener.MoveTo(x, y)
+	}
+}
+
+// LineTo implements the path builder interface.
+func (dc DemuxFlattener) LineTo(x, y float64) {
+	for _, flattener := range dc.Flatteners {
+		flattener.LineTo(x, y)
+	}
+}
+
+// LineJoin implements the path builder interface.
+func (dc DemuxFlattener) LineJoin() {
+	for _, flattener := range dc.Flatteners {
+		flattener.LineJoin()
+	}
+}
+
+// Close implements the path builder interface.
+func (dc DemuxFlattener) Close() {
+	for _, flattener := range dc.Flatteners {
+		flattener.Close()
+	}
+}
+
+// End implements the path builder interface.
+func (dc DemuxFlattener) End() {
+	for _, flattener := range dc.Flatteners {
+		flattener.End()
+	}
+}

drawing/drawing.go

@@ -0,0 +1,148 @@
+package drawing
+
+import (
+	"image/color"
+
+	"github.com/golang/freetype/truetype"
+)
+
+// FillRule defines the type for fill rules
+type FillRule int
+
+const (
+	// FillRuleEvenOdd determines the "insideness" of a point in the shape
+	// by drawing a ray from that point to infinity in any direction
+	// and counting the number of path segments from the given shape that the ray crosses.
+	// If this number is odd, the point is inside; if even, the point is outside.
+	FillRuleEvenOdd FillRule = iota
+	// FillRuleWinding determines the "insideness" of a point in the shape
+	// by drawing a ray from that point to infinity in any direction
+	// and then examining the places where a segment of the shape crosses the ray.
+	// Starting with a count of zero, add one each time a path segment crosses
+	// the ray from left to right and subtract one each time
+	// a path segment crosses the ray from right to left. After counting the crossings,
+	// if the result is zero then the point is outside the path. Otherwise, it is inside.
+	FillRuleWinding
+)
+
+// LineCap is the style of line extremities
+type LineCap int
+
+const (
+	// RoundCap defines a rounded shape at the end of the line
+	RoundCap LineCap = iota
+	// ButtCap defines a squared shape exactly at the end of the line
+	ButtCap
+	// SquareCap defines a squared shape at the end of the line
+	SquareCap
+)
+
+// LineJoin is the style of segments joint
+type LineJoin int
+
+const (
+	// BevelJoin represents cut segments joint
+	BevelJoin LineJoin = iota
+	// RoundJoin represents rounded segments joint
+	RoundJoin
+	// MiterJoin represents peaker segments joint
+	MiterJoin
+)
+
+// StrokeStyle keeps stroke style attributes
+// that is used by the Stroke method of a Drawer
+type StrokeStyle struct {
+	// Color defines the color of stroke
+	Color color.Color
+	// Line width
+	Width float64
+	// Line cap style rounded, butt or square
+	LineCap LineCap
+	// Line join style bevel, round or miter
+	LineJoin LineJoin
+	// offset of the first dash
+	DashOffset float64
+	// array represented dash length pair values are plain dash and impair are space between dash
+	// if empty display plain line
+	Dash []float64
+}
+
+// SolidFillStyle define style attributes for a solid fill style
+type SolidFillStyle struct {
+	// Color defines the line color
+	Color color.Color
+	// FillRule defines the file rule to used
+	FillRule FillRule
+}
+
+// Valign Vertical Alignment of the text
+type Valign int
+
+const (
+	// ValignTop top align text
+	ValignTop Valign = iota
+	// ValignCenter centered text
+	ValignCenter
+	// ValignBottom bottom aligned text
+	ValignBottom
+	// ValignBaseline align text with the baseline of the font
+	ValignBaseline
+)
+
+// Halign Horizontal Alignment of the text
+type Halign int
+
+const (
+	// HalignLeft Horizontally align to left
+	HalignLeft = iota
+	// HalignCenter Horizontally align to center
+	HalignCenter
+	// HalignRight Horizontally align to right
+	HalignRight
+)
+
+// TextStyle describe text property
+type TextStyle struct {
+	// Color defines the color of text
+	Color color.Color
+	// Size font size
+	Size float64
+	// The font to use
+	Font *truetype.Font
+	// Horizontal Alignment of the text
+	Halign Halign
+	// Vertical Alignment of the text
+	Valign Valign
+}
+
+// ScalingPolicy is a constant to define how to scale an image
+type ScalingPolicy int
+
+const (
+	// ScalingNone no scaling applied
+	ScalingNone ScalingPolicy = iota
+	// ScalingStretch the image is stretched so that its width and height are exactly the given width and height
+	ScalingStretch
+	// ScalingWidth the image is scaled so that its width is exactly the given width
+	ScalingWidth
+	// ScalingHeight the image is scaled so that its height is exactly the given height
+	ScalingHeight
+	// ScalingFit the image is scaled to the largest scale that allow the image to fit within a rectangle width x height
+	ScalingFit
+	// ScalingSameArea the image is scaled so that its area is exactly the area of the given rectangle width x height
+	ScalingSameArea
+	// ScalingFill the image is scaled to the smallest scale that allow the image to fully cover a rectangle width x height
+	ScalingFill
+)
+
+// ImageScaling style attributes used to display the image
+type ImageScaling struct {
+	// Horizontal Alignment of the image
+	Halign Halign
+	// Vertical Alignment of the image
+	Valign Valign
+	// Width Height used by scaling policy
+	Width, Height float64
+	// ScalingPolicy defines the scaling policy to applied to the image
+	ScalingPolicy ScalingPolicy
+}

drawing/flattener.go

@@ -0,0 +1,97 @@
+package drawing
+
+// Liner receive segment definition
+type Liner interface {
+	// LineTo Draw a line from the current position to the point (x, y)
+	LineTo(x, y float64)
+}
+
+// Flattener receive segment definition
+type Flattener interface {
+	// MoveTo Start a New line from the point (x, y)
+	MoveTo(x, y float64)
+	// LineTo Draw a line from the current position to the point (x, y)
+	LineTo(x, y float64)
+	// LineJoin add the most recent starting point to close the path to create a polygon
+	LineJoin()
+	// Close add the most recent starting point to close the path to create a polygon
+	Close()
+	// End mark the current line as finished so we can draw caps
+	End()
+}
+
+// Flatten convert curves into straight segments keeping join segments info
+func Flatten(path *Path, flattener Flattener, scale float64) {
+	// First Point
+	var startX, startY float64
+	// Current Point
+	var x, y float64
+	var i int
+	for _, cmp := range path.Components {
+		switch cmp {
+		case MoveToComponent:
+			x, y = path.Points[i], path.Points[i+1]
+			startX, startY = x, y
+			if i != 0 {
+				flattener.End()
+			}
+			flattener.MoveTo(x, y)
+			i += 2
+		case LineToComponent:
+			x, y = path.Points[i], path.Points[i+1]
+			flattener.LineTo(x, y)
+			flattener.LineJoin()
+			i += 2
+		case QuadCurveToComponent:
+			// we include the previous point for the start of the curve
+			TraceQuad(flattener, path.Points[i-2:], 0.5)
+			x, y = path.Points[i+2], path.Points[i+3]
+			flattener.LineTo(x, y)
+			i += 4
+		case CubicCurveToComponent:
+			TraceCubic(flattener, path.Points[i-2:], 0.5)
+			x, y = path.Points[i+4], path.Points[i+5]
+			flattener.LineTo(x, y)
+			i += 6
+		case ArcToComponent:
+			x, y = TraceArc(flattener, path.Points[i], path.Points[i+1], path.Points[i+2], path.Points[i+3], path.Points[i+4], path.Points[i+5], scale)
+			flattener.LineTo(x, y)
+			i += 6
+		case CloseComponent:
+			flattener.LineTo(startX, startY)
+			flattener.Close()
+		}
+	}
+	flattener.End()
+}
+
+// SegmentedPath is a path of disparate point sectinos.
+type SegmentedPath struct {
+	Points []float64
+}
+
+// MoveTo implements the path interface.
+func (p *SegmentedPath) MoveTo(x, y float64) {
+	p.Points = append(p.Points, x, y)
+	// TODO need to mark this point as moveto
+}
+
+// LineTo implements the path interface.
+func (p *SegmentedPath) LineTo(x, y float64) {
+	p.Points = append(p.Points, x, y)
+}
+
+// LineJoin implements the path interface.
+func (p *SegmentedPath) LineJoin() {
+	// TODO need to mark the current point as linejoin
+}
+
+// Close implements the path interface.
+func (p *SegmentedPath) Close() {
+	// TODO Close
+}
+
+// End implements the path interface.
+func (p *SegmentedPath) End() {
+	// Nothing to do
+}

drawing/free_type_path.go

@@ -0,0 +1,30 @@
+package drawing
+
+import (
+	"github.com/golang/freetype/raster"
+	"golang.org/x/image/math/fixed"
+)
+
+// FtLineBuilder is a builder for freetype raster glyphs.
+type FtLineBuilder struct {
+	Adder raster.Adder
+}
+
+// MoveTo implements the path builder interface.
+func (liner FtLineBuilder) MoveTo(x, y float64) {
+	liner.Adder.Start(fixed.Point26_6{X: fixed.Int26_6(x * 64), Y: fixed.Int26_6(y * 64)})
+}
+
+// LineTo implements the path builder interface.
+func (liner FtLineBuilder) LineTo(x, y float64) {
+	liner.Adder.Add1(fixed.Point26_6{X: fixed.Int26_6(x * 64), Y: fixed.Int26_6(y * 64)})
+}
+
+// LineJoin implements the path builder interface.
+func (liner FtLineBuilder) LineJoin() {}
+
+// Close implements the path builder interface.
+func (liner FtLineBuilder) Close() {}
+
+// End implements the path builder interface.
+func (liner FtLineBuilder) End() {}

