diff --git a/graphics/context.go b/graphics/context.go
index 165727591..2ef8f7052 100644
--- a/graphics/context.go
+++ b/graphics/context.go
@@ -4,6 +4,7 @@ import (
 	"github.com/hajimehoshi/ebiten/graphics/matrix"
 )
 
+// A Rect represents a rectangle.
 type Rect struct {
 	X      int
 	Y      int
@@ -11,16 +12,19 @@ type Rect struct {
 	Height int
 }
 
+// A TexturePart represents a part of a texture.
 type TexturePart struct {
 	LocationX int
 	LocationY int
 	Source    Rect
 }
 
+// A Drawer is the interface that draws itself.
 type Drawer interface {
 	Draw(parts []TexturePart, geometryMatrix matrix.Geometry, colorMatrix matrix.Color)
 }
 
+// DrawWhole draws the whole texture.
 func DrawWhole(drawer Drawer, width, height int, geo matrix.Geometry, color matrix.Color) {
 	parts := []TexturePart{
 		{0, 0, Rect{0, 0, width, height}},
@@ -28,6 +32,7 @@ func DrawWhole(drawer Drawer, width, height int, geo matrix.Geometry, color matr
 	drawer.Draw(parts, geo, color)
 }
 
+// A Context is the interface that means a context of rendering.
 type Context interface {
 	Clear()
 	Fill(r, g, b uint8)
diff --git a/graphics/texturefactory.go b/graphics/texturefactory.go
index c8163adf1..1332eafb4 100644
--- a/graphics/texturefactory.go
+++ b/graphics/texturefactory.go
@@ -4,6 +4,8 @@ import (
 	"image"
 )
 
+// Filter represents the type of filter to be used when a texture or a render
+// target is maginified or minified.
 type Filter int
 
 const (
@@ -11,23 +13,30 @@ const (
 	FilterLinear
 )
 
+// TextureID represents an ID of a texture.
 type TextureID int
 
+// RenderTargetID represents an ID of a render target.
 // A render target is essentially same as a texture, but it is assumed that the
 // all alpha of a render target is maximum.
 type RenderTargetID int
 
 var currentTextureFactory TextureFactory
 
+// A TextureFactory is the interface that creates a render target or a texture.
+// This method is for the library and a game developer doesn't have to use this.
 type TextureFactory interface {
 	NewRenderTargetID(width, height int, filter Filter) (RenderTargetID, error)
 	NewTextureID(img image.Image, filter Filter) (TextureID, error)
 }
 
+// SetTextureFactory sets the current texture factory.
+// This method is for the library and a game developer doesn't have to use this.
 func SetTextureFactory(textureFactory TextureFactory) {
 	currentTextureFactory = textureFactory
 }
 
+// NewRenderTargetID returns an ID of a newly created render target.
 func NewRenderTargetID(width, height int, filter Filter) (RenderTargetID, error) {
 	if currentTextureFactory == nil {
 		panic("graphics.NewRenderTarget: currentTextureFactory is not set.")
@@ -35,6 +44,7 @@ func NewRenderTargetID(width, height int, filter Filter) (RenderTargetID, error)
 	return currentTextureFactory.NewRenderTargetID(width, height, filter)
 }
 
+// NewRenderTargetID returns an ID of a newly created texture.
 func NewTextureID(img image.Image, filter Filter) (TextureID, error) {
 	if currentTextureFactory == nil {
 		panic("graphics.NewTexture: currentTextureFactory is not set")