diff --git a/graphics/matrix/color.go b/graphics/matrix/color.go
index 822819b6b..896df9970 100644
--- a/graphics/matrix/color.go
+++ b/graphics/matrix/color.go
@@ -5,15 +5,15 @@ import (
 	"math"
 )
 
-const colorDim = 5
+const ColorDim = 5
 
 type Color struct {
-	Elements [colorDim - 1][colorDim]float64
+	Elements [ColorDim - 1][ColorDim]float64
 }
 
 func ColorI() Color {
 	return Color{
-		[colorDim - 1][colorDim]float64{
+		[ColorDim - 1][ColorDim]float64{
 			{1, 0, 0, 0, 0},
 			{0, 1, 0, 0, 0},
 			{0, 0, 1, 0, 0},
@@ -23,7 +23,7 @@ func ColorI() Color {
 }
 
 func (matrix *Color) Dim() int {
-	return colorDim
+	return ColorDim
 }
 
 func (matrix *Color) Concat(other Color) {
@@ -49,7 +49,7 @@ func Monochrome() Color {
 	const g float64 = 23434.0 / 32768.0
 	const b float64 = 2366.0 / 32768.0
 	return Color{
-		[colorDim - 1][colorDim]float64{
+		[ColorDim - 1][ColorDim]float64{
 			{r, g, b, 0, 0},
 			{r, g, b, 0, 0},
 			{r, g, b, 0, 0},
diff --git a/graphics/matrix/geometry.go b/graphics/matrix/geometry.go
index bb41e1b47..2274168b9 100644
--- a/graphics/matrix/geometry.go
+++ b/graphics/matrix/geometry.go
@@ -4,15 +4,15 @@ import (
 	"math"
 )
 
-const geometryDim = 3
+const GeometryDim = 3
 
 type Geometry struct {
-	Elements [geometryDim - 1][geometryDim]float64
+	Elements [GeometryDim - 1][GeometryDim]float64
 }
 
 func GeometryI() Geometry {
 	return Geometry{
-		[geometryDim - 1][geometryDim]float64{
+		[GeometryDim - 1][GeometryDim]float64{
 			{1, 0, 0},
 			{0, 1, 0},
 		},
@@ -20,7 +20,7 @@ func GeometryI() Geometry {
 }
 
 func (matrix *Geometry) Dim() int {
-	return geometryDim
+	return GeometryDim
 }
 
 func (matrix *Geometry) Concat(other Geometry) {
diff --git a/ui/glfw/canvas.go b/ui/glfw/canvas.go
index b7c200719..f368a6a53 100644
--- a/ui/glfw/canvas.go
+++ b/ui/glfw/canvas.go
@@ -10,22 +10,22 @@ import (
 	"runtime"
 )
 
-type Canvas struct {
+type canvas struct {
 	window    *glfw.Window
 	context   *opengl.Context
-	keyboard  *Keyboard
+	keyboard  *keyboard
 	funcs     chan func()
 	funcsDone chan struct{}
 }
 
-func NewCanvas(width, height, scale int, title string) *Canvas {
+func newCanvas(width, height, scale int, title string) *canvas {
 	window, err := glfw.CreateWindow(width*scale, height*scale, title, nil, nil)
 	if err != nil {
 		panic(err)
 	}
-	canvas := &Canvas{
+	canvas := &canvas{
 		window:    window,
-		keyboard:  NewKeyboard(),
+		keyboard:  newKeyboard(),
 		funcs:     make(chan func()),
 		funcsDone: make(chan struct{}),
 	}
@@ -44,7 +44,7 @@ func NewCanvas(width, height, scale int, title string) *Canvas {
 	return canvas
 }
 
-func (c *Canvas) Draw(d ui.Drawer) (err error) {
+func (c *canvas) Draw(d ui.Drawer) (err error) {
 	c.use(func() {
 		err = c.context.Update(d)
 		c.window.SwapBuffers()
@@ -52,11 +52,11 @@ func (c *Canvas) Draw(d ui.Drawer) (err error) {
 	return
 }
 
-func (c *Canvas) IsClosed() bool {
+func (c *canvas) IsClosed() bool {
 	return c.window.ShouldClose()
 }
 