drawing/graphic_context.go

@@ -0,0 +1,82 @@
+package drawing
+
+import (
+	"image"
+	"image/color"
+
+	"github.com/golang/freetype/truetype"
+)
+
+// GraphicContext describes the interface for the various backends (images, pdf, opengl, ...)
+type GraphicContext interface {
+	// PathBuilder describes the interface for path drawing
+	PathBuilder
+	// BeginPath creates a new path
+	BeginPath()
+	// GetMatrixTransform returns the current transformation matrix
+	GetMatrixTransform() Matrix
+	// SetMatrixTransform sets the current transformation matrix
+	SetMatrixTransform(tr Matrix)
+	// ComposeMatrixTransform composes the current transformation matrix with tr
+	ComposeMatrixTransform(tr Matrix)
+	// Rotate applies a rotation to the current transformation matrix. angle is in radian.
+	Rotate(angle float64)
+	// Translate applies a translation to the current transformation matrix.
+	Translate(tx, ty float64)
+	// Scale applies a scale to the current transformation matrix.
+	Scale(sx, sy float64)
+	// SetStrokeColor sets the current stroke color
+	SetStrokeColor(c color.Color)
+	// SetFillColor sets the current fill color
+	SetFillColor(c color.Color)
+	// SetFillRule sets the current fill rule
+	SetFillRule(f FillRule)
+	// SetLineWidth sets the current line width
+	SetLineWidth(lineWidth float64)
+	// SetLineCap sets the current line cap
+	SetLineCap(cap LineCap)
+	// SetLineJoin sets the current line join
+	SetLineJoin(join LineJoin)
+	// SetLineDash sets the current dash
+	SetLineDash(dash []float64, dashOffset float64)
+	// SetFontSize sets the current font size
+	SetFontSize(fontSize float64)
+	// GetFontSize gets the current font size
+	GetFontSize() float64
+	// SetFont sets the font for the context
+	SetFont(f *truetype.Font)
+	// GetFont returns the current font
+	GetFont() *truetype.Font
+	// DrawImage draws the raster image in the current canvas
+	DrawImage(image image.Image)
+	// Save the context and push it to the context stack
+	Save()
+	// Restore remove the current context and restore the last one
+	Restore()
+	// Clear fills the current canvas with a default transparent color
+	Clear()
+	// ClearRect fills the specified rectangle with a default transparent color
+	ClearRect(x1, y1, x2, y2 int)
+	// SetDPI sets the current DPI
+	SetDPI(dpi int)
+	// GetDPI gets the current DPI
+	GetDPI() int
+	// GetStringBounds gets pixel bounds(dimensions) of given string
+	GetStringBounds(s string) (left, top, right, bottom float64)
+	// CreateStringPath creates a path from the string s at x, y
+	CreateStringPath(text string, x, y float64) (cursor float64)
+	// FillString draws the text at point (0, 0)
+	FillString(text string) (cursor float64)
+	// FillStringAt draws the text at the specified point (x, y)
+	FillStringAt(text string, x, y float64) (cursor float64)
+	// StrokeString draws the contour of the text at point (0, 0)
+	StrokeString(text string) (cursor float64)
+	// StrokeStringAt draws the contour of the text at point (x, y)
+	StrokeStringAt(text string, x, y float64) (cursor float64)
+	// Stroke strokes the paths with the color specified by SetStrokeColor
+	Stroke(paths ...*Path)
+	// Fill fills the paths with the color specified by SetFillColor
+	Fill(paths ...*Path)
+	// FillStroke first fills the paths and than strokes them
+	FillStroke(paths ...*Path)
+}

drawing/image_filter.go

@@ -0,0 +1,13 @@
+package drawing
+
+// ImageFilter defines the type of filter to use
+type ImageFilter int
+
+const (
+	// LinearFilter defines a linear filter
+	LinearFilter ImageFilter = iota
+	// BilinearFilter defines a bilinear filter
+	BilinearFilter
+	// BicubicFilter defines a bicubic filter
+	BicubicFilter
+)

drawing/line.go

@@ -0,0 +1,48 @@
+package drawing
+
+import (
+	"image/color"
+	"image/draw"
+)
+
+// PolylineBresenham draws a polyline to an image
+func PolylineBresenham(img draw.Image, c color.Color, s ...float64) {
+	for i := 2; i < len(s); i += 2 {
+		Bresenham(img, c, int(s[i-2]+0.5), int(s[i-1]+0.5), int(s[i]+0.5), int(s[i+1]+0.5))
+	}
+}
+
+// Bresenham draws a line between (x0, y0) and (x1, y1)
+func Bresenham(img draw.Image, color color.Color, x0, y0, x1, y1 int) {
+	dx := abs(x1 - x0)
+	dy := abs(y1 - y0)
+	var sx, sy int
+	if x0 < x1 {
+		sx = 1
+	} else {
+		sx = -1
+	}
+	if y0 < y1 {
+		sy = 1
+	} else {
+		sy = -1
+	}
+	err := dx - dy
+
+	var e2 int
+	for {
+		img.Set(x0, y0, color)
+		if x0 == x1 && y0 == y1 {
+			return
+		}
+		e2 = 2 * err
+		if e2 > -dy {
+			err = err - dy
+			x0 = x0 + sx
+		}
+		if e2 < dx {
+			err = err + dx
+			y0 = y0 + sy
+		}
+	}
+}

drawing/matrix.go

@@ -0,0 +1,220 @@
+package drawing
+
+import (
+	"math"
+)
+
+// Matrix represents an affine transformation
+type Matrix [6]float64
+
+const (
+	epsilon = 1e-6
+)
+
+// Determinant compute the determinant of the matrix
+func (tr Matrix) Determinant() float64 {
+	return tr[0]*tr[3] - tr[1]*tr[2]
+}
+
+// Transform applies the transformation matrix to points. It modify the points passed in parameter.
+func (tr Matrix) Transform(points []float64) {
+	for i, j := 0, 1; j < len(points); i, j = i+2, j+2 {
+		x := points[i]
+		y := points[j]
+		points[i] = x*tr[0] + y*tr[2] + tr[4]
+		points[j] = x*tr[1] + y*tr[3] + tr[5]
+	}
+}
+
+// TransformPoint applies the transformation matrix to point. It returns the point the transformed point.
+func (tr Matrix) TransformPoint(x, y float64) (xres, yres float64) {
+	xres = x*tr[0] + y*tr[2] + tr[4]
+	yres = x*tr[1] + y*tr[3] + tr[5]
+	return xres, yres
+}
+
+func minMax(x, y float64) (min, max float64) {
+	if x > y {
+		return y, x
+	}
+	return x, y
+}
+
+// TransformRectangle applies the transformation matrix to the rectangle represented by the min and the max point of the rectangle
+func (tr Matrix) TransformRectangle(x0, y0, x2, y2 float64) (nx0, ny0, nx2, ny2 float64) {
+	points := []float64{x0, y0, x2, y0, x2, y2, x0, y2}
+	tr.Transform(points)
+	points[0], points[2] = minMax(points[0], points[2])
+	points[4], points[6] = minMax(points[4], points[6])
+	points[1], points[3] = minMax(points[1], points[3])
+	points[5], points[7] = minMax(points[5], points[7])
+
+	nx0 = math.Min(points[0], points[4])
+	ny0 = math.Min(points[1], points[5])
+	nx2 = math.Max(points[2], points[6])
+	ny2 = math.Max(points[3], points[7])
+	return nx0, ny0, nx2, ny2
+}
+
+// InverseTransform applies the transformation inverse matrix to the rectangle represented by the min and the max point of the rectangle
+func (tr Matrix) InverseTransform(points []float64) {
+	d := tr.Determinant() // matrix determinant
+	for i, j := 0, 1; j < len(points); i, j = i+2, j+2 {
+		x := points[i]
+		y := points[j]
+		points[i] = ((x-tr[4])*tr[3] - (y-tr[5])*tr[2]) / d
+		points[j] = ((y-tr[5])*tr[0] - (x-tr[4])*tr[1]) / d
+	}
+}
+
+// InverseTransformPoint applies the transformation inverse matrix to point. It returns the point the transformed point.
+func (tr Matrix) InverseTransformPoint(x, y float64) (xres, yres float64) {
+	d := tr.Determinant() // matrix determinant
+	xres = ((x-tr[4])*tr[3] - (y-tr[5])*tr[2]) / d
+	yres = ((y-tr[5])*tr[0] - (x-tr[4])*tr[1]) / d
+	return xres, yres
+}
+
+// VectorTransform applies the transformation matrix to points without using the translation parameter of the affine matrix.
+// It modify the points passed in parameter.
+func (tr Matrix) VectorTransform(points []float64) {
+	for i, j := 0, 1; j < len(points); i, j = i+2, j+2 {
+		x := points[i]
+		y := points[j]
+		points[i] = x*tr[0] + y*tr[2]
+		points[j] = x*tr[1] + y*tr[3]
+	}
+}
+
+// NewIdentityMatrix creates an identity transformation matrix.
+func NewIdentityMatrix() Matrix {
+	return Matrix{1, 0, 0, 1, 0, 0}
+}
+
+// NewTranslationMatrix creates a transformation matrix with a translation tx and ty translation parameter
+func NewTranslationMatrix(tx, ty float64) Matrix {
+	return Matrix{1, 0, 0, 1, tx, ty}
+}
+
+// NewScaleMatrix creates a transformation matrix with a sx, sy scale factor
+func NewScaleMatrix(sx, sy float64) Matrix {
+	return Matrix{sx, 0, 0, sy, 0, 0}
+}
+
+// NewRotationMatrix creates a rotation transformation matrix. angle is in radian
+func NewRotationMatrix(angle float64) Matrix {
+	c := math.Cos(angle)
+	s := math.Sin(angle)
+	return Matrix{c, s, -s, c, 0, 0}
+}
+
+// NewMatrixFromRects creates a transformation matrix, combining a scale and a translation, that transform rectangle1 into rectangle2.
+func NewMatrixFromRects(rectangle1, rectangle2 [4]float64) Matrix {
+	xScale := (rectangle2[2] - rectangle2[0]) / (rectangle1[2] - rectangle1[0])
+	yScale := (rectangle2[3] - rectangle2[1]) / (rectangle1[3] - rectangle1[1])
+	xOffset := rectangle2[0] - (rectangle1[0] * xScale)
+	yOffset := rectangle2[1] - (rectangle1[1] * yScale)
+	return Matrix{xScale, 0, 0, yScale, xOffset, yOffset}
+}
+
+// Inverse computes the inverse matrix
+func (tr *Matrix) Inverse() {
+	d := tr.Determinant() // matrix determinant
+	tr0, tr1, tr2, tr3, tr4, tr5 := tr[0], tr[1], tr[2], tr[3], tr[4], tr[5]
+	tr[0] = tr3 / d
+	tr[1] = -tr1 / d
+	tr[2] = -tr2 / d
+	tr[3] = tr0 / d
+	tr[4] = (tr2*tr5 - tr3*tr4) / d
+	tr[5] = (tr1*tr4 - tr0*tr5) / d
+}
+
+// Copy copies the matrix.
+func (tr Matrix) Copy() Matrix {
+	var result Matrix
+	copy(result[:], tr[:])
+	return result
+}
+
+// Compose multiplies trToConcat x tr
+func (tr *Matrix) Compose(trToCompose Matrix) {
+	tr0, tr1, tr2, tr3, tr4, tr5 := tr[0], tr[1], tr[2], tr[3], tr[4], tr[5]
+	tr[0] = trToCompose[0]*tr0 + trToCompose[1]*tr2
+	tr[1] = trToCompose[1]*tr3 + trToCompose[0]*tr1
+	tr[2] = trToCompose[2]*tr0 + trToCompose[3]*tr2
+	tr[3] = trToCompose[3]*tr3 + trToCompose[2]*tr1
+	tr[4] = trToCompose[4]*tr0 + trToCompose[5]*tr2 + tr4
+	tr[5] = trToCompose[5]*tr3 + trToCompose[4]*tr1 + tr5
+}
+
+// Scale adds a scale to the matrix
+func (tr *Matrix) Scale(sx, sy float64) {
+	tr[0] = sx * tr[0]
+	tr[1] = sx * tr[1]
+	tr[2] = sy * tr[2]
+	tr[3] = sy * tr[3]
+}
+
+// Translate adds a translation to the matrix
+func (tr *Matrix) Translate(tx, ty float64) {
+	tr[4] = tx*tr[0] + ty*tr[2] + tr[4]
+	tr[5] = ty*tr[3] + tx*tr[1] + tr[5]
+}
+
+// Rotate adds a rotation to the matrix.
+func (tr *Matrix) Rotate(radians float64) {
+	c := math.Cos(radians)
+	s := math.Sin(radians)
+	t0 := c*tr[0] + s*tr[2]
+	t1 := s*tr[3] + c*tr[1]
+	t2 := c*tr[2] - s*tr[0]
+	t3 := c*tr[3] - s*tr[1]
+	tr[0] = t0
+	tr[1] = t1
+	tr[2] = t2
+	tr[3] = t3
+}
+
+// GetTranslation gets the matrix traslation.
+func (tr Matrix) GetTranslation() (x, y float64) {
+	return tr[4], tr[5]
+}
+
+// GetScaling gets the matrix scaling.
+func (tr Matrix) GetScaling() (x, y float64) {
+	return tr[0], tr[3]
+}
+
+// GetScale computes a scale for the matrix
+func (tr Matrix) GetScale() float64 {
+	x := 0.707106781*tr[0] + 0.707106781*tr[1]
+	y := 0.707106781*tr[2] + 0.707106781*tr[3]
+	return math.Sqrt(x*x + y*y)
+}
+
+// ******************** Testing ********************
+
+// Equals tests if a two transformation are equal. A tolerance is applied when comparing matrix elements.
+func (tr Matrix) Equals(tr2 Matrix) bool {
+	for i := 0; i < 6; i = i + 1 {
+		if !fequals(tr[i], tr2[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+// IsIdentity tests if a transformation is the identity transformation. A tolerance is applied when comparing matrix elements.
+func (tr Matrix) IsIdentity() bool {
+	return fequals(tr[4], 0) && fequals(tr[5], 0) && tr.IsTranslation()
+}
+
+// IsTranslation tests if a transformation is is a pure translation. A tolerance is applied when comparing matrix elements.
+func (tr Matrix) IsTranslation() bool {
+	return fequals(tr[0], 1) && fequals(tr[1], 0) && fequals(tr[2], 0) && fequals(tr[3], 1)
+}
+
+// fequals compares two floats. return true if the distance between the two floats is less than epsilon, false otherwise
+func fequals(float1, float2 float64) bool {
+	return math.Abs(float1-float2) <= epsilon
+}

