diff --git a/audio/vorbis/decode.go b/audio/vorbis/decode.go
index a491c8e80..437d03851 100644
--- a/audio/vorbis/decode.go
+++ b/audio/vorbis/decode.go
@@ -27,6 +27,7 @@ import (
 	"github.com/jfreymuth/go-vorbis/ogg/vorbis"
 )
 
+// Stream is a decoded audio stream.
 type Stream struct {
 	buf *bytes.Reader
 }
@@ -60,14 +61,17 @@ func newStream(v *vorbis.Vorbis) (*Stream, error) {
 	return s, nil
 }
 
+// Read is implementation of io.Reader's Read.
 func (s *Stream) Read(p []byte) (int, error) {
 	return s.buf.Read(p)
 }
 
+// Seek is implementation of io.Seeker's Seek.
 func (s *Stream) Seek(offset int64, whence int) (int64, error) {
 	return s.buf.Seek(offset, whence)
 }
 
+// Read is implementation of io.Closer's Close.
 func (s *Stream) Close() error {
 	s.buf = nil
 	return nil
diff --git a/audio/wav/decode.go b/audio/wav/decode.go
index 33b6f492e..a16704ef4 100644
--- a/audio/wav/decode.go
+++ b/audio/wav/decode.go
@@ -23,16 +23,19 @@ import (
 	"github.com/hajimehoshi/ebiten/audio"
 )
 
+// Stream is a decoded audio stream.
 type Stream struct {
 	src        audio.ReadSeekCloser
 	headerSize int64
 	dataSize   int64
 }
 
+// Read is implementation of io.Reader's Read.
 func (s *Stream) Read(p []byte) (int, error) {
 	return s.src.Read(p)
 }
 
+// Seek is implementation of io.Seeker's Seek.
 func (s *Stream) Seek(offset int64, whence int) (int64, error) {
 	if whence == 0 {
 		offset += s.headerSize
@@ -40,6 +43,7 @@ func (s *Stream) Seek(offset int64, whence int) (int64, error) {
 	return s.src.Seek(offset, whence)
 }
 
+// Read is implementation of io.Closer's Close.
 func (s *Stream) Close() error {
 	return s.src.Close()
 }
diff --git a/ebitenutil/debugprint.go b/ebitenutil/debugprint.go
index 39926079c..efb2eb565 100644
--- a/ebitenutil/debugprint.go
+++ b/ebitenutil/debugprint.go
@@ -59,8 +59,9 @@ type debugPrintState struct {
 
 var defaultDebugPrintState = &debugPrintState{}
 
-func DebugPrint(r *ebiten.Image, str string) error {
-	return defaultDebugPrintState.DebugPrint(r, str)
+// DebugPrint draws the string str on the image.
+func DebugPrint(image *ebiten.Image, str string) error {
+	return defaultDebugPrintState.DebugPrint(image, str)
 }
 
 func (d *debugPrintState) drawText(rt *ebiten.Image, str string, x, y int, c color.Color) {
diff --git a/ebitenutil/io.go b/ebitenutil/io.go
index 4e5c23f67..9f5197123 100644
--- a/ebitenutil/io.go
+++ b/ebitenutil/io.go
@@ -18,6 +18,7 @@ import (
 	"io"
 )
 
+// ReadSeekCloser is io.ReadSeeker and io.Closer.
 type ReadSeekCloser interface {
 	io.ReadSeeker
 	io.Closer
diff --git a/graphics.go b/graphics.go
index 19fe241b7..f357340ad 100644
--- a/graphics.go
+++ b/graphics.go
@@ -22,8 +22,11 @@ import (
 type Filter int
 
 const (
-	FilterNearest Filter = iota // nearest (crisp-edged) filter
-	FilterLinear                // linear filter
+	// FilterNearest represents nearest (crisp-edged) filter
+	FilterNearest Filter = iota
+
+	// FilterLinear represents linear filter
+	FilterLinear
 )
 
 func glFilter(filter Filter) opengl.Filter {
diff --git a/input.go b/input.go
index 3321efaab..2e64e23a8 100644
--- a/input.go
+++ b/input.go
@@ -82,11 +82,13 @@ func IsGamepadButtonPressed(id int, button GamepadButton) bool {
 	return ui.CurrentInput().IsGamepadButtonPressed(id, ui.GamepadButton(button))
 }
 
+// Touch represents a pointer state.
 type Touch interface {
 	ID() int
 	Position() (x, y int)
 }
 
+// Touches returns the current touch states.
 func Touches() []Touch {
 	t := ui.CurrentInput().Touches()
 	tt := make([]Touch, len(t))