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< h2 > Ebiten example - sinewave< / h2 >
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< div class = "card" > < pre class = "card-body" > < code class = "language-go" > // + build example jsgo
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package main
import (
" errors"
" fmt"
" io"
" log"
" math"
" github.com/hajimehoshi/ebiten"
" github.com/hajimehoshi/ebiten/audio"
" github.com/hajimehoshi/ebiten/ebitenutil"
)
const (
screenWidth = 320
screenHeight = 240
sampleRate = 44100
frequency = 440
)
var audioContext *audio.Context
func init() {
var err error
audioContext, err = audio.NewContext(sampleRate)
if err != nil {
log.Fatal(err)
}
}
// stream is an infinite stream of 440 Hz sine wave.
type stream struct {
position int64
}
// Read is io.Reader' s Read.
//
// Read fills the data with sine wave samples.
func (s *stream) Read(data []byte) (int, error) {
if len(data)%4 != 0 {
return 0, errors.New(" len(data) % 4 must be 0" )
}
const length = sampleRate / frequency // TODO: This should be integer?
p := s.position / 4
for i := 0; i < len(data)/4; i+ + {
const max = (1< < 15 - 1) / 2
b := int16(math.Sin(2*math.Pi*float64(p)/length) * max)
data[4*i] = byte(b)
data[4*i+ 1] = byte(b > > 8)
data[4*i+ 2] = byte(b)
data[4*i+ 3] = byte(b > > 8)
p+ +
}
s.position + = int64(len(data))
s.position %= length * 4
return len(data), nil
}
// Seek is io.Seeker' s Seek.
//
// whence must be io.SeekStart or io.SeekCurrent.
func (s *stream) Seek(offset int64, whence int) (int64, error) {
const length = sampleRate / frequency
switch whence {
case io.SeekStart:
s.position = offset
case io.SeekCurrent:
s.position + = offset
default:
return 0, errors.New(" whence must be io.SeekStart or io.SeekCurrent" )
}
s.position %= length * 4
return s.position, nil
}
// Close is io.Closer' s Close.
func (s *stream) Close() error {
return nil
}
var player *audio.Player
func update(screen *ebiten.Image) error {
if player == nil {
// Pass the (infinite) stream to audio.NewPlayer.
// After calling Play, the stream never ends as long as the player object lives.
var err error
player, err = audio.NewPlayer(audioContext, & stream{})
if err != nil {
return err
}
player.Play()
}
if ebiten.IsRunningSlowly() {
return nil
}
msg := fmt.Sprintf(" FPS: %0.2f\nThis is an example using infinite audio stream." , ebiten.CurrentFPS())
ebitenutil.DebugPrint(screen, msg)
return nil
}
func main() {
if err := ebiten.Run(update, screenWidth, screenHeight, 2, " Sine Wave (Ebiten Demo)" ); err != nil {
log.Fatal(err)
}
}
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