diff --git a/example/blocks/game.go b/example/blocks/game.go
index 4edfd3018..317f11081 100644
--- a/example/blocks/game.go
+++ b/example/blocks/game.go
@@ -2,7 +2,6 @@ package blocks
 
 import (
 	"github.com/hajimehoshi/ebiten/graphics"
-	_ "image/png"
 	"sync"
 )
 
diff --git a/example/blocks/textures.go b/example/blocks/textures.go
index eb9b95d69..dd7697a95 100644
--- a/example/blocks/textures.go
+++ b/example/blocks/textures.go
@@ -3,6 +3,7 @@ package blocks
 import (
 	"github.com/hajimehoshi/ebiten/graphics"
 	"image"
+	_ "image/png"
 	"os"
 	"sync"
 )
diff --git a/graphics/opengl/context.go b/graphics/opengl/context.go
index 4fc3ce84c..8ddfc5d3e 100644
--- a/graphics/opengl/context.go
+++ b/graphics/opengl/context.go
@@ -46,7 +46,7 @@ func NewContext(screenWidth, screenHeight, screenScale int) *Context {
 	var err error
 	context.screenId, err = idsInstance.createRenderTarget(screenWidth, screenHeight, graphics.FilterNearest)
 	if err != nil {
-		panic("initializing the offscreen failed: " + err.Error())
+		panic("opengl.NewContext: initializing the offscreen failed: " + err.Error())
 	}
 	context.ResetOffscreen()
 	context.Clear()
diff --git a/graphics/opengl/ids.go b/graphics/opengl/ids.go
index 7fe66ed59..6fb0a5409 100644
--- a/graphics/opengl/ids.go
+++ b/graphics/opengl/ids.go
@@ -10,16 +10,6 @@ import (
 	"sync"
 )
 
-func glMatrix(matrix [4][4]float64) [16]float32 {
-	result := [16]float32{}
-	for j := 0; j < 4; j++ {
-		for i := 0; i < 4; i++ {
-			result[i+j*4] = float32(matrix[i][j])
-		}
-	}
-	return result
-}
-
 type ids struct {
 	textures              map[graphics.TextureID]*Texture
 	renderTargets         map[graphics.RenderTargetID]*RenderTarget
@@ -36,15 +26,11 @@ var idsInstance = &ids{
 	currentRenderTargetId: -1,
 }
 
-func CreateRenderTarget(
-	width, height int,
-	filter graphics.Filter) (graphics.RenderTargetID, error) {
+func CreateRenderTarget(width, height int, filter graphics.Filter) (graphics.RenderTargetID, error) {
 	return idsInstance.createRenderTarget(width, height, filter)
 }
 
-func CreateTexture(
-	img image.Image,
-	filter graphics.Filter) (graphics.TextureID, error) {
+func CreateTexture(img image.Image, filter graphics.Filter) (graphics.TextureID, error) {
 	return idsInstance.createTexture(img, filter)
 }
 
@@ -153,7 +139,7 @@ func (i *ids) drawTexture(
 	r := i.renderTargetAt(target)
 	projectionMatrix := r.projectionMatrix()
 	quads := graphics.TextureQuads(parts, texture.width, texture.height)
-	shader.DrawTexture(texture.native, glMatrix(projectionMatrix), quads, geo, color)
+	shader.DrawTexture(texture.native, projectionMatrix, quads, geo, color)
 }
 
 func (i *ids) setViewportIfNeeded(id graphics.RenderTargetID) {
diff --git a/graphics/opengl/internal/shader/drawtexture.go b/graphics/opengl/internal/shader/drawtexture.go
index 9e0694021..d36989cab 100644
--- a/graphics/opengl/internal/shader/drawtexture.go
+++ b/graphics/opengl/internal/shader/drawtexture.go
@@ -7,9 +7,19 @@ import (
 	"sync"
 )
 
+func glMatrix(matrix [4][4]float64) [16]float32 {
+	result := [16]float32{}
+	for j := 0; j < 4; j++ {
+		for i := 0; i < 4; i++ {
+			result[i+j*4] = float32(matrix[i][j])
+		}
+	}
+	return result
+}
+
 var once sync.Once
 
-func DrawTexture(native gl.Texture, projectionMatrix [16]float32, quads []graphics.TextureQuad, geo matrix.Geometry, color matrix.Color) {
+func DrawTexture(native gl.Texture, projectionMatrix [4][4]float64, quads []graphics.TextureQuad, geo matrix.Geometry, color matrix.Color) {
 	once.Do(func() {
 		initialize()
 	})
@@ -18,7 +28,7 @@ func DrawTexture(native gl.Texture, projectionMatrix [16]float32, quads []graphi
 		return
 	}
 	// TODO: Check performance
-	shaderProgram := use(projectionMatrix, geo, color)
+	shaderProgram := use(glMatrix(projectionMatrix), geo, color)
 
 	native.Bind(gl.TEXTURE_2D)
 	defer gl.Texture(0).Bind(gl.TEXTURE_2D)
diff --git a/ui/glfw/ui.go b/ui/glfw/ui.go
index b73f326f8..e2346f3aa 100644
--- a/ui/glfw/ui.go
+++ b/ui/glfw/ui.go
@@ -19,7 +19,6 @@ type UI struct {
 
 func (u *UI) Start(width, height, scale int, title string) (ui.Canvas, error) {
 	if !glfw.Init() {
-		// TODO: Use glfw error
 		return nil, errors.New("glfw.Init() fails")
 	}
 	glfw.WindowHint(glfw.Resizable, glfw.False)