drawing/painter.go

@@ -0,0 +1,31 @@
+package drawing
+
+import (
+	"image"
+	"image/color"
+
+	"golang.org/x/image/draw"
+	"golang.org/x/image/math/f64"
+
+	"github.com/golang/freetype/raster"
+)
+
+// Painter implements the freetype raster.Painter and has a SetColor method like the RGBAPainter
+type Painter interface {
+	raster.Painter
+	SetColor(color color.Color)
+}
+
+// DrawImage draws an image into dest using an affine transformation matrix, an op and a filter
+func DrawImage(src image.Image, dest draw.Image, tr Matrix, op draw.Op, filter ImageFilter) {
+	var transformer draw.Transformer
+	switch filter {
+	case LinearFilter:
+		transformer = draw.NearestNeighbor
+	case BilinearFilter:
+		transformer = draw.BiLinear
+	case BicubicFilter:
+		transformer = draw.CatmullRom
+	}
+	transformer.Transform(dest, f64.Aff3{tr[0], tr[1], tr[4], tr[2], tr[3], tr[5]}, src, src.Bounds(), op, nil)
+}

drawing/path.go

@@ -0,0 +1,186 @@
+package drawing
+
+import (
+	"fmt"
+	"math"
+)
+
+// PathBuilder describes the interface for path drawing.
+type PathBuilder interface {
+	// LastPoint returns the current point of the current sub path
+	LastPoint() (x, y float64)
+	// MoveTo creates a new subpath that start at the specified point
+	MoveTo(x, y float64)
+	// LineTo adds a line to the current subpath
+	LineTo(x, y float64)
+	// QuadCurveTo adds a quadratic Bézier curve to the current subpath
+	QuadCurveTo(cx, cy, x, y float64)
+	// CubicCurveTo adds a cubic Bézier curve to the current subpath
+	CubicCurveTo(cx1, cy1, cx2, cy2, x, y float64)
+	// ArcTo adds an arc to the current subpath
+	ArcTo(cx, cy, rx, ry, startAngle, angle float64)
+	// Close creates a line from the current point to the last MoveTo
+	// point (if not the same) and mark the path as closed so the
+	// first and last lines join nicely.
+	Close()
+}
+
+// PathComponent represents component of a path
+type PathComponent int
+
+const (
+	// MoveToComponent is a MoveTo component in a Path
+	MoveToComponent PathComponent = iota
+	// LineToComponent is a LineTo component in a Path
+	LineToComponent
+	// QuadCurveToComponent is a QuadCurveTo component in a Path
+	QuadCurveToComponent
+	// CubicCurveToComponent is a CubicCurveTo component in a Path
+	CubicCurveToComponent
+	// ArcToComponent is a ArcTo component in a Path
+	ArcToComponent
+	// CloseComponent is a ArcTo component in a Path
+	CloseComponent
+)
+
+// Path stores points
+type Path struct {
+	// Components is a slice of PathComponent in a Path and mark the role of each points in the Path
+	Components []PathComponent
+	// Points are combined with Components to have a specific role in the path
+	Points []float64
+	// Last Point of the Path
+	x, y float64
+}
+
+func (p *Path) appendToPath(cmd PathComponent, points ...float64) {
+	p.Components = append(p.Components, cmd)
+	p.Points = append(p.Points, points...)
+}
+
+// LastPoint returns the current point of the current path
+func (p *Path) LastPoint() (x, y float64) {
+	return p.x, p.y
+}
+
+// MoveTo starts a new path at (x, y) position
+func (p *Path) MoveTo(x, y float64) {
+	p.appendToPath(MoveToComponent, x, y)
+	p.x = x
+	p.y = y
+}
+
+// LineTo adds a line to the current path
+func (p *Path) LineTo(x, y float64) {
+	if len(p.Components) == 0 { //special case when no move has been done
+		p.MoveTo(0, 0)
+	}
+	p.appendToPath(LineToComponent, x, y)
+	p.x = x
+	p.y = y
+}
+
+// QuadCurveTo adds a quadratic bezier curve to the current path
+func (p *Path) QuadCurveTo(cx, cy, x, y float64) {
+	if len(p.Components) == 0 { //special case when no move has been done
+		p.MoveTo(0, 0)
+	}
+	p.appendToPath(QuadCurveToComponent, cx, cy, x, y)
+	p.x = x
+	p.y = y
+}
+
+// CubicCurveTo adds a cubic bezier curve to the current path
+func (p *Path) CubicCurveTo(cx1, cy1, cx2, cy2, x, y float64) {
+	if len(p.Components) == 0 { //special case when no move has been done
+		p.MoveTo(0, 0)
+	}
+	p.appendToPath(CubicCurveToComponent, cx1, cy1, cx2, cy2, x, y)
+	p.x = x
+	p.y = y
+}
+
+// ArcTo adds an arc to the path
+func (p *Path) ArcTo(cx, cy, rx, ry, startAngle, delta float64) {
+	endAngle := startAngle + delta
+	clockWise := true
+	if delta < 0 {
+		clockWise = false
+	}
+	// normalize
+	if clockWise {
+		for endAngle < startAngle {
+			endAngle += math.Pi * 2.0
+		}
+	} else {
+		for startAngle < endAngle {
+			startAngle += math.Pi * 2.0
+		}
+	}
+	startX := cx + math.Cos(startAngle)*rx
+	startY := cy + math.Sin(startAngle)*ry
+	if len(p.Components) > 0 {
+		p.LineTo(startX, startY)
+	} else {
+		p.MoveTo(startX, startY)
+	}
+	p.appendToPath(ArcToComponent, cx, cy, rx, ry, startAngle, delta)
+	p.x = cx + math.Cos(endAngle)*rx
+	p.y = cy + math.Sin(endAngle)*ry
+}
+
+// Close closes the current path
+func (p *Path) Close() {
+	p.appendToPath(CloseComponent)
+}
+
+// Copy make a clone of the current path and return it
+func (p *Path) Copy() (dest *Path) {
+	dest = new(Path)
+	dest.Components = make([]PathComponent, len(p.Components))
+	copy(dest.Components, p.Components)
+	dest.Points = make([]float64, len(p.Points))
+	copy(dest.Points, p.Points)
+	dest.x, dest.y = p.x, p.y
+	return dest
+}
+
+// Clear reset the path
+func (p *Path) Clear() {
+	p.Components = p.Components[0:0]
+	p.Points = p.Points[0:0]
+	return
+}
+
+// IsEmpty returns true if the path is empty
+func (p *Path) IsEmpty() bool {
+	return len(p.Components) == 0
+}
+
+// String returns a debug text view of the path
+func (p *Path) String() string {
+	s := ""
+	j := 0
+	for _, cmd := range p.Components {
+		switch cmd {
+		case MoveToComponent:
+			s += fmt.Sprintf("MoveTo: %f, %f\n", p.Points[j], p.Points[j+1])
+			j = j + 2
+		case LineToComponent:
+			s += fmt.Sprintf("LineTo: %f, %f\n", p.Points[j], p.Points[j+1])
+			j = j + 2
+		case QuadCurveToComponent:
+			s += fmt.Sprintf("QuadCurveTo: %f, %f, %f, %f\n", p.Points[j], p.Points[j+1], p.Points[j+2], p.Points[j+3])
+			j = j + 4
+		case CubicCurveToComponent:
+			s += fmt.Sprintf("CubicCurveTo: %f, %f, %f, %f, %f, %f\n", p.Points[j], p.Points[j+1], p.Points[j+2], p.Points[j+3], p.Points[j+4], p.Points[j+5])
+			j = j + 6
+		case ArcToComponent:
+			s += fmt.Sprintf("ArcTo: %f, %f, %f, %f, %f, %f\n", p.Points[j], p.Points[j+1], p.Points[j+2], p.Points[j+3], p.Points[j+4], p.Points[j+5])
+			j = j + 6
+		case CloseComponent:
+			s += "Close\n"
+		}
+	}
+	return s
+}

