From bc91c2210b70d172beea3a61a627034fba22b007 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@hajimehoshi.com>
Date: Thu, 20 Jun 2013 00:49:44 +0900
Subject: [PATCH] Add RotateMatrix and TranslateMatrix

---
 examples/glut/main.go       | 10 +++++++---
 graphics/color_matrix.go    |  4 ++++
 graphics/geometry_matrix.go | 25 +++++++++++++++++++++++++
 3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/examples/glut/main.go b/examples/glut/main.go
index 3c91f8981..3dac9f988 100644
--- a/examples/glut/main.go
+++ b/examples/glut/main.go
@@ -117,10 +117,13 @@ func (game *DemoGame) Update() {
 func (game *DemoGame) Draw(g graphics.GraphicsContext, offscreen graphics.TextureID) {
 	g.Fill(&color.RGBA{R: 128, G: 128, B: 255, A: 255})
 	geometryMatrix := graphics.IdentityGeometryMatrix()
-	geometryMatrix.SetTx(float64(game.x))
-	geometryMatrix.SetTy(float64(game.x))
+	tx, ty := float64(game.ebitenTexture.Width), float64(game.ebitenTexture.Height)
+	geometryMatrix = geometryMatrix.Concat(graphics.TranslateMatrix(-tx/2, -ty/2))
+	geometryMatrix = geometryMatrix.Concat(graphics.RotateMatrix(float64(game.x) / 60))
+	geometryMatrix = geometryMatrix.Concat(graphics.TranslateMatrix(tx/2, ty/2))
+	geometryMatrix = geometryMatrix.Concat(graphics.TranslateMatrix(100, 100))
 	g.DrawTexture(game.ebitenTexture.ID,
-		0, 0, game.ebitenTexture.Width, game.ebitenTexture.Height,
+		0, 0, int(tx), int(ty),
 		geometryMatrix,
 		graphics.IdentityColorMatrix())
 }
@@ -133,4 +136,5 @@ func main() {
 	currentUI.Init()
 
 	ebiten.OpenGLRun(game, currentUI)
+
 }
diff --git a/graphics/color_matrix.go b/graphics/color_matrix.go
index 6a31977a6..7ddd1513f 100644
--- a/graphics/color_matrix.go
+++ b/graphics/color_matrix.go
@@ -14,6 +14,10 @@ func IdentityColorMatrix() *ColorMatrix {
 	return &ColorMatrix{*IdentityAffineMatrix(colorMatrixDimension)}
 }
 
+func (matrix *ColorMatrix) Concat(other *ColorMatrix) *ColorMatrix {
+	return &ColorMatrix{*matrix.AffineMatrix.Concat(&other.AffineMatrix)}
+}
+
 func (matrix *ColorMatrix) Clone() *ColorMatrix {
 	return &ColorMatrix{*(matrix.AffineMatrix.Clone())}
 }
diff --git a/graphics/geometry_matrix.go b/graphics/geometry_matrix.go
index fbe0381a2..60f61ed22 100644
--- a/graphics/geometry_matrix.go
+++ b/graphics/geometry_matrix.go
@@ -1,5 +1,9 @@
 package graphics
 
+import (
+	"math"
+)
+
 type GeometryMatrix struct {
 	AffineMatrix
 }
@@ -14,6 +18,27 @@ func IdentityGeometryMatrix() *GeometryMatrix {
 	return &GeometryMatrix{*IdentityAffineMatrix(geometryMatrixDimension)}
 }
 
+func TranslateMatrix(tx, ty float64) *GeometryMatrix {
+	matrix := IdentityGeometryMatrix()
+	matrix.SetTx(tx)
+	matrix.SetTy(ty)
+	return matrix
+}
+
+func RotateMatrix(theta float64) *GeometryMatrix {
+	matrix := NewGeometryMatrix()
+	cos, sin := math.Cos(theta), math.Sin(theta)
+	matrix.SetA(cos)
+	matrix.SetB(-sin)
+	matrix.SetC(sin)
+	matrix.SetD(cos)
+	return matrix
+}
+
+func (matrix *GeometryMatrix) Concat(other *GeometryMatrix) *GeometryMatrix {
+	return &GeometryMatrix{*matrix.AffineMatrix.Concat(&other.AffineMatrix)}
+}
+
 func (matrix *GeometryMatrix) Clone() *GeometryMatrix {
 	return &GeometryMatrix{*(matrix.AffineMatrix.Clone())}
 }