From 3cf449c52c37abec3e62a561d18a337c18c75377 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Mon, 15 Dec 2014 09:37:44 +0900
Subject: [PATCH] Change the algorithm of RotateHue

---
 colormatrix.go                     | 32 ++++++++++++++++++++++--------
 example/blocks/blocks/gamescene.go |  6 ++----
 example/paint/main.go              |  6 ++----
 3 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/colormatrix.go b/colormatrix.go
index 6f450186a..42cf085fc 100644
--- a/colormatrix.go
+++ b/colormatrix.go
@@ -110,18 +110,34 @@ func TranslateColor(clr color.Color) ColorMatrix {
 // RotateHue returns a color matrix to rotate the hue
 func RotateHue(theta float64) ColorMatrix {
 	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
-	// TODO: Need to clamp the values between 0 and 1?
-	return ColorMatrix{
+	// RBG to YIQ
+	c := ColorMatrix{
 		[ColorMatrixDim - 1][ColorMatrixDim]float64{
-			{v1, v2, v3, 0, 0},
-			{v3, v1, v2, 0, 0},
-			{v2, v3, v1, 0, 0},
+			{0.299, 0.587, 0.114, 0, 0},
+			{0.596, -0.275, -0.321, 0, 0},
+			{0.212, -0.523, 0.311, 0, 0},
 			{0, 0, 0, 1, 0},
 		},
 	}
+	// Rotate around the Y axis
+	c.Concat(ColorMatrix{
+		[ColorMatrixDim - 1][ColorMatrixDim]float64{
+			{1, 0, 0, 0, 0},
+			{0, cos, sin, 0, 0},
+			{0, -sin, cos, 0, 0},
+			{0, 0, 0, 1, 0},
+		},
+	})
+	// YIQ to RGB
+	c.Concat(ColorMatrix{
+		[ColorMatrixDim - 1][ColorMatrixDim]float64{
+			{1, 0.956, 0.621, 0, 0},
+			{1, -0.272, -0.647, 0, 0},
+			{1, -1.105, 1.702, 0, 0},
+			{0, 0, 0, 1, 0},
+		},
+	})
+	return c
 }
 
 func rgba(clr color.Color) (float64, float64, float64, float64) {
diff --git a/example/blocks/blocks/gamescene.go b/example/blocks/blocks/gamescene.go
index 2d0609415..f980f4ffa 100644
--- a/example/blocks/blocks/gamescene.go
+++ b/example/blocks/blocks/gamescene.go
@@ -115,11 +115,9 @@ func (s *GameScene) Draw(context ebiten.GraphicsContext, textures *Textures) {
 	context.Fill(0xff, 0xff, 0xff)
 
 	field := textures.GetTexture("empty")
-	geoMat := ebiten.GeometryMatrixI()
-	geoMat.Concat(ebiten.ScaleGeometry(float64(fieldWidth)/float64(emptyWidth), float64(fieldHeight)/float64(emptyHeight)))
+	geoMat := ebiten.ScaleGeometry(float64(fieldWidth)/float64(emptyWidth), float64(fieldHeight)/float64(emptyHeight))
 	geoMat.Concat(ebiten.TranslateGeometry(20, 20)) // TODO: magic number?
-	colorMat := ebiten.ColorMatrixI()
-	colorMat.Concat(ebiten.ScaleColor(color.RGBA{0, 0, 0, 0x80}))
+	colorMat := ebiten.ScaleColor(color.RGBA{0, 0, 0, 0x80})
 	ebiten.DrawWhole(context.Texture(field), emptyWidth, emptyHeight, geoMat, colorMat)
 
 	geoMat = ebiten.GeometryMatrixI()
diff --git a/example/paint/main.go b/example/paint/main.go
index a444f53b6..84d8c70a5 100644
--- a/example/paint/main.go
+++ b/example/paint/main.go
@@ -54,10 +54,8 @@ func (g *Game) Draw(gr ebiten.GraphicsContext) error {
 
 	if ebiten.IsMouseButtonPressed(ebiten.MouseButtonLeft) {
 		gr.PushRenderTarget(g.canvasRenderTarget)
-		geo := ebiten.GeometryMatrixI()
-		geo.Concat(ebiten.TranslateGeometry(float64(mx), float64(my)))
-		clr := ebiten.ColorMatrixI()
-		clr.Concat(ebiten.ScaleColor(color.RGBA{0xff, 0xff, 0x00, 0xff}))
+		geo := ebiten.TranslateGeometry(float64(mx), float64(my))
+		clr := ebiten.ScaleColor(color.RGBA{0xff, 0x40, 0x40, 0xff})
 		theta := 2.0 * math.Pi * float64(g.count%60) / 60.0
 		clr.Concat(ebiten.RotateHue(theta))
 		ebiten.DrawWhole(gr.RenderTarget(g.brushRenderTarget), 1, 1, geo, clr)