diff --git a/ebiten.go b/ebiten.go
index 5fb7720fa..ce2bffa23 100644
--- a/ebiten.go
+++ b/ebiten.go
@@ -29,14 +29,14 @@ const (
 )
 
 type Game interface {
-	ScreenWidth() int
-	ScreenHeight() int
 	Init(tf graphics.TextureFactory)
 	Update(context GameContext)
 	Draw(context graphics.Context)
 }
 
 type GameContext interface {
+	ScreenWidth() int
+	ScreenHeight() int
 	InputState() InputState
 	Terminate()
 }
diff --git a/example/game/blank/blank.go b/example/game/blank/blank.go
index 635c5897c..035a43528 100644
--- a/example/game/blank/blank.go
+++ b/example/game/blank/blank.go
@@ -32,14 +32,6 @@ func New() *Blank {
 	return &Blank{}
 }
 
-func (game *Blank) ScreenWidth() int {
-	return 256
-}
-
-func (game *Blank) ScreenHeight() int {
-	return 240
-}
-
 func (game *Blank) Init(tf graphics.TextureFactory) {
 }
 
diff --git a/example/game/input/input.go b/example/game/input/input.go
index 676536925..0d3e8f245 100644
--- a/example/game/input/input.go
+++ b/example/game/input/input.go
@@ -39,14 +39,6 @@ func New() *Input {
 	return &Input{}
 }
 
-func (game *Input) ScreenWidth() int {
-	return 256
-}
-
-func (game *Input) ScreenHeight() int {
-	return 240
-}
-
 func (game *Input) Init(tf graphics.TextureFactory) {
 	file, err := os.Open("images/text.png")
 	if err != nil {
diff --git a/example/game/monochrome/monochrome.go b/example/game/monochrome/monochrome.go
index 8545e1bc0..4d6d75965 100644
--- a/example/game/monochrome/monochrome.go
+++ b/example/game/monochrome/monochrome.go
@@ -31,26 +31,20 @@ import (
 )
 
 type Monochrome struct {
-	ebitenTexture graphics.Texture
-	ch            chan bool
-	colorMatrix   matrix.Color
+	ebitenTexture  graphics.Texture
+	ch             chan bool
+	colorMatrix    matrix.Color
+	geometryMatrix matrix.Geometry
 }
 
 func New() *Monochrome {
 	return &Monochrome{
-		ch:          make(chan bool),
-		colorMatrix: matrix.IdentityColor(),
+		ch:             make(chan bool),
+		colorMatrix:    matrix.IdentityColor(),
+		geometryMatrix: matrix.IdentityGeometry(),
 	}
 }
 
-func (game *Monochrome) ScreenWidth() int {
-	return 256
-}
-
-func (game *Monochrome) ScreenHeight() int {
-	return 240
-}
-
 func (game *Monochrome) Init(tf graphics.TextureFactory) {
 	file, err := os.Open("images/ebiten.png")
 	if err != nil {
@@ -114,15 +108,16 @@ func (game *Monochrome) update() {
 func (game *Monochrome) Update(context ebiten.GameContext) {
 	game.ch <- true
 	<-game.ch
+
+	game.geometryMatrix = matrix.IdentityGeometry()
+	tx := context.ScreenWidth()/2 - game.ebitenTexture.Width()/2
+	ty := context.ScreenHeight()/2 - game.ebitenTexture.Height()/2
+	game.geometryMatrix.Translate(float64(tx), float64(ty))
 }
 
 func (game *Monochrome) Draw(g graphics.Context) {
 	g.Fill(&color.RGBA{R: 128, G: 128, B: 255, A: 255})
 
-	geometryMatrix := matrix.IdentityGeometry()
-	tx := game.ScreenWidth()/2 - game.ebitenTexture.Width()/2
-	ty := game.ScreenHeight()/2 - game.ebitenTexture.Height()/2
-	geometryMatrix.Translate(float64(tx), float64(ty))
 	g.DrawTexture(game.ebitenTexture.ID(),
-		geometryMatrix, game.colorMatrix)
+		game.geometryMatrix, game.colorMatrix)
 }
diff --git a/example/game/rects/rects.go b/example/game/rects/rects.go
index 1d5625d96..3b574a3e7 100644
--- a/example/game/rects/rects.go
+++ b/example/game/rects/rects.go
@@ -31,44 +31,38 @@ import (
 
 type Rects struct {
 	rectsTexture graphics.Texture
+	rect         *graphics.Rect
+	rectColor    *color.RGBA
 }
 
