Add thumbnailer for palette.Palette

plotter/heat_test.go

@@ -5,6 +5,7 @@
 package plotter
 
 import (
+	"fmt"
 	"log"
 	"testing"
 
@@ -48,7 +49,8 @@ func ExampleHeatMap() {
 			5, 6, 7, 8,
 			9, 10, 11, 12,
 		})}
-	h := NewHeatMap(m, palette.Heat(12, 1))
+	plte := palette.Heat(12, 1)
+	h := NewHeatMap(m, plte)
 
 	p, err := plot.New()
 	if err != nil {
@@ -58,6 +60,16 @@ func ExampleHeatMap() {
 
 	p.Add(h)
 
+	// Create a legend.
+	rng := h.Max - h.Min
+	thumbs := PaletteThumbnailers(plte)
+	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)
+	}
+
 	p.X.Padding = 0
 	p.Y.Padding = 0
 	p.X.Max = 1.5