drawing/raster_graphic_context.go

@@ -0,0 +1,283 @@
+package drawing
+
+import (
+	"errors"
+	"image"
+	"image/color"
+	"math"
+
+	"github.com/golang/freetype/raster"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/draw"
+	"golang.org/x/image/font"
+	"golang.org/x/image/math/fixed"
+)
+
+// NewRasterGraphicContext creates a new Graphic context from an image.
+func NewRasterGraphicContext(img draw.Image) (*RasterGraphicContext, error) {
+	var painter Painter
+	switch selectImage := img.(type) {
+	case *image.RGBA:
+		painter = raster.NewRGBAPainter(selectImage)
+	default:
+		return nil, errors.New("NewRasterGraphicContext() :: invalid image type")
+	}
+	return NewRasterGraphicContextWithPainter(img, painter), nil
+}
+
+// NewRasterGraphicContextWithPainter creates a new Graphic context from an image and a Painter (see Freetype-go)
+func NewRasterGraphicContextWithPainter(img draw.Image, painter Painter) *RasterGraphicContext {
+	width, height := img.Bounds().Dx(), img.Bounds().Dy()
+	return &RasterGraphicContext{
+		NewStackGraphicContext(),
+		img,
+		painter,
+		raster.NewRasterizer(width, height),
+		raster.NewRasterizer(width, height),
+		&truetype.GlyphBuf{},
+		DefaultDPI,
+	}
+}
+
+// RasterGraphicContext is the implementation of GraphicContext for a raster image
+type RasterGraphicContext struct {
+	*StackGraphicContext
+	img              draw.Image
+	painter          Painter
+	fillRasterizer   *raster.Rasterizer
+	strokeRasterizer *raster.Rasterizer
+	glyphBuf         *truetype.GlyphBuf
+	DPI              float64
+}
+
+// SetDPI sets the screen resolution in dots per inch.
+func (rgc *RasterGraphicContext) SetDPI(dpi float64) {
+	rgc.DPI = dpi
+	rgc.recalc()
+}
+
+// GetDPI returns the resolution of the Image GraphicContext
+func (rgc *RasterGraphicContext) GetDPI() float64 {
+	return rgc.DPI
+}
+
+// Clear fills the current canvas with a default transparent color
+func (rgc *RasterGraphicContext) Clear() {
+	width, height := rgc.img.Bounds().Dx(), rgc.img.Bounds().Dy()
+	rgc.ClearRect(0, 0, width, height)
+}
+
+// ClearRect fills the current canvas with a default transparent color at the specified rectangle
+func (rgc *RasterGraphicContext) ClearRect(x1, y1, x2, y2 int) {
+	imageColor := image.NewUniform(rgc.current.FillColor)
+	draw.Draw(rgc.img, image.Rect(x1, y1, x2, y2), imageColor, image.ZP, draw.Over)
+}
+
+// DrawImage draws the raster image in the current canvas
+func (rgc *RasterGraphicContext) DrawImage(img image.Image) {
+	DrawImage(img, rgc.img, rgc.current.Tr, draw.Over, BilinearFilter)
+}
+
+// FillString draws the text at point (0, 0)
+func (rgc *RasterGraphicContext) FillString(text string) (cursor float64, err error) {
+	cursor, err = rgc.FillStringAt(text, 0, 0)
+	return
+}
+
+// FillStringAt draws the text at the specified point (x, y)
+func (rgc *RasterGraphicContext) FillStringAt(text string, x, y float64) (cursor float64, err error) {
+	cursor, err = rgc.CreateStringPath(text, x, y)
+	rgc.Fill()
+	return
+}
+
+// StrokeString draws the contour of the text at point (0, 0)
+func (rgc *RasterGraphicContext) StrokeString(text string) (cursor float64, err error) {
+	cursor, err = rgc.StrokeStringAt(text, 0, 0)
+	return
+}
+
+// StrokeStringAt draws the contour of the text at point (x, y)
+func (rgc *RasterGraphicContext) StrokeStringAt(text string, x, y float64) (cursor float64, err error) {
+	cursor, err = rgc.CreateStringPath(text, x, y)
+	rgc.Stroke()
+	return
+}
+
+func (rgc *RasterGraphicContext) drawGlyph(glyph truetype.Index, dx, dy float64) error {
+	if err := rgc.glyphBuf.Load(rgc.current.Font, fixed.Int26_6(rgc.current.Scale), glyph, font.HintingNone); err != nil {
+		return err
+	}
+	e0 := 0
+	for _, e1 := range rgc.glyphBuf.Ends {
+		DrawContour(rgc, rgc.glyphBuf.Points[e0:e1], dx, dy)
+		e0 = e1
+	}
+	return nil
+}
+
+// CreateStringPath creates a path from the string s at x, y, and returns the string width.
+// The text is placed so that the left edge of the em square of the first character of s
+// and the baseline intersect at x, y. The majority of the affected pixels will be
+// above and to the right of the point, but some may be below or to the left.
+// For example, drawing a string that starts with a 'J' in an italic font may
+// affect pixels below and left of the point.
+func (rgc *RasterGraphicContext) CreateStringPath(s string, x, y float64) (cursor float64, err error) {
+	f := rgc.GetFont()
+	if f == nil {
+		err = errors.New("No font loaded, cannot continue")
+		return
+	}
+	rgc.recalc()
+
+	startx := x
+	prev, hasPrev := truetype.Index(0), false
+	for _, rc := range s {
+		index := f.Index(rc)
+		if hasPrev {
+			x += fUnitsToFloat64(f.Kern(fixed.Int26_6(rgc.current.Scale), prev, index))
+		}
+		err = rgc.drawGlyph(index, x, y)
+		if err != nil {
+			cursor = x - startx
+			return
+		}
+		x += fUnitsToFloat64(f.HMetric(fixed.Int26_6(rgc.current.Scale), index).AdvanceWidth)
+		prev, hasPrev = index, true
+	}
+	cursor = x - startx
+	return
+}
+
+// GetStringBounds returns the approximate pixel bounds of a string.
+func (rgc *RasterGraphicContext) GetStringBounds(s string) (left, top, right, bottom float64, err error) {
+	f := rgc.GetFont()
+	if f == nil {
+		err = errors.New("No font loaded, cannot continue")
+		return
+	}
+	rgc.recalc()
+
+	left = math.MaxFloat64
+	top = math.MaxFloat64
+
+	cursor := 0.0
+	prev, hasPrev := truetype.Index(0), false
+	for _, rc := range s {
+		index := f.Index(rc)
+		if hasPrev {
+			cursor += fUnitsToFloat64(f.Kern(fixed.Int26_6(rgc.current.Scale), prev, index))
+		}
+
+		if err = rgc.glyphBuf.Load(rgc.current.Font, fixed.Int26_6(rgc.current.Scale), index, font.HintingNone); err != nil {
+			return
+		}
+		e0 := 0
+		for _, e1 := range rgc.glyphBuf.Ends {
+			ps := rgc.glyphBuf.Points[e0:e1]
+			for _, p := range ps {
+				x, y := pointToF64Point(p)
+				top = math.Min(top, y)
+				bottom = math.Max(bottom, y)
+				left = math.Min(left, x+cursor)
+				right = math.Max(right, x+cursor)
+			}
+			e0 = e1
+		}
+		cursor += fUnitsToFloat64(f.HMetric(fixed.Int26_6(rgc.current.Scale), index).AdvanceWidth)
+		prev, hasPrev = index, true
+	}
+	return
+}
+
+// recalc recalculates scale and bounds values from the font size, screen
+// resolution and font metrics, and invalidates the glyph cache.
+func (rgc *RasterGraphicContext) recalc() {
+	rgc.current.Scale = rgc.current.FontSizePoints * float64(rgc.DPI)
+}
+
+// SetFont sets the font used to draw text.
+func (rgc *RasterGraphicContext) SetFont(font *truetype.Font) {
+	rgc.current.Font = font
+}
+
+// GetFont returns the font used to draw text.
+func (rgc *RasterGraphicContext) GetFont() *truetype.Font {
+	return rgc.current.Font
+}
+
+// SetFontSize sets the font size in points (as in ``a 12 point font'').
+func (rgc *RasterGraphicContext) SetFontSize(fontSizePoints float64) {
+	rgc.current.FontSizePoints = fontSizePoints
+	rgc.recalc()
+}
+
+func (rgc *RasterGraphicContext) paint(rasterizer *raster.Rasterizer, color color.Color) {
+	rgc.painter.SetColor(color)
+	rasterizer.Rasterize(rgc.painter)
+	rasterizer.Clear()
+	rgc.current.Path.Clear()
+}
+
+// Stroke strokes the paths with the color specified by SetStrokeColor
+func (rgc *RasterGraphicContext) Stroke(paths ...*Path) {
+	paths = append(paths, rgc.current.Path)
+	rgc.strokeRasterizer.UseNonZeroWinding = true
+
+	stroker := NewLineStroker(rgc.current.Cap, rgc.current.Join, Transformer{Tr: rgc.current.Tr, Flattener: FtLineBuilder{Adder: rgc.strokeRasterizer}})
+	stroker.HalfLineWidth = rgc.current.LineWidth / 2
+
+	var liner Flattener
+	if rgc.current.Dash != nil && len(rgc.current.Dash) > 0 {
+		liner = NewDashVertexConverter(rgc.current.Dash, rgc.current.DashOffset, stroker)
+	} else {
+		liner = stroker
+	}
+	for _, p := range paths {
+		Flatten(p, liner, rgc.current.Tr.GetScale())
+	}
+
+	rgc.paint(rgc.strokeRasterizer, rgc.current.StrokeColor)
+}
+
+// Fill fills the paths with the color specified by SetFillColor
+func (rgc *RasterGraphicContext) Fill(paths ...*Path) {
+	paths = append(paths, rgc.current.Path)
+	rgc.fillRasterizer.UseNonZeroWinding = rgc.current.FillRule == FillRuleWinding
+
+	flattener := Transformer{Tr: rgc.current.Tr, Flattener: FtLineBuilder{Adder: rgc.fillRasterizer}}
+	for _, p := range paths {
+		Flatten(p, flattener, rgc.current.Tr.GetScale())
+	}
+
+	rgc.paint(rgc.fillRasterizer, rgc.current.FillColor)
+}
+
+// FillStroke first fills the paths and than strokes them
+func (rgc *RasterGraphicContext) FillStroke(paths ...*Path) {
+	paths = append(paths, rgc.current.Path)
+	rgc.fillRasterizer.UseNonZeroWinding = rgc.current.FillRule == FillRuleWinding
+	rgc.strokeRasterizer.UseNonZeroWinding = true
+
+	flattener := Transformer{Tr: rgc.current.Tr, Flattener: FtLineBuilder{Adder: rgc.fillRasterizer}}
+
+	stroker := NewLineStroker(rgc.current.Cap, rgc.current.Join, Transformer{Tr: rgc.current.Tr, Flattener: FtLineBuilder{Adder: rgc.strokeRasterizer}})
+	stroker.HalfLineWidth = rgc.current.LineWidth / 2
+
+	var liner Flattener
+	if rgc.current.Dash != nil && len(rgc.current.Dash) > 0 {
+		liner = NewDashVertexConverter(rgc.current.Dash, rgc.current.DashOffset, stroker)
+	} else {
+		liner = stroker
+	}
+
+	demux := DemuxFlattener{Flatteners: []Flattener{flattener, liner}}
+	for _, p := range paths {
+		Flatten(p, demux, rgc.current.Tr.GetScale())
+	}
+
+	// Fill
+	rgc.paint(rgc.fillRasterizer, rgc.current.FillColor)
+	// Stroke
+	rgc.paint(rgc.strokeRasterizer, rgc.current.StrokeColor)
+}

