Slide legend over

plotter/heat_test.go

@@ -7,14 +7,17 @@ package plotter
 import (
 	"fmt"
 	"log"
+	"os"
 	"testing"
 
 	"github.com/gonum/matrix/mat64"
 	"github.com/gonum/plot"
 	"github.com/gonum/plot/internal/cmpimg"
 	"github.com/gonum/plot/palette"
+	"github.com/gonum/plot/vg"
 	"github.com/gonum/plot/vg/draw"
 	"github.com/gonum/plot/vg/recorder"
+	"github.com/gonum/plot/vg/vgimg"
 )
 
 type offsetUnitGrid struct {
@@ -61,24 +64,44 @@ func ExampleHeatMap() {
 	p.Add(h)
 
 	// Create a legend.
-	rng := h.Max - h.Min
 	thumbs := PaletteThumbnailers(pal)
 	for i := len(thumbs) - 1; i >= 0; i-- {
 		t := thumbs[i]
-		fmin := float64(i) / float64(len(thumbs))
-		fmax := float64(i+1) / float64(len(thumbs))
-		p.Legend.Add(fmt.Sprintf("%.2g - %.2g", h.Min+fmin*rng, h.Min+fmax*rng), t)
+		if i != 0 && i != len(thumbs)-1 {
+			p.Legend.Add("", t)
+			continue
+		}
+		var val float64
+		switch i {
+		case 0:
+			val = h.Min
+		case len(thumbs) - 1:
+			val = h.Max
+		}
+		p.Legend.Add(fmt.Sprintf("%.2g", val), t)
 	}
+	// This is the width of the legend, experimentally determined.
+	const legendWidth = 1.25 * vg.Centimeter
+	// Slide the legend over so it doesn't overlap the HeatMap.
+	p.Legend.XOffs = legendWidth
 
 	p.X.Padding = 0
 	p.Y.Padding = 0
 	p.X.Max = 1.5
 	p.Y.Max = 1.5
 
-	err = p.Save(250, 200, "testdata/heatMap.png")
+	img := vgimg.New(250, 175)
+	dc := draw.New(img)
+	dc = draw.Crop(dc, 0, -legendWidth, 0, 0) // Make space for the legend.
+	p.Draw(dc)
+	w, err := os.Create("testdata/heatMap.png")
 	if err != nil {
 		log.Panic(err)
 	}
+	png := vgimg.PngCanvas{Canvas: img}
+	if _, err = png.WriteTo(w); err != nil {
+		log.Panic(err)
+	}
 }
 
 func TestHeatMap(t *testing.T) {