plotter: add special handling for image.Uniform

Fixes #752.

Signed-off-by: Sebastien Binet <binet@cern.ch>

Author: sbinet

plotter/image.go

@@ -27,6 +27,12 @@ type Image struct {
 // (xmin, ymin) and (xmax, ymax) points given in the data space.
 // The img will be scaled to fit inside the rectangle.
 func NewImage(img image.Image, xmin, ymin, xmax, ymax float64) *Image {
+	if src, ok := img.(*image.Uniform); ok {
+		img = uniform{
+			src,
+			image.Rect(0, 0, int(xmax-xmin+0.5), int(ymax-ymin+0.5)),
+		}
+	}
 	bounds := img.Bounds()
 	cols := bounds.Dx()
 	rows := bounds.Dy()
@@ -126,3 +132,13 @@ func (img *Image) y(r int) float64 {
 	}
 	return img.ymin + float64(r)*img.dy
 }
+
+// uniform is a cropped uniform image.
+type uniform struct {
+	*image.Uniform
+	rect image.Rectangle
+}
+
+func (img uniform) Bounds() image.Rectangle {
+	return img.rect
+}

plotter/image_example_test.go

@@ -5,6 +5,8 @@
 package plotter_test
 
 import (
+	"image"
+	"image/color"
 	"image/png"
 	"log"
 	"os"
@@ -79,3 +81,22 @@ func ExampleImage_log() {
 		log.Fatalf("error saving image plot: %v\n", err)
 	}
 }
+
+// An example of embedding a uniform image in a plot.
+func ExampleImage_uniform() {
+	p := plot.New()
+	p.Title.Text = "Uniform image"
+
+	img := image.NewUniform(color.RGBA{R: 90, G: 155, B: 212, A: 255})
+	p.Add(plotter.NewImage(img, 100, 100, 10000, 10000))
+
+	const (
+		w = 5 * vg.Centimeter
+		h = 5 * vg.Centimeter
+	)
+
+	err := p.Save(w, h, "testdata/image_plot_uniform.png")
+	if err != nil {
+		log.Fatalf("error saving image plot: %v\n", err)
+	}
+}

plotter/image_test.go

@@ -17,3 +17,7 @@ func TestImagePlot(t *testing.T) {
 func TestImagePlot_log(t *testing.T) {
 	cmpimg.CheckPlot(ExampleImage_log, t, "image_plot_log.png")
 }
+
+func TestImagePlot_uniform(t *testing.T) {
+	cmpimg.CheckPlot(ExampleImage_uniform, t, "image_plot_uniform.png")
+}