Adding upstream version 2.1.2.

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

image_writer.go

@@ -0,0 +1,42 @@
+package chart
+
+import (
+	"bytes"
+	"errors"
+	"image"
+	"image/png"
+)
+
+// RGBACollector is a render target for a chart.
+type RGBACollector interface {
+	SetRGBA(i *image.RGBA)
+}
+
+// ImageWriter is a special type of io.Writer that produces a final image.
+type ImageWriter struct {
+	rgba     *image.RGBA
+	contents *bytes.Buffer
+}
+
+func (ir *ImageWriter) Write(buffer []byte) (int, error) {
+	if ir.contents == nil {
+		ir.contents = bytes.NewBuffer([]byte{})
+	}
+	return ir.contents.Write(buffer)
+}
+
+// SetRGBA sets a raw version of the image.
+func (ir *ImageWriter) SetRGBA(i *image.RGBA) {
+	ir.rgba = i
+}
+
+// Image returns an *image.Image for the result.
+func (ir *ImageWriter) Image() (image.Image, error) {
+	if ir.rgba != nil {
+		return ir.rgba, nil
+	}
+	if ir.contents != nil && ir.contents.Len() > 0 {
+		return png.Decode(ir.contents)
+	}
+	return nil, errors.New("no valid sources for image data, cannot continue")
+}