image: Deprecate RotateHue

colorm.go

@@ -101,6 +101,23 @@ func (c *ColorM) Translate(r, g, b, a float64) {
 	c.es[3][4] += a
 }
 
+// RotateHue rotates the hue.
+func (c *ColorM) RotateHue(theta float64) {
+	sin, cos := math.Sincos(theta)
+	v1 := cos + (1.0-cos)/3.0
+	v2 := (1.0/3.0)*(1.0-cos) - math.Sqrt(1.0/3.0)*sin
+	v3 := (1.0/3.0)*(1.0-cos) + math.Sqrt(1.0/3.0)*sin
+	c.Concat(ColorM{
+		initialized: true,
+		es: [ColorMDim - 1][ColorMDim]float64{
+			{v1, v2, v3, 0, 0},
+			{v3, v1, v2, 0, 0},
+			{v2, v3, v1, 0, 0},
+			{0, 0, 0, 1, 0},
+		},
+	})
+}
+
 // SetElement sets an element at (i, j).
 func (c *ColorM) SetElement(i, j int, element float64) {
 	if !c.initialized {
@@ -151,7 +168,7 @@ func TranslateColor(r, g, b, a float64) ColorM {
 	}
 }
 
-// RotateHue returns a color matrix to rotate the hue
+// Deprecated as of 1.2.0-alpha. Use RotateHue member function instead.
 func RotateHue(theta float64) ColorM {
 	sin, cos := math.Sincos(theta)
 	v1 := cos + (1.0-cos)/3.0

example/hue/main.go

@@ -37,7 +37,7 @@ func update(screen *ebiten.Image) error {
 	w, h := gophersImage.Size()
 	op := &ebiten.DrawImageOptions{}
 	op.GeoM.Translate(float64(screenWidth-w)/2, float64(screenHeight-h)/2)
-	op.ColorM.Concat(ebiten.RotateHue(float64(count%360) * 2 * math.Pi / 360))
+	op.ColorM.RotateHue(float64(count%360) * 2 * math.Pi / 360)
 	if err := screen.DrawImage(gophersImage, op); err != nil {
 		return err
 	}

example/paint/main.go

@@ -47,7 +47,7 @@ func update(screen *ebiten.Image) error {
 		op.GeoM.Translate(float64(mx), float64(my))
 		op.ColorM.Scale(1.0, 0.25, 0.25, 1.0)
 		theta := 2.0 * math.Pi * float64(count%60) / 60.0
-		op.ColorM.Concat(ebiten.RotateHue(theta))
+		op.ColorM.RotateHue(theta)
 		if err := canvasImage.DrawImage(brushImage, op); err != nil {
 			return err
 		}