drawing/stack_graphic_context.go

@@ -0,0 +1,211 @@
+package drawing
+
+import (
+	"image"
+	"image/color"
+
+	"github.com/golang/freetype/truetype"
+)
+
+// StackGraphicContext is a context that does thngs.
+type StackGraphicContext struct {
+	current *ContextStack
+}
+
+// ContextStack is a graphic context implementation.
+type ContextStack struct {
+	Tr          Matrix
+	Path        *Path
+	LineWidth   float64
+	Dash        []float64
+	DashOffset  float64
+	StrokeColor color.Color
+	FillColor   color.Color
+	FillRule    FillRule
+	Cap         LineCap
+	Join        LineJoin
+
+	FontSizePoints float64
+	Font           *truetype.Font
+
+	Scale float64
+
+	Previous *ContextStack
+}
+
+// NewStackGraphicContext Create a new Graphic context from an image
+func NewStackGraphicContext() *StackGraphicContext {
+	gc := &StackGraphicContext{}
+	gc.current = new(ContextStack)
+	gc.current.Tr = NewIdentityMatrix()
+	gc.current.Path = new(Path)
+	gc.current.LineWidth = 1.0
+	gc.current.StrokeColor = image.Black
+	gc.current.FillColor = image.White
+	gc.current.Cap = RoundCap
+	gc.current.FillRule = FillRuleEvenOdd
+	gc.current.Join = RoundJoin
+	gc.current.FontSizePoints = 10
+	return gc
+}
+
+// GetMatrixTransform returns the matrix transform.
+func (gc *StackGraphicContext) GetMatrixTransform() Matrix {
+	return gc.current.Tr
+}
+
+// SetMatrixTransform sets the matrix transform.
+func (gc *StackGraphicContext) SetMatrixTransform(tr Matrix) {
+	gc.current.Tr = tr
+}
+
+// ComposeMatrixTransform composes a transform into the current transform.
+func (gc *StackGraphicContext) ComposeMatrixTransform(tr Matrix) {
+	gc.current.Tr.Compose(tr)
+}
+
+// Rotate rotates the matrix transform by an angle in degrees.
+func (gc *StackGraphicContext) Rotate(angle float64) {
+	gc.current.Tr.Rotate(angle)
+}
+
+// Translate translates a transform.
+func (gc *StackGraphicContext) Translate(tx, ty float64) {
+	gc.current.Tr.Translate(tx, ty)
+}
+
+// Scale scales a transform.
+func (gc *StackGraphicContext) Scale(sx, sy float64) {
+	gc.current.Tr.Scale(sx, sy)
+}
+
+// SetStrokeColor sets the stroke color.
+func (gc *StackGraphicContext) SetStrokeColor(c color.Color) {
+	gc.current.StrokeColor = c
+}
+
+// SetFillColor sets the fill color.
+func (gc *StackGraphicContext) SetFillColor(c color.Color) {
+	gc.current.FillColor = c
+}
+
+// SetFillRule sets the fill rule.
+func (gc *StackGraphicContext) SetFillRule(f FillRule) {
+	gc.current.FillRule = f
+}
+
+// SetLineWidth sets the line width.
+func (gc *StackGraphicContext) SetLineWidth(lineWidth float64) {
+	gc.current.LineWidth = lineWidth
+}
+
+// SetLineCap sets the line cap.
+func (gc *StackGraphicContext) SetLineCap(cap LineCap) {
+	gc.current.Cap = cap
+}
+
+// SetLineJoin sets the line join.
+func (gc *StackGraphicContext) SetLineJoin(join LineJoin) {
+	gc.current.Join = join
+}
+
+// SetLineDash sets the line dash.
+func (gc *StackGraphicContext) SetLineDash(dash []float64, dashOffset float64) {
+	gc.current.Dash = dash
+	gc.current.DashOffset = dashOffset
+}
+
+// SetFontSize sets the font size.
+func (gc *StackGraphicContext) SetFontSize(fontSizePoints float64) {
+	gc.current.FontSizePoints = fontSizePoints
+}
+
+// GetFontSize gets the font size.
+func (gc *StackGraphicContext) GetFontSize() float64 {
+	return gc.current.FontSizePoints
+}
+
+// SetFont sets the current font.
+func (gc *StackGraphicContext) SetFont(f *truetype.Font) {
+	gc.current.Font = f
+}
+
+// GetFont returns the font.
+func (gc *StackGraphicContext) GetFont() *truetype.Font {
+	return gc.current.Font
+}
+
+// BeginPath starts a new path.
+func (gc *StackGraphicContext) BeginPath() {
+	gc.current.Path.Clear()
+}
+
+// IsEmpty returns if the path is empty.
+func (gc *StackGraphicContext) IsEmpty() bool {
+	return gc.current.Path.IsEmpty()
+}
+
+// LastPoint returns the last point on the path.
+func (gc *StackGraphicContext) LastPoint() (x float64, y float64) {
+	return gc.current.Path.LastPoint()
+}
+
+// MoveTo moves the cursor for a path.
+func (gc *StackGraphicContext) MoveTo(x, y float64) {
+	gc.current.Path.MoveTo(x, y)
+}
+
+// LineTo draws a line.
+func (gc *StackGraphicContext) LineTo(x, y float64) {
+	gc.current.Path.LineTo(x, y)
+}
+
+// QuadCurveTo draws a quad curve.
+func (gc *StackGraphicContext) QuadCurveTo(cx, cy, x, y float64) {
+	gc.current.Path.QuadCurveTo(cx, cy, x, y)
+}
+
+// CubicCurveTo draws a cubic curve.
+func (gc *StackGraphicContext) CubicCurveTo(cx1, cy1, cx2, cy2, x, y float64) {
+	gc.current.Path.CubicCurveTo(cx1, cy1, cx2, cy2, x, y)
+}
+
+// ArcTo draws an arc.
+func (gc *StackGraphicContext) ArcTo(cx, cy, rx, ry, startAngle, delta float64) {
+	gc.current.Path.ArcTo(cx, cy, rx, ry, startAngle, delta)
+}
+
+// Close closes a path.
+func (gc *StackGraphicContext) Close() {
+	gc.current.Path.Close()
+}
+
+// Save pushes a context onto the stack.
+func (gc *StackGraphicContext) Save() {
+	context := new(ContextStack)
+	context.FontSizePoints = gc.current.FontSizePoints
+	context.Font = gc.current.Font
+	context.LineWidth = gc.current.LineWidth
+	context.StrokeColor = gc.current.StrokeColor
+	context.FillColor = gc.current.FillColor
+	context.FillRule = gc.current.FillRule
+	context.Dash = gc.current.Dash
+	context.DashOffset = gc.current.DashOffset
+	context.Cap = gc.current.Cap
+	context.Join = gc.current.Join
+	context.Path = gc.current.Path.Copy()
+	context.Font = gc.current.Font
+	context.Scale = gc.current.Scale
+	copy(context.Tr[:], gc.current.Tr[:])
+	context.Previous = gc.current
+	gc.current = context
+}
+
+// Restore restores the previous context.
+func (gc *StackGraphicContext) Restore() {
+	if gc.current.Previous != nil {
+		oldContext := gc.current
+		gc.current = gc.current.Previous
+		oldContext.Previous = nil
+	}
+}

drawing/stroker.go

@@ -0,0 +1,85 @@
+// Copyright 2010 The draw2d Authors. All rights reserved.
+// created: 13/12/2010 by Laurent Le Goff
+
+package drawing
+
+// NewLineStroker creates a new line stroker.
+func NewLineStroker(c LineCap, j LineJoin, flattener Flattener) *LineStroker {
+	l := new(LineStroker)
+	l.Flattener = flattener
+	l.HalfLineWidth = 0.5
+	l.Cap = c
+	l.Join = j
+	return l
+}
+
+// LineStroker draws the stroke portion of a line.
+type LineStroker struct {
+	Flattener     Flattener
+	HalfLineWidth float64
+	Cap           LineCap
+	Join          LineJoin
+	vertices      []float64
+	rewind        []float64
+	x, y, nx, ny  float64
+}
+
+// MoveTo implements the path builder interface.
+func (l *LineStroker) MoveTo(x, y float64) {
+	l.x, l.y = x, y
+}
+
+// LineTo implements the path builder interface.
+func (l *LineStroker) LineTo(x, y float64) {
+	l.line(l.x, l.y, x, y)
+}
+
+// LineJoin implements the path builder interface.
+func (l *LineStroker) LineJoin() {}
+
+func (l *LineStroker) line(x1, y1, x2, y2 float64) {
+	dx := (x2 - x1)
+	dy := (y2 - y1)
+	d := vectorDistance(dx, dy)
+	if d != 0 {
+		nx := dy * l.HalfLineWidth / d
+		ny := -(dx * l.HalfLineWidth / d)
+		l.appendVertex(x1+nx, y1+ny, x2+nx, y2+ny, x1-nx, y1-ny, x2-nx, y2-ny)
+		l.x, l.y, l.nx, l.ny = x2, y2, nx, ny
+	}
+}
+
+// Close implements the path builder interface.
+func (l *LineStroker) Close() {
+	if len(l.vertices) > 1 {
+		l.appendVertex(l.vertices[0], l.vertices[1], l.rewind[0], l.rewind[1])
+	}
+}
+
+// End implements the path builder interface.
+func (l *LineStroker) End() {
+	if len(l.vertices) > 1 {
+		l.Flattener.MoveTo(l.vertices[0], l.vertices[1])
+		for i, j := 2, 3; j < len(l.vertices); i, j = i+2, j+2 {
+			l.Flattener.LineTo(l.vertices[i], l.vertices[j])
+		}
+	}
+	for i, j := len(l.rewind)-2, len(l.rewind)-1; j > 0; i, j = i-2, j-2 {
+		l.Flattener.LineTo(l.rewind[i], l.rewind[j])
+	}
+	if len(l.vertices) > 1 {
+		l.Flattener.LineTo(l.vertices[0], l.vertices[1])
+	}
+	l.Flattener.End()
+	// reinit vertices
+	l.vertices = l.vertices[0:0]
+	l.rewind = l.rewind[0:0]
+	l.x, l.y, l.nx, l.ny = 0, 0, 0, 0
+
+}
+
+func (l *LineStroker) appendVertex(vertices ...float64) {
+	s := len(vertices) / 2
+	l.vertices = append(l.vertices, vertices[:s]...)
+	l.rewind = append(l.rewind, vertices[s:]...)
+}

drawing/text.go

@@ -0,0 +1,67 @@
+package drawing
+
+import (
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/math/fixed"
+)
+
+// DrawContour draws the given closed contour at the given sub-pixel offset.
+func DrawContour(path PathBuilder, ps []truetype.Point, dx, dy float64) {
+	if len(ps) == 0 {
+		return
+	}
+	startX, startY := pointToF64Point(ps[0])
+	path.MoveTo(startX+dx, startY+dy)
+	q0X, q0Y, on0 := startX, startY, true
+	for _, p := range ps[1:] {
+		qX, qY := pointToF64Point(p)
+		on := p.Flags&0x01 != 0
+		if on {
+			if on0 {
+				path.LineTo(qX+dx, qY+dy)
+			} else {
+				path.QuadCurveTo(q0X+dx, q0Y+dy, qX+dx, qY+dy)
+			}
+		} else if !on0 {
+			midX := (q0X + qX) / 2
+			midY := (q0Y + qY) / 2
+			path.QuadCurveTo(q0X+dx, q0Y+dy, midX+dx, midY+dy)
+		}
+		q0X, q0Y, on0 = qX, qY, on
+	}
+	// Close the curve.
+	if on0 {
+		path.LineTo(startX+dx, startY+dy)
+	} else {
+		path.QuadCurveTo(q0X+dx, q0Y+dy, startX+dx, startY+dy)
+	}
+}
+
+// FontExtents contains font metric information.
+type FontExtents struct {
+	// Ascent is the distance that the text
+	// extends above the baseline.
+	Ascent float64
+
+	// Descent is the distance that the text
+	// extends below the baseline.  The descent
+	// is given as a negative value.
+	Descent float64
+
+	// Height is the distance from the lowest
+	// descending point to the highest ascending
+	// point.
+	Height float64
+}
+
+// Extents returns the FontExtents for a font.
+// TODO needs to read this https://developer.apple.com/fonts/TrueType-Reference-Manual/RM02/Chap2.html#intro
+func Extents(font *truetype.Font, size float64) FontExtents {
+	bounds := font.Bounds(fixed.Int26_6(font.FUnitsPerEm()))
+	scale := size / float64(font.FUnitsPerEm())
+	return FontExtents{
+		Ascent:  float64(bounds.Max.Y) * scale,
+		Descent: float64(bounds.Min.Y) * scale,
+		Height:  float64(bounds.Max.Y-bounds.Min.Y) * scale,
+	}
+}