 func New() *Rects {
-	return &Rects{}
-}
-
-func (game *Rects) ScreenWidth() int {
-	return 256
-}
-
-func (game *Rects) ScreenHeight() int {
-	return 240
+	return &Rects{
+		rect:      &graphics.Rect{},
+		rectColor: &color.RGBA{},
+	}
 }
 
 func (game *Rects) Init(tf graphics.TextureFactory) {
-	game.rectsTexture = tf.NewTexture(game.ScreenWidth(), game.ScreenHeight())
+	// TODO: fix
+	game.rectsTexture = tf.NewTexture(256, 240)
 }
 
 func (game *Rects) Update(context ebiten.GameContext) {
+	game.rect.X = rand.Intn(context.ScreenWidth())
+	game.rect.Y = rand.Intn(context.ScreenHeight())
+	game.rect.Width = rand.Intn(context.ScreenWidth() - game.rect.X)
+	game.rect.Height = rand.Intn(context.ScreenHeight() - game.rect.Y)
+
+	game.rectColor.R = uint8(rand.Intn(256))
+	game.rectColor.G = uint8(rand.Intn(256))
+	game.rectColor.B = uint8(rand.Intn(256))
+	game.rectColor.A = uint8(rand.Intn(256))
 }
 
 func (game *Rects) Draw(g graphics.Context) {
 	g.SetOffscreen(game.rectsTexture.ID())
 
-	x := rand.Intn(game.ScreenWidth())
-	y := rand.Intn(game.ScreenHeight())
-	width := rand.Intn(game.ScreenWidth() - x)
-	height := rand.Intn(game.ScreenHeight() - y)
-
-	red := uint8(rand.Intn(256))
-	green := uint8(rand.Intn(256))
-	blue := uint8(rand.Intn(256))
-	alpha := uint8(rand.Intn(256))
-
-	g.DrawRect(
-		graphics.Rect{x, y, width, height},
-		&color.RGBA{red, green, blue, alpha},
-	)
+	g.DrawRect(*game.rect, game.rectColor)
 
 	g.SetOffscreen(g.Screen().ID())
 	g.DrawTexture(game.rectsTexture.ID(),
diff --git a/example/game/rotating/rotating.go b/example/game/rotating/rotating.go
index dd1b9ae50..917767ef0 100644
--- a/example/game/rotating/rotating.go
+++ b/example/game/rotating/rotating.go
@@ -32,22 +32,15 @@ import (
 )
 
 type Rotating struct {
-	ebitenTexture graphics.Texture
-	x             int
+	ebitenTexture  graphics.Texture
+	x              int
+	geometryMatrix matrix.Geometry
 }
 
 func New() *Rotating {
 	return &Rotating{}
 }
 
-func (game *Rotating) ScreenWidth() int {
-	return 256
-}
-
-func (game *Rotating) ScreenHeight() int {
-	return 240
-}
-
 func (game *Rotating) Init(tf graphics.TextureFactory) {
 	file, err := os.Open("images/ebiten.png")
 	if err != nil {
@@ -66,21 +59,20 @@ func (game *Rotating) Init(tf graphics.TextureFactory) {
 
 func (game *Rotating) Update(context ebiten.GameContext) {
 	game.x++
+
+	game.geometryMatrix = matrix.IdentityGeometry()
+	tx, ty := float64(game.ebitenTexture.Width()), float64(game.ebitenTexture.Height())
+	game.geometryMatrix.Translate(-tx/2, -ty/2)
+	game.geometryMatrix.Rotate(float64(game.x) * 2 * math.Pi / float64(ebiten.FPS*10))
+	game.geometryMatrix.Translate(tx/2, ty/2)
+	centerX := float64(context.ScreenWidth()) / 2
+	centerY := float64(context.ScreenHeight()) / 2
+	game.geometryMatrix.Translate(centerX-tx/2, centerY-ty/2)
 }
 
 func (game *Rotating) Draw(g graphics.Context) {
 	g.Fill(&color.RGBA{R: 128, G: 128, B: 255, A: 255})
-
-	geometryMatrix := matrix.IdentityGeometry()
-	tx, ty := float64(game.ebitenTexture.Width()), float64(game.ebitenTexture.Height())
-	geometryMatrix.Translate(-tx/2, -ty/2)
-	geometryMatrix.Rotate(float64(game.x) * 2 * math.Pi / float64(ebiten.FPS*10))
-	geometryMatrix.Translate(tx/2, ty/2)
-	centerX := float64(game.ScreenWidth()) / 2
-	centerY := float64(game.ScreenHeight()) / 2
-	geometryMatrix.Translate(centerX-tx/2, centerY-ty/2)
-
 	g.DrawTexture(game.ebitenTexture.ID(),
-		geometryMatrix,
+		game.geometryMatrix,
 		matrix.IdentityColor())
 }
diff --git a/example/game/sprites/sprites.go b/example/game/sprites/sprites.go
index 35e2c5c76..2dcdc3fa3 100644
--- a/example/game/sprites/sprites.go
+++ b/example/game/sprites/sprites.go
@@ -88,14 +88,6 @@ func New() *Sprites {
 	return &Sprites{}
 }
 
