From d5f8e79c885bdf6c58dfb5b49845bcbf035bd3cb Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Mon, 15 Dec 2014 01:45:41 +0900
Subject: [PATCH] Add RotateHue

---
 colormatrix.go        | 23 ++++++++++++++++++++---
 example/paint/main.go | 14 ++++++++++++--
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/colormatrix.go b/colormatrix.go
index aef7db648..8ee1c7e05 100644
--- a/colormatrix.go
+++ b/colormatrix.go
@@ -68,9 +68,9 @@ func (c *ColorMatrix) setElement(i, j int, element float64) {
 
 // Monochrome returns a color matrix to make an image monochrome.
 func Monochrome() ColorMatrix {
-	const r float64 = 6968.0 / 32768.0
-	const g float64 = 23434.0 / 32768.0
-	const b float64 = 2366.0 / 32768.0
+	const r = 6968.0 / 32768.0
+	const g = 23434.0 / 32768.0
+	const b = 2366.0 / 32768.0
 	return ColorMatrix{
 		[ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{r, g, b, 0, 0},
@@ -81,6 +81,23 @@ func Monochrome() 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{
+		[ColorMatrixDim - 1][ColorMatrixDim]float64{
+			{v1, v2, v3, 0, 0},
+			{v3, v1, v2, 0, 0},
+			{v2, v3, v1, 0, 0},
+			{0, 0, 0, 1, 0},
+		},
+	}
+}
+
 func rgba(clr color.Color) (float64, float64, float64, float64) {
 	r, g, b, a := clr.RGBA()
 	rf := float64(r) / float64(math.MaxUint16)
diff --git a/example/paint/main.go b/example/paint/main.go
index a52f5563d..c9d171563 100644
--- a/example/paint/main.go
+++ b/example/paint/main.go
@@ -4,7 +4,9 @@ import (
 	"fmt"
 	"github.com/hajimehoshi/ebiten"
 	"github.com/hajimehoshi/ebiten/ebitenutil"
+	"image/color"
 	"log"
+	"math"
 	"runtime"
 )
 
@@ -14,11 +16,15 @@ const (
 )
 
 type Game struct {
+	count              int
 	brushRenderTarget  ebiten.RenderTargetID
 	canvasRenderTarget ebiten.RenderTargetID
 }
 
 func (g *Game) Update() error {
+	if ebiten.IsMouseButtonPressed(ebiten.MouseButtonLeft) {
+		g.count++
+	}
 	return nil
 }
 
@@ -31,7 +37,7 @@ func (g *Game) Draw(gr ebiten.GraphicsContext) error {
 		}
 
 		gr.PushRenderTarget(g.brushRenderTarget)
-		gr.Fill(0, 0, 0)
+		gr.Fill(0xff, 0xff, 0xff)
 		gr.PopRenderTarget()
 	}
 	if g.canvasRenderTarget.IsNil() {
@@ -50,7 +56,11 @@ func (g *Game) Draw(gr ebiten.GraphicsContext) error {
 		gr.PushRenderTarget(g.canvasRenderTarget)
 		geo := ebiten.GeometryMatrixI()
 		geo.Translate(float64(mx), float64(my))
-		ebiten.DrawWhole(gr.RenderTarget(g.brushRenderTarget), 1, 1, geo, ebiten.ColorMatrixI())
+		clr := ebiten.ColorMatrixI()
+		clr.Scale(color.RGBA{0xff, 0xff, 0x00, 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)
 		gr.PopRenderTarget()
 	}