drawing/transformer.go

@@ -0,0 +1,39 @@
+// Copyright 2010 The draw2d Authors. All rights reserved.
+// created: 13/12/2010 by Laurent Le Goff
+
+package drawing
+
+// Transformer apply the Matrix transformation tr
+type Transformer struct {
+	Tr        Matrix
+	Flattener Flattener
+}
+
+// MoveTo implements the path builder interface.
+func (t Transformer) MoveTo(x, y float64) {
+	u := x*t.Tr[0] + y*t.Tr[2] + t.Tr[4]
+	v := x*t.Tr[1] + y*t.Tr[3] + t.Tr[5]
+	t.Flattener.MoveTo(u, v)
+}
+
+// LineTo implements the path builder interface.
+func (t Transformer) LineTo(x, y float64) {
+	u := x*t.Tr[0] + y*t.Tr[2] + t.Tr[4]
+	v := x*t.Tr[1] + y*t.Tr[3] + t.Tr[5]
+	t.Flattener.LineTo(u, v)
+}
+
+// LineJoin implements the path builder interface.
+func (t Transformer) LineJoin() {
+	t.Flattener.LineJoin()
+}
+
+// Close implements the path builder interface.
+func (t Transformer) Close() {
+	t.Flattener.Close()
+}
+
+// End implements the path builder interface.
+func (t Transformer) End() {
+	t.Flattener.End()
+}

drawing/util.go

@@ -0,0 +1,68 @@
+package drawing
+
+import (
+	"math"
+
+	"golang.org/x/image/math/fixed"
+
+	"github.com/golang/freetype/raster"
+	"github.com/golang/freetype/truetype"
+)
+
+// PixelsToPoints returns the points for a given number of pixels at a DPI.
+func PixelsToPoints(dpi, pixels float64) (points float64) {
+	points = (pixels * 72.0) / dpi
+	return
+}
+
+// PointsToPixels returns the pixels for a given number of points at a DPI.
+func PointsToPixels(dpi, points float64) (pixels float64) {
+	pixels = (points * dpi) / 72.0
+	return
+}
+
+func abs(i int) int {
+	if i < 0 {
+		return -i
+	}
+	return i
+}
+
+func distance(x1, y1, x2, y2 float64) float64 {
+	return vectorDistance(x2-x1, y2-y1)
+}
+
+func vectorDistance(dx, dy float64) float64 {
+	return float64(math.Sqrt(dx*dx + dy*dy))
+}
+
+func toFtCap(c LineCap) raster.Capper {
+	switch c {
+	case RoundCap:
+		return raster.RoundCapper
+	case ButtCap:
+		return raster.ButtCapper
+	case SquareCap:
+		return raster.SquareCapper
+	}
+	return raster.RoundCapper
+}
+
+func toFtJoin(j LineJoin) raster.Joiner {
+	switch j {
+	case RoundJoin:
+		return raster.RoundJoiner
+	case BevelJoin:
+		return raster.BevelJoiner
+	}
+	return raster.RoundJoiner
+}
+
+func pointToF64Point(p truetype.Point) (x, y float64) {
+	return fUnitsToFloat64(p.X), -fUnitsToFloat64(p.Y)
+}
+
+func fUnitsToFloat64(x fixed.Int26_6) float64 {
+	scaled := x << 2
+	return float64(scaled/256) + float64(scaled%256)/256.0
+}

ema_series.go

@@ -0,0 +1,131 @@
+package chart
+
+import "fmt"
+
+const (
+	// DefaultEMAPeriod is the default EMA period used in the sigma calculation.
+	DefaultEMAPeriod = 12
+)
+
+// Interface Assertions.
+var (
+	_ Series              = (*EMASeries)(nil)
+	_ FirstValuesProvider = (*EMASeries)(nil)
+	_ LastValuesProvider  = (*EMASeries)(nil)
+)
+
+// EMASeries is a computed series.
+type EMASeries struct {
+	Name  string
+	Style Style
+	YAxis YAxisType
+
+	Period      int
+	InnerSeries ValuesProvider
+
+	cache []float64
+}
+
+// GetName returns the name of the time series.
+func (ema EMASeries) GetName() string {
+	return ema.Name
+}
+
+// GetStyle returns the line style.
+func (ema EMASeries) GetStyle() Style {
+	return ema.Style
+}
+
+// GetYAxis returns which YAxis the series draws on.
+func (ema EMASeries) GetYAxis() YAxisType {
+	return ema.YAxis
+}
+
+// GetPeriod returns the window size.
+func (ema EMASeries) GetPeriod() int {
+	if ema.Period == 0 {
+		return DefaultEMAPeriod
+	}
+	return ema.Period
+}
+
+// Len returns the number of elements in the series.
+func (ema EMASeries) Len() int {
+	return ema.InnerSeries.Len()
+}
+
+// GetSigma returns the smoothing factor for the serise.
+func (ema EMASeries) GetSigma() float64 {
+	return 2.0 / (float64(ema.GetPeriod()) + 1)
+}
+
+// GetValues gets a value at a given index.
+func (ema *EMASeries) GetValues(index int) (x, y float64) {
+	if ema.InnerSeries == nil {
+		return
+	}
+	if len(ema.cache) == 0 {
+		ema.ensureCachedValues()
+	}
+	vx, _ := ema.InnerSeries.GetValues(index)
+	x = vx
+	y = ema.cache[index]
+	return
+}
+
+// GetFirstValues computes the first moving average value.
+func (ema *EMASeries) GetFirstValues() (x, y float64) {
+	if ema.InnerSeries == nil {
+		return
+	}
+	if len(ema.cache) == 0 {
+		ema.ensureCachedValues()
+	}
+	x, _ = ema.InnerSeries.GetValues(0)
+	y = ema.cache[0]
+	return
+}
+
+// GetLastValues computes the last moving average value but walking back window size samples,
+// and recomputing the last moving average chunk.
+func (ema *EMASeries) GetLastValues() (x, y float64) {
+	if ema.InnerSeries == nil {
+		return
+	}
+	if len(ema.cache) == 0 {
+		ema.ensureCachedValues()
+	}
+	lastIndex := ema.InnerSeries.Len() - 1
+	x, _ = ema.InnerSeries.GetValues(lastIndex)
+	y = ema.cache[lastIndex]
+	return
+}
+
+func (ema *EMASeries) ensureCachedValues() {
+	seriesLength := ema.InnerSeries.Len()
+	ema.cache = make([]float64, seriesLength)
+	sigma := ema.GetSigma()
+	for x := 0; x < seriesLength; x++ {
+		_, y := ema.InnerSeries.GetValues(x)
+		if x == 0 {
+			ema.cache[x] = y
+			continue
+		}
+		previousEMA := ema.cache[x-1]
+		ema.cache[x] = ((y - previousEMA) * sigma) + previousEMA
+	}
+}
+
+// Render renders the series.
+func (ema *EMASeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) {
+	style := ema.Style.InheritFrom(defaults)
+	Draw.LineSeries(r, canvasBox, xrange, yrange, style, ema)
+}
+
+// Validate validates the series.
+func (ema *EMASeries) Validate() error {
+	if ema.InnerSeries == nil {
+		return fmt.Errorf("ema series requires InnerSeries to be set")
+	}
+	return nil
+}

ema_series_test.go

@@ -0,0 +1,105 @@
+package chart
+
+import (
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+var (
+	emaXValues = LinearRange(1.0, 50.0)
+	emaYValues = []float64{
+		1, 2, 3, 4, 5, 4, 3, 2,
+		1, 2, 3, 4, 5, 4, 3, 2,
+		1, 2, 3, 4, 5, 4, 3, 2,
+		1, 2, 3, 4, 5, 4, 3, 2,
+		1, 2, 3, 4, 5, 4, 3, 2,
+		1, 2, 3, 4, 5, 4, 3, 2,
+		1, 2,
+	}
+	emaExpected = []float64{
+		1,
+		1.074074074,
+		1.216735254,
+		1.422903013,
+		1.68787316,
+		1.859141815,
+		1.943649828,
+		1.947823915,
+		1.877614736,
+		1.886680311,
+		1.969148437,
+		2.119581886,
+		2.33294619,
+		2.456431658,
+		2.496695979,
+		2.459903685,
+		2.351762671,
+		2.325706177,
+		2.375653867,
+		2.495975803,
+		2.681459077,
+		2.779128775,
+		2.795489607,
+		2.73656445,
+		2.607930047,
+		2.562898191,
+		2.595276103,
+		2.699329725,
+		2.869749746,
+		2.953471987,
+		2.956918506,
+		2.886035654,
+		2.746329309,
+		2.691045657,
+		2.713931163,
+		2.809195522,
+		2.971477335,
+		3.047664199,
+		3.044133518,
+		2.966790294,
+		2.821102124,
+		2.760279745,
+		2.778036801,
+		2.868552593,
+		3.026437586,
+		3.098553321,
+		3.091253075,
+		3.010419514,
+		2.86149955,
+		2.797684768,
+	}
+	emaDelta = 0.0001
+)
+
+func TestEMASeries(t *testing.T) {
+	// replaced new assertions helper
+
+	mockSeries := mockValuesProvider{
+		emaXValues,
+		emaYValues,
+	}
+	testutil.AssertEqual(t, 50, mockSeries.Len())
+
+	ema := &EMASeries{
+		InnerSeries: mockSeries,
+		Period:      26,
+	}
+
+	sig := ema.GetSigma()
+	testutil.AssertEqual(t, 2.0/(26.0+1), sig)
+
+	var yvalues []float64
+	for x := 0; x < ema.Len(); x++ {
+		_, y := ema.GetValues(x)
+		yvalues = append(yvalues, y)
+	}
+
+	for index, yv := range yvalues {
+		testutil.AssertInDelta(t, yv, emaExpected[index], emaDelta)
+	}
+
+	lvx, lvy := ema.GetLastValues()
+	testutil.AssertEqual(t, 50.0, lvx)
+	testutil.AssertInDelta(t, lvy, emaExpected[49], emaDelta)
+}

examples/annotations/main.go

@@ -0,0 +1,44 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+	/*
+	   In this example we add an `Annotation` series, which is a special type of series that
+	   draws annotation labels at given X and Y values (as translated by their respective ranges).
+
+	   It is important to not that the chart automatically sizes the canvas box to fit the annotations,
+	   As well as automatically assign a series color for the `Stroke` or border component of the series.
+
+	   The annotation series is most often used by the original author to show the last value of another series, but
+	   they can be used in other capacities as well.
+	*/
+
+	graph := chart.Chart{
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+			chart.AnnotationSeries{
+				Annotations: []chart.Value2{
+					{XValue: 1.0, YValue: 1.0, Label: "One"},
+					{XValue: 2.0, YValue: 2.0, Label: "Two"},
+					{XValue: 3.0, YValue: 3.0, Label: "Three"},
+					{XValue: 4.0, YValue: 4.0, Label: "Four"},
+					{XValue: 5.0, YValue: 5.0, Label: "Five"},
+				},
+			},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/axes/main.go