-func (game *Sprites) ScreenWidth() int {
-	return 256
-}
-
-func (game *Sprites) ScreenHeight() int {
-	return 240
-}
-
 func (game *Sprites) Init(tf graphics.TextureFactory) {
 	file, err := os.Open("images/ebiten.png")
 	if err != nil {
@@ -112,9 +104,10 @@ func (game *Sprites) Init(tf graphics.TextureFactory) {
 	}
 	game.sprites = []*Sprite{}
 	for i := 0; i < 100; i++ {
+		// TODO: fix
 		sprite := newSprite(
-			game.ScreenWidth(),
-			game.ScreenHeight(),
+			256,
+			240,
 			game.ebitenTexture.Width(),
 			game.ebitenTexture.Height())
 		game.sprites = append(game.sprites, sprite)
diff --git a/example/game/terminate/terminate.go b/example/game/terminate/terminate.go
index 4773afd87..29371bb9a 100644
--- a/example/game/terminate/terminate.go
+++ b/example/game/terminate/terminate.go
@@ -33,14 +33,6 @@ func New() *Terminate {
 	return &Terminate{60}
 }
 
-func (game *Terminate) ScreenWidth() int {
-	return 256
-}
-
-func (game *Terminate) ScreenHeight() int {
-	return 240
-}
-
 func (game *Terminate) Init(tf graphics.TextureFactory) {
 }
 
diff --git a/example/main.go b/example/main.go
index bd039e61d..f145cc047 100644
--- a/example/main.go
+++ b/example/main.go
@@ -63,5 +63,5 @@ func main() {
 	}
 
 	const screenScale = 2
-	glut.Run(game, screenScale, "Ebiten Demo")
+	glut.Run(game, 256, 240, screenScale, "Ebiten Demo")
 }
diff --git a/graphics/opengl/context.go b/graphics/opengl/context.go
index ab4e86f9c..20558c286 100644
--- a/graphics/opengl/context.go
+++ b/graphics/opengl/context.go
@@ -42,12 +42,9 @@ type Context struct {
 	screenScale            int
 	textures               map[graphics.TextureID]*Texture
 	currentOffscreen       *Texture
-	projectionMatrix       [16]float32
-	currentShaderProgram   C.GLuint
 	mainFramebufferTexture *Texture
 }
 
-// This method should be called on the UI thread.
 func newContext(screenWidth, screenHeight, screenScale int) *Context {
 	context := &Context{
 		screenWidth:  screenWidth,
@@ -126,7 +123,6 @@ func (context *Context) DrawRect(rect graphics.Rect, clr color.Color) {
 	}
 
 	C.glUseProgram(0)
-	context.currentShaderProgram = 0
 	C.glDisable(C.GL_TEXTURE_2D)
 	C.glEnableClientState(C.GL_VERTEX_ARRAY)
 	C.glEnableClientState(C.GL_COLOR_ARRAY)
@@ -161,11 +157,11 @@ func (context *Context) DrawTextureParts(
 		panic("invalid texture ID")
 	}
 
-	context.setShaderProgram(geometryMatrix, colorMatrix)
+	shaderProgram := context.setShaderProgram(geometryMatrix, colorMatrix)
 	C.glBindTexture(C.GL_TEXTURE_2D, texture.id)
 
-	vertexAttrLocation := getAttributeLocation(context.currentShaderProgram, "vertex")
-	textureAttrLocation := getAttributeLocation(context.currentShaderProgram, "texture")
+	vertexAttrLocation := getAttributeLocation(shaderProgram, "vertex")
+	textureAttrLocation := getAttributeLocation(shaderProgram, "texture")
 
 	C.glEnableClientState(C.GL_VERTEX_ARRAY)
 	C.glEnableClientState(C.GL_TEXTURE_COORD_ARRAY)
@@ -220,10 +216,11 @@ func (context *Context) SetOffscreen(textureID graphics.TextureID) {
 		texture.framebuffer = createFramebuffer(texture.id)
 	}
 	context.setOffscreen(texture)
-	context.currentOffscreen = texture
 }
 
 func (context *Context) setOffscreen(texture *Texture) {
+	context.currentOffscreen = texture
+
 	C.glFlush()
 