-func (c *Canvas) NewTextureID(img image.Image, filter graphics.Filter) (graphics.TextureID, error) {
+func (c *canvas) NewTextureID(img image.Image, filter graphics.Filter) (graphics.TextureID, error) {
 	var id graphics.TextureID
 	var err error
 	c.use(func() {
@@ -65,7 +65,7 @@ func (c *Canvas) NewTextureID(img image.Image, filter graphics.Filter) (graphics
 	return id, err
 }
 
-func (c *Canvas) NewRenderTargetID(width, height int, filter graphics.Filter) (graphics.RenderTargetID, error) {
+func (c *canvas) NewRenderTargetID(width, height int, filter graphics.Filter) (graphics.RenderTargetID, error) {
 	var id graphics.RenderTargetID
 	var err error
 	c.use(func() {
@@ -74,7 +74,7 @@ func (c *Canvas) NewRenderTargetID(width, height int, filter graphics.Filter) (g
 	return id, err
 }
 
-func (c *Canvas) run() {
+func (c *canvas) run() {
 	go func() {
 		runtime.LockOSThread()
 		c.window.MakeContextCurrent()
@@ -87,11 +87,11 @@ func (c *Canvas) run() {
 	}()
 }
 
-func (c *Canvas) use(f func()) {
+func (c *canvas) use(f func()) {
 	c.funcs <- f
 	<-c.funcsDone
 }
 
-func (c *Canvas) update() {
+func (c *canvas) update() {
 	c.keyboard.update(c.window)
 }
diff --git a/ui/glfw/keyboard.go b/ui/glfw/keyboard.go
index 6af6b335c..3e99432e1 100644
--- a/ui/glfw/keyboard.go
+++ b/ui/glfw/keyboard.go
@@ -5,17 +5,17 @@ import (
 	"github.com/hajimehoshi/ebiten/input"
 )
 
-type Keyboard struct {
+type keyboard struct {
 	pressedKeys map[input.Key]struct{}
 }
 
-func NewKeyboard() *Keyboard {
-	return &Keyboard{
+func newKeyboard() *keyboard {
+	return &keyboard{
 		pressedKeys: map[input.Key]struct{}{},
 	}
 }
 
-func (k *Keyboard) IsKeyPressed(key input.Key) bool {
+func (k *keyboard) IsKeyPressed(key input.Key) bool {
 	_, ok := k.pressedKeys[key]
 	return ok
 }
@@ -28,7 +28,7 @@ var glfwKeyCodeToKey = map[glfw.Key]input.Key{
 	glfw.KeyDown:  input.KeyDown,
 }
 
-func (k *Keyboard) update(window *glfw.Window) {
+func (k *keyboard) update(window *glfw.Window) {
 	for g, u := range glfwKeyCodeToKey {
 		if window.GetKey(g) == glfw.Press {
 			k.pressedKeys[u] = struct{}{}
diff --git a/ui/glfw/ui.go b/ui/glfw/ui.go
index e2346f3aa..e9be7063a 100644
--- a/ui/glfw/ui.go
+++ b/ui/glfw/ui.go
@@ -2,19 +2,19 @@ package glfw
 
 import (
 	"errors"
+	"fmt"
 	glfw "github.com/go-gl/glfw3"
 	"github.com/hajimehoshi/ebiten/ui"
-	"log"
 )
 
 func init() {
 	glfw.SetErrorCallback(func(err glfw.ErrorCode, desc string) {
-		log.Fatalf("%v: %v\n", err, desc)
+		panic(fmt.Sprintf("%v: %v\n", err, desc))
 	})
 }
 
 type UI struct {
-	canvas *Canvas
+	canvas *canvas
 }
 
 func (u *UI) Start(width, height, scale int, title string) (ui.Canvas, error) {
@@ -22,7 +22,7 @@ func (u *UI) Start(width, height, scale int, title string) (ui.Canvas, error) {
 		return nil, errors.New("glfw.Init() fails")
 	}
 	glfw.WindowHint(glfw.Resizable, glfw.False)
-	u.canvas = NewCanvas(width, height, scale, title)
+	u.canvas = newCanvas(width, height, scale, title)
 	return u.canvas, nil
 }