@@ -0,0 +1,34 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	chart "github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+
+	/*
+	   The below will draw the same chart as the `basic` example, except with both the x and y axes turned on.
+	   In this case, both the x and y axis ticks are generated automatically, the x and y ranges are established automatically, the canvas "box" is adjusted to fit the space the axes occupy so as not to clip.
+	*/
+
+	graph := chart.Chart{
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					StrokeColor: chart.GetDefaultColor(0).WithAlpha(64),
+					FillColor:   chart.GetDefaultColor(0).WithAlpha(64),
+				},
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/axes_labels/main.go

@@ -0,0 +1,40 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	chart "github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+
+	/*
+	   The below will draw the same chart as the `basic` example, except with both the x and y axes turned on.
+	   In this case, both the x and y axis ticks are generated automatically, the x and y ranges are established automatically, the canvas "box" is adjusted to fit the space the axes occupy so as not to clip.
+	*/
+
+	graph := chart.Chart{
+		XAxis: chart.XAxis{
+			Name: "The XAxis",
+		},
+		YAxis: chart.YAxis{
+			Name: "The YAxis",
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					StrokeColor: chart.GetDefaultColor(0).WithAlpha(64),
+					FillColor:   chart.GetDefaultColor(0).WithAlpha(64),
+				},
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/bar_chart/main.go

@@ -0,0 +1,35 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+	graph := chart.BarChart{
+		Title: "Test Bar Chart",
+		Background: chart.Style{
+			Padding: chart.Box{
+				Top: 40,
+			},
+		},
+		Height:   512,
+		BarWidth: 60,
+		Bars: []chart.Value{
+			{Value: 5.25, Label: "Blue"},
+			{Value: 4.88, Label: "Green"},
+			{Value: 4.74, Label: "Gray"},
+			{Value: 3.22, Label: "Orange"},
+			{Value: 3, Label: "Test"},
+			{Value: 2.27, Label: "??"},
+			{Value: 1, Label: "!!"},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/bar_chart_base_value/main.go

@@ -0,0 +1,62 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+	"github.com/wcharczuk/go-chart/v2/drawing"
+)
+
+func main() {
+	profitStyle := chart.Style{
+		FillColor:   drawing.ColorFromHex("13c158"),
+		StrokeColor: drawing.ColorFromHex("13c158"),
+		StrokeWidth: 0,
+	}
+
+	lossStyle := chart.Style{
+		FillColor:   drawing.ColorFromHex("c11313"),
+		StrokeColor: drawing.ColorFromHex("c11313"),
+		StrokeWidth: 0,
+	}
+
+	sbc := chart.BarChart{
+		Title: "Bar Chart Using BaseValue",
+		Background: chart.Style{
+			Padding: chart.Box{
+				Top: 40,
+			},
+		},
+		Height:   512,
+		BarWidth: 60,
+		YAxis: chart.YAxis{
+			Ticks: []chart.Tick{
+				{Value: -4.0, Label: "-4"},
+				{Value: -2.0, Label: "-2"},
+				{Value: 0, Label: "0"},
+				{Value: 2.0, Label: "2"},
+				{Value: 4.0, Label: "4"},
+				{Value: 6.0, Label: "6"},
+				{Value: 8.0, Label: "8"},
+				{Value: 10.0, Label: "10"},
+				{Value: 12.0, Label: "12"},
+			},
+		},
+		UseBaseValue: true,
+		BaseValue:    0.0,
+		Bars: []chart.Value{
+			{Value: 10.0, Style: profitStyle, Label: "Profit"},
+			{Value: 12.0, Style: profitStyle, Label: "More Profit"},
+			{Value: 8.0, Style: profitStyle, Label: "Still Profit"},
+			{Value: -4.0, Style: lossStyle, Label: "Loss!"},
+			{Value: 3.0, Style: profitStyle, Label: "Phew Ok"},
+			{Value: -2.0, Style: lossStyle, Label: "Oh No!"},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	sbc.Render(chart.PNG, f)
+}

examples/basic/main.go

@@ -0,0 +1,23 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+	graph := chart.Chart{
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/benchmark_line_charts/main.go

@@ -0,0 +1,52 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"time"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func random(min, max float64) float64 {
+	return rand.Float64()*(max-min) + min
+}
+
+func main() {
+	numValues := 1024
+	numSeries := 100
+	series := make([]chart.Series, numSeries)
+
+	for i := 0; i < numSeries; i++ {
+		xValues := make([]time.Time, numValues)
+		yValues := make([]float64, numValues)
+
+		for j := 0; j < numValues; j++ {
+			xValues[j] = time.Now().AddDate(0, 0, (numValues-j)*-1)
+			yValues[j] = random(float64(-500), float64(500))
+		}
+
+		series[i] = chart.TimeSeries{
+			Name:    fmt.Sprintf("aaa.bbb.hostname-%v.ccc.ddd.eee.fff.ggg.hhh.iii.jjj.kkk.lll.mmm.nnn.value", i),
+			XValues: xValues,
+			YValues: yValues,
+		}
+	}
+
+	graph := chart.Chart{
+		XAxis: chart.XAxis{
+			Name: "Time",
+		},
+		YAxis: chart.YAxis{
+			Name: "Value",
+		},
+		Series: series,
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/css_classes/main.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+// Note: Additional examples on how to add Stylesheets are in the custom_stylesheets example
+
+func inlineSVGWithClasses(res http.ResponseWriter, req *http.Request) {
+	res.Write([]byte(
+		"<!DOCTYPE html><html><head>" +
+			"<link rel=\"stylesheet\" type=\"text/css\" href=\"/main.css\">" +
+			"</head>" +
+			"<body>"))
+
+	pie := chart.PieChart{
+		// Notes: * Setting ClassName will cause all other inline styles to be dropped!
+		//        * The following type classes may be added additionally: stroke, fill, text
+		Background: chart.Style{ClassName: "background"},
+		Canvas: chart.Style{
+			ClassName: "canvas",
+		},
+		Width:  512,
+		Height: 512,
+		Values: []chart.Value{
+			{Value: 5, Label: "Blue", Style: chart.Style{ClassName: "blue"}},
+			{Value: 5, Label: "Green", Style: chart.Style{ClassName: "green"}},
+			{Value: 4, Label: "Gray", Style: chart.Style{ClassName: "gray"}},
+		},
+	}
+
+	err := pie.Render(chart.SVG, res)
+	if err != nil {
+		fmt.Printf("Error rendering pie chart: %v\n", err)
+	}
+	res.Write([]byte("</body>"))
+}
+
+func css(res http.ResponseWriter, req *http.Request) {
+	res.Header().Set("Content-Type", "text/css")
+	res.Write([]byte("svg .background { fill: white; }" +
+		"svg .canvas { fill: white; }" +
+		"svg .blue.fill.stroke { fill: blue; stroke: lightblue; }" +
+		"svg .green.fill.stroke { fill: green; stroke: lightgreen; }" +
+		"svg .gray.fill.stroke { fill: gray; stroke: lightgray; }" +
+		"svg .blue.text { fill: white; }" +
+		"svg .green.text { fill: white; }" +
+		"svg .gray.text { fill: white; }"))
+}
+
+func main() {
+	http.HandleFunc("/", inlineSVGWithClasses)
+	http.HandleFunc("/main.css", css)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

examples/custom_formatters/main.go

@@ -0,0 +1,38 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+	/*
+	   In this example we use a custom `ValueFormatter` for the y axis, letting us specify how to format text of the y-axis ticks.
+	   You can also do this for the x-axis, or the secondary y-axis.
+	   This example also shows what the chart looks like with the x-axis left off or not shown.
+	*/
+
+	graph := chart.Chart{
+		YAxis: chart.YAxis{
+			ValueFormatter: func(v interface{}) string {
+				if vf, isFloat := v.(float64); isFloat {
+					return fmt.Sprintf("%0.6f", vf)
+				}
+				return ""
+			},
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/custom_padding/main.go

@@ -0,0 +1,34 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+	"github.com/wcharczuk/go-chart/v2/drawing"
+)
+
+func main() {
+	graph := chart.Chart{
+		Background: chart.Style{
+			Padding: chart.Box{
+				Top:    50,
+				Left:   25,
+				Right:  25,
+				Bottom: 10,
+			},
+			FillColor: drawing.ColorFromHex("efefef"),
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: chart.Seq{Sequence: chart.NewLinearSequence().WithStart(1.0).WithEnd(100.0)}.Values(),
+				YValues: chart.Seq{Sequence: chart.NewRandomSequence().WithLen(100).WithMin(100).WithMax(512)}.Values(),
+			},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/custom_ranges/main.go

@@ -0,0 +1,34 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+	/*
+	   In this example we set a custom range for the y-axis, overriding the automatic range generation.
+	   Note: the chart will still generate the ticks automatically based on the custom range, so the intervals may be a bit weird.
+	*/
+
+	graph := chart.Chart{
+		YAxis: chart.YAxis{
+			Range: &chart.ContinuousRange{
+				Min: 0.0,
+				Max: 10.0,
+			},
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/custom_styles/main.go

@@ -0,0 +1,38 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+	"github.com/wcharczuk/go-chart/v2/drawing"
+)
+
+func main() {
+	/*
+	   In this example we set some custom colors for the series and the chart background and canvas.
+	*/
+	graph := chart.Chart{
+		Background: chart.Style{
+			FillColor: drawing.ColorBlue,
+		},
+		Canvas: chart.Style{
+			FillColor: drawing.ColorFromHex("efefef"),
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					StrokeColor: drawing.ColorRed,               // will supercede defaults
+					FillColor:   drawing.ColorRed.WithAlpha(64), // will supercede defaults
+				},
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/custom_stylesheets/inlineOutput.svg