 	C.glBindFramebuffer(C.GL_FRAMEBUFFER, texture.framebuffer)
@@ -235,6 +232,18 @@ func (context *Context) setOffscreen(texture *Texture) {
 
 	C.glViewport(0, 0, C.GLsizei(abs(texture.textureWidth)),
 		C.GLsizei(abs(texture.textureHeight)))
+}
+
+func (context *Context) resetOffscreen() {
+	context.setOffscreen(context.mainFramebufferTexture)
+}
+
+func (context *Context) flush() {
+	C.glFlush()
+}
+
+func (context *Context) projectionMatrix() [16]float32 {
+	texture := context.currentOffscreen
 
 	var e11, e22, e41, e42 float32
 	if texture != context.mainFramebufferTexture {
@@ -250,7 +259,7 @@ func (context *Context) setOffscreen(texture *Texture) {
 		e42 = -1 + height/float32(texture.textureHeight)*2
 	}
 
-	context.projectionMatrix = [...]float32{
+	return [...]float32{
 		e11, 0, 0, 0,
 		0, e22, 0, 0,
 		0, 0, 1, 0,
@@ -258,20 +267,8 @@ func (context *Context) setOffscreen(texture *Texture) {
 	}
 }
 
-func (context *Context) resetOffscreen() {
-	context.setOffscreen(context.mainFramebufferTexture)
-	context.currentOffscreen = context.mainFramebufferTexture
-}
-
-// This method should be called on the UI thread.
-func (context *Context) flush() {
-	C.glFlush()
-}
-
-// This method should be called on the UI thread.
 func (context *Context) setShaderProgram(
-	geometryMatrix matrix.Geometry, colorMatrix matrix.Color) {
-	program := C.GLuint(0)
+	geometryMatrix matrix.Geometry, colorMatrix matrix.Color) (program C.GLuint) {
 	if colorMatrix.IsIdentity() {
 		program = regularShaderProgram
 	} else {
@@ -279,11 +276,11 @@ func (context *Context) setShaderProgram(
 	}
 	// TODO: cache and skip?
 	C.glUseProgram(program)
-	context.currentShaderProgram = program
 
+	projectionMatrix := context.projectionMatrix()
 	C.glUniformMatrix4fv(getUniformLocation(program, "projection_matrix"),
 		1, C.GL_FALSE,
-		(*C.GLfloat)(&context.projectionMatrix[0]))
+		(*C.GLfloat)(&projectionMatrix[0]))
 
 	a := float32(geometryMatrix.Elements[0][0])
 	b := float32(geometryMatrix.Elements[0][1])
@@ -328,6 +325,8 @@ func (context *Context) setShaderProgram(
 	}
 	C.glUniform4fv(getUniformLocation(program, "color_matrix_translation"),
 		1, (*C.GLfloat)(&glColorMatrixTranslation[0]))
+
+	return
 }
 
 func createFramebuffer(textureID C.GLuint) C.GLuint {
diff --git a/ui/glut/glut.go b/ui/glut/glut.go
index cd5b62631..075cd7972 100644
--- a/ui/glut/glut.go
+++ b/ui/glut/glut.go
@@ -135,10 +135,7 @@ func new(screenWidth, screenHeight, screenScale int, title string) *GlutUI {
 	return ui
 }
 
-func Run(game ebiten.Game, screenScale int, title string) {
-	screenWidth := game.ScreenWidth()
-	screenHeight := game.ScreenHeight()
-
+func Run(game ebiten.Game, screenWidth, screenHeight, screenScale int, title string) {
 	ui := new(screenWidth, screenHeight, screenScale, title)
 	currentUI = ui
 
@@ -175,7 +172,9 @@ func Run(game ebiten.Game, screenScale int, title string) {
 			int64(time.Second) / int64(ebiten.FPS))
 		tick := time.Tick(frameTime)
 		gameContext := &GameContext{
-			inputState: ebiten.InputState{-1, -1},
+			screenWidth:  screenWidth,
+			screenHeight: screenHeight,
+			inputState:   ebiten.InputState{-1, -1},
 		}
 		for {
 			select {
@@ -196,8 +195,18 @@ func Run(game ebiten.Game, screenScale int, title string) {
 }
 
 type GameContext struct {
-	inputState ebiten.InputState
-	terminated bool
+	screenWidth  int
+	screenHeight int
+	inputState   ebiten.InputState
+	terminated   bool
+}
+
+func (context *GameContext) ScreenWidth() int {
+	return context.screenWidth
+}
+
+func (context *GameContext) ScreenHeight() int {
+	return context.screenHeight
 }
 
 func (context *GameContext) InputState() ebiten.InputState {