Adding upstream version 2.1.2.

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

grid_line.go

@@ -0,0 +1,72 @@
+package chart
+
+// GridLineProvider is a type that provides grid lines.
+type GridLineProvider interface {
+	GetGridLines(ticks []Tick, isVertical bool, majorStyle, minorStyle Style) []GridLine
+}
+
+// GridLine is a line on a graph canvas.
+type GridLine struct {
+	IsMinor bool
+	Style   Style
+	Value   float64
+}
+
+// Major returns if the gridline is a `major` line.
+func (gl GridLine) Major() bool {
+	return !gl.IsMinor
+}
+
+// Minor returns if the gridline is a `minor` line.
+func (gl GridLine) Minor() bool {
+	return gl.IsMinor
+}
+
+// Render renders the gridline
+func (gl GridLine) Render(r Renderer, canvasBox Box, ra Range, isVertical bool, defaults Style) {
+	r.SetStrokeColor(gl.Style.GetStrokeColor(defaults.GetStrokeColor()))
+	r.SetStrokeWidth(gl.Style.GetStrokeWidth(defaults.GetStrokeWidth()))
+	r.SetStrokeDashArray(gl.Style.GetStrokeDashArray(defaults.GetStrokeDashArray()))
+
+	if isVertical {
+		lineLeft := canvasBox.Left + ra.Translate(gl.Value)
+		lineBottom := canvasBox.Bottom
+		lineTop := canvasBox.Top
+
+		r.MoveTo(lineLeft, lineBottom)
+		r.LineTo(lineLeft, lineTop)
+		r.Stroke()
+	} else {
+		lineLeft := canvasBox.Left
+		lineRight := canvasBox.Right
+		lineHeight := canvasBox.Bottom - ra.Translate(gl.Value)
+
+		r.MoveTo(lineLeft, lineHeight)
+		r.LineTo(lineRight, lineHeight)
+		r.Stroke()
+	}
+}
+
+// GenerateGridLines generates grid lines.
+func GenerateGridLines(ticks []Tick, majorStyle, minorStyle Style) []GridLine {
+	var gl []GridLine
+	isMinor := false
+
+	if len(ticks) < 3 {
+		return gl
+	}
+
+	for _, t := range ticks[1 : len(ticks)-1] {
+		s := majorStyle
+		if isMinor {
+			s = minorStyle
+		}
+		gl = append(gl, GridLine{
+			Style:   s,
+			IsMinor: isMinor,
+			Value:   t.Value,
+		})
+		isMinor = !isMinor
+	}
+	return gl
+}