@@ -0,0 +1,21 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="512" height="512">\n<style type="text/css"><![CDATA[svg .background { fill: white; }svg .canvas { fill: white; }svg path.blue { fill: blue; stroke: lightblue; }svg path.green { fill: green; stroke: lightgreen; }svg path.gray { fill: gray; stroke: lightgray; }svg text.blue { fill: white; }svg text.green { fill: white; }svg text.gray { fill: white; }]]></style><path  d="M 0 0
+L 512 0
+L 512 512
+L 0 512
+L 0 0" class="background"/><path  d="M 5 5
+L 507 5
+L 507 507
+L 5 507
+L 5 5" class="canvas"/><path  d="M 256 256
+L 507 256
+A 251 251 128.56 0 1 100 452
+L 256 256
+Z" class="blue"/><path  d="M 256 256
+L 100 452
+A 251 251 128.56 0 1 201 12
+L 256 256
+Z" class="green"/><path  d="M 256 256
+L 201 12
+A 251 251 102.85 0 1 506 256
+L 256 256
+Z" class="gray"/><text x="313" y="413" class="blue">Blue</text><text x="73" y="226" class="green">Green</text><text x="344" y="133" class="gray">Gray</text></svg>

examples/custom_stylesheets/main.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+const style = "svg .background { fill: white; }" +
+	"svg .canvas { fill: white; }" +
+	"svg .blue.fill.stroke { fill: blue; stroke: lightblue; }" +
+	"svg .green.fill.stroke { fill: green; stroke: lightgreen; }" +
+	"svg .gray.fill.stroke { fill: gray; stroke: lightgray; }" +
+	"svg .blue.text { fill: white; }" +
+	"svg .green.text { fill: white; }" +
+	"svg .gray.text { fill: white; }"
+
+func svgWithCustomInlineCSS(res http.ResponseWriter, _ *http.Request) {
+	res.Header().Set("Content-Type", chart.ContentTypeSVG)
+
+	// Render the CSS with custom css
+	err := pieChart().Render(chart.SVGWithCSS(style, ""), res)
+	if err != nil {
+		fmt.Printf("Error rendering pie chart: %v\n", err)
+	}
+}
+
+func svgWithCustomInlineCSSNonce(res http.ResponseWriter, _ *http.Request) {
+	// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/style-src
+	// This should be randomly generated on every request!
+	const nonce = "RAND0MBASE64"
+
+	res.Header().Set("Content-Security-Policy", fmt.Sprintf("style-src 'nonce-%s'", nonce))
+	res.Header().Set("Content-Type", chart.ContentTypeSVG)
+
+	// Render the CSS with custom css and a nonce.
+	// Try changing the nonce to a different string - your browser should block the CSS.
+	err := pieChart().Render(chart.SVGWithCSS(style, nonce), res)
+	if err != nil {
+		fmt.Printf("Error rendering pie chart: %v\n", err)
+	}
+}
+
+func svgWithCustomExternalCSS(res http.ResponseWriter, _ *http.Request) {
+	// Add external CSS
+	res.Write([]byte(
+		`<?xml version="1.0" standalone="no"?>` +
+			`<?xml-stylesheet href="/main.css" type="text/css"?>` +
+			`<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">`))
+
+	res.Header().Set("Content-Type", chart.ContentTypeSVG)
+	err := pieChart().Render(chart.SVG, res)
+	if err != nil {
+		fmt.Printf("Error rendering pie chart: %v\n", err)
+	}
+}
+
+func pieChart() chart.PieChart {
+	return chart.PieChart{
+		// Note that setting ClassName will cause all other inline styles to be dropped!
+		Background: chart.Style{ClassName: "background"},
+		Canvas: chart.Style{
+			ClassName: "canvas",
+		},
+		Width:  512,
+		Height: 512,
+		Values: []chart.Value{
+			{Value: 5, Label: "Blue", Style: chart.Style{ClassName: "blue"}},
+			{Value: 5, Label: "Green", Style: chart.Style{ClassName: "green"}},
+			{Value: 4, Label: "Gray", Style: chart.Style{ClassName: "gray"}},
+		},
+	}
+}
+
+func css(res http.ResponseWriter, req *http.Request) {
+	res.Header().Set("Content-Type", "text/css")
+	res.Write([]byte(style))
+}
+
+func main() {
+	http.HandleFunc("/", svgWithCustomInlineCSS)
+	http.HandleFunc("/nonce", svgWithCustomInlineCSSNonce)
+	http.HandleFunc("/external", svgWithCustomExternalCSS)
+	http.HandleFunc("/main.css", css)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

examples/custom_ticks/main.go

@@ -0,0 +1,42 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+	/*
+	   In this example we set a custom set of ticks to use for the y-axis. It can be (almost) whatever you want, including some custom labels for ticks.
+	   Custom ticks will supercede a custom range, which will supercede automatic generation based on series values.
+	*/
+
+	graph := chart.Chart{
+		YAxis: chart.YAxis{
+			Range: &chart.ContinuousRange{
+				Min: 0.0,
+				Max: 4.0,
+			},
+			Ticks: []chart.Tick{
+				{Value: 0.0, Label: "0.00"},
+				{Value: 2.0, Label: "2.00"},
+				{Value: 4.0, Label: "4.00"},
+				{Value: 6.0, Label: "6.00"},
+				{Value: 8.0, Label: "Eight"},
+				{Value: 10.0, Label: "Ten"},
+			},
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/descending/main.go

@@ -0,0 +1,49 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+
+	/*
+	   The below will draw the same chart as the `basic` example, except with both the x and y axes turned on.
+	   In this case, both the x and y axis ticks are generated automatically, the x and y ranges are established automatically,
+	   the canvas "box" is adjusted to fit the space the axes occupy so as not to clip.
+	   Additionally, it shows how you can use the "Descending" property of continuous ranges to change the ordering of
+	   how values (including ticks) are drawn.
+	*/
+
+	graph := chart.Chart{
+		Height: 500,
+		Width:  500,
+		XAxis:  chart.XAxis{
+			/*Range: &chart.ContinuousRange{
+				Descending: true,
+			},*/
+		},
+		YAxis: chart.YAxis{
+			Range: &chart.ContinuousRange{
+				Descending: true,
+			},
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					StrokeColor: chart.GetDefaultColor(0).WithAlpha(64),
+					FillColor:   chart.GetDefaultColor(0).WithAlpha(64),
+				},
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}

examples/donut_chart/main.go

@@ -0,0 +1,28 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+)
+
+func main() {
+	pie := chart.DonutChart{
+		Width:  512,
+		Height: 512,
+		Values: []chart.Value{
+			{Value: 5, Label: "Blue"},
+			{Value: 5, Label: "Green"},
+			{Value: 4, Label: "Gray"},
+			{Value: 4, Label: "Orange"},
+			{Value: 3, Label: "Deep Blue"},
+			{Value: 3, Label: "test"},
+		},
+	}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	pie.Render(chart.PNG, f)
+}

examples/donut_chart/reg.svg

@@ -0,0 +1,25 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="512" height="512">\n<path  d="M 0 0
+L 512 0
+L 512 512
+L 0 512
+L 0 0" style="stroke-width:0;stroke:rgba(255,255,255,1.0);fill:rgba(255,255,255,1.0)"/><path  d="M 5 5
+L 507 5
+L 507 507
+L 5 507
+L 5 5" style="stroke-width:0;stroke:rgba(255,255,255,1.0);fill:rgba(255,255,255,1.0)"/><path  d="M 256 256
+L 438 256
+A 182 182 225.00 1 1 127 127
+L 256 256
+Z" style="stroke-width:4;stroke:rgba(255,255,255,1.0);fill:rgba(106,195,203,1.0)"/><path  d="M 256 256
+L 127 127
+A 182 182 90.00 0 1 385 127
+L 256 256
+Z" style="stroke-width:4;stroke:rgba(255,255,255,1.0);fill:rgba(42,190,137,1.0)"/><path  d="M 256 256
+L 385 127
+A 182 182 45.00 0 1 438 256
+L 256 256
+Z" style="stroke-width:4;stroke:rgba(255,255,255,1.0);fill:rgba(110,128,139,1.0)"/><path  d="M 256 256
+L 321 256
+A 65 65 359.00 1 1 321 255
+L 256 256
+Z" style="stroke-width:4;stroke:rgba(255,255,255,1.0);fill:rgba(255,255,255,1.0)"/><text x="159" y="461" style="stroke-width:0;stroke:none;fill:rgba(51,51,51,1.0);font-size:15.3px;font-family:'Roboto Medium',sans-serif">Blue</text><text x="241" y="48" style="stroke-width:0;stroke:none;fill:rgba(51,51,51,1.0);font-size:15.3px;font-family:'Roboto Medium',sans-serif">Two</text><text x="440" y="181" style="stroke-width:0;stroke:none;fill:rgba(51,51,51,1.0);font-size:15.3px;font-family:'Roboto Medium',sans-serif">One</text></svg>

examples/horizontal_stacked_bar/main.go

@@ -0,0 +1,222 @@
+package main
+
+import (
+	"os"
+
+	"github.com/wcharczuk/go-chart/v2"
+	"github.com/wcharczuk/go-chart/v2/drawing"
+)
+
+func main() {
+	chart.DefaultBackgroundColor = chart.ColorTransparent
+	chart.DefaultCanvasColor = chart.ColorTransparent
+
+	barWidth := 80
+
+	var (
+		colorWhite          = drawing.Color{R: 241, G: 241, B: 241, A: 255}
+		colorMariner        = drawing.Color{R: 60, G: 100, B: 148, A: 255}
+		colorLightSteelBlue = drawing.Color{R: 182, G: 195, B: 220, A: 255}
+		colorPoloBlue       = drawing.Color{R: 126, G: 155, B: 200, A: 255}
+		colorSteelBlue      = drawing.Color{R: 73, G: 120, B: 177, A: 255}
+	)
+
+	stackedBarChart := chart.StackedBarChart{
+		Title:      "Quarterly Sales",
+		TitleStyle: chart.Shown(),
+		Background: chart.Style{
+			Padding: chart.Box{
+				Top: 75,
+			},
+		},
+		Width:        800,
+		Height:       600,
+		XAxis:        chart.Shown(),
+		YAxis:        chart.Shown(),
+		BarSpacing:   40,
+		IsHorizontal: true,
+		Bars: []chart.StackedBar{
+			{
+				Name:  "Q1",
+				Width: barWidth,
+				Values: []chart.Value{
+					{
+						Label: "32K",
+						Value: 32,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorMariner,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "46K",
+						Value: 46,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorLightSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "48K",
+						Value: 48,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorPoloBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "42K",
+						Value: 42,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+				},
+			},
+			{
+				Name:  "Q2",
+				Width: barWidth,
+				Values: []chart.Value{
+					{
+						Label: "45K",
+						Value: 45,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorMariner,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "60K",
+						Value: 60,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorLightSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "62K",
+						Value: 62,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorPoloBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "53K",
+						Value: 53,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+				},
+			},
+			{
+				Name:  "Q3",
+				Width: barWidth,
+				Values: []chart.Value{
+					{
+						Label: "54K",
+						Value: 54,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorMariner,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "58K",
+						Value: 58,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorLightSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "55K",
+						Value: 55,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorPoloBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "47K",
+						Value: 47,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+				},
+			},
+			{
+				Name:  "Q4",
+				Width: barWidth,
+				Values: []chart.Value{
+					{
+						Label: "46K",
+						Value: 46,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorMariner,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "70K",
+						Value: 70,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorLightSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "74K",
+						Value: 74,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorPoloBlue,
+							FontColor:   colorWhite,
+						},
+					},
+					{
+						Label: "60K",
+						Value: 60,
+						Style: chart.Style{
+							StrokeWidth: .01,
+							FillColor:   colorSteelBlue,
+							FontColor:   colorWhite,
+						},
+					},
+				},
+			},
+		},
+	}
+
+	pngFile, err := os.Create("output.png")
+	if err != nil {
+		panic(err)
+	}
+
+	if err := stackedBarChart.Render(chart.PNG, pngFile); err != nil {
+		panic(err)
+	}
+
+	if err := pngFile.Close(); err != nil {
+		panic(err)
+	}
+}