ebiten: Add BenchmarkColorMScale

Updates #1658

image_test.go

@@ -22,8 +22,10 @@ import (
 	"image/draw"
 	_ "image/png"
 	"math"
+	"math/rand"
 	"runtime"
 	"testing"
+	"time"
 
 	. "github.com/hajimehoshi/ebiten/v2"
 	"github.com/hajimehoshi/ebiten/v2/examples/resources/images"
@@ -31,6 +33,10 @@ import (
 	t "github.com/hajimehoshi/ebiten/v2/internal/testing"
 )
 
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
 func skipTooSlowTests(t *testing.T) bool {
 	if testing.Short() {
 		t.Skip("skipping test in short mode")
@@ -2405,3 +2411,15 @@ func TestImageEvenOdd(t *testing.T) {
 		}
 	}
 }
+
+// #1658
+func BenchmarkColorMScale(b *testing.B) {
+	r := rand.Float64
+	dst := NewImage(16, 16)
+	src := NewImage(16, 16)
+	for n := 0; n < b.N; n++ {
+		op := &DrawImageOptions{}
+		op.ColorM.Scale(r(), r(), r(), r())
+		dst.DrawImage(src, op)
+	}
+}