ebiten/examples/audiopanning/main.go

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// Copyright 2020 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
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//go:build example
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// +build example
package main
import (
"bytes"
"fmt"
"image"
_ "image/png"
"io"
"log"
"math"
"time"
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"github.com/hajimehoshi/ebiten/v2"
"github.com/hajimehoshi/ebiten/v2/audio"
"github.com/hajimehoshi/ebiten/v2/audio/vorbis"
"github.com/hajimehoshi/ebiten/v2/ebitenutil"
raudio "github.com/hajimehoshi/ebiten/v2/examples/resources/audio"
"github.com/hajimehoshi/ebiten/v2/examples/resources/images"
)
const (
screenWidth = 640
screenHeight = 480
sampleRate = 32000
)
var ebitenImage *ebiten.Image
type Game struct {
player *audio.Player
panstream *StereoPanStream
// panning goes from -1 to 1
// -1: 100% left channel, 0% right channel
// 0: 100% both channels
// 1: 0% left channel, 100% right channel
panning float64
count int
xpos float64
audioContext *audio.Context
}
func (g *Game) initAudio() {
if g.player != nil {
return
}
if g.audioContext == nil {
g.audioContext = audio.NewContext(sampleRate)
}
// Decode an Ogg file.
// oggS is a decoded io.ReadCloser and io.Seeker.
oggS, err := vorbis.DecodeWithoutResampling(bytes.NewReader(raudio.Ragtime_ogg))
if err != nil {
log.Fatal(err)
}
// Wrap the raw audio with the StereoPanStream
g.panstream = NewStereoPanStreamFromReader(audio.NewInfiniteLoop(oggS, oggS.Length()))
g.player, err = g.audioContext.NewPlayer(g.panstream)
if err != nil {
log.Fatal(err)
}
// Play the infinite-length stream. This never ends.
g.player.Play()
}
// time is whithin the 0 ... 1 range
func lerp(a, b, t float64) float64 {
return a*(1-t) + b*t
}
func (g *Game) Update() error {
g.initAudio()
g.count++
r := float64(g.count) * ((1.0 / 60.0) * 2 * math.Pi) * 0.1 // full cycle every 10 seconds
g.xpos = (float64(screenWidth) / 2) + math.Cos(r)*(float64(screenWidth)/2)
g.panning = lerp(-1, 1, g.xpos/float64(screenWidth))
g.panstream.SetPan(g.panning)
return nil
}
func (g *Game) Draw(screen *ebiten.Image) {
pos := g.player.Current()
msg := fmt.Sprintf(`TPS: %0.2f
This is an example using
stereo audio panning.
Current: %0.2f[s]
Panning: %.2f`, ebiten.ActualTPS(), float64(pos)/float64(time.Second), g.panning)
ebitenutil.DebugPrint(screen, msg)
// draw image to show where the sound is at related to the screen
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(g.xpos-float64(ebitenImage.Bounds().Dx()/2), screenHeight/2)
screen.DrawImage(ebitenImage, op)
}
func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
return screenWidth, screenHeight
}
func main() {
// Decode an image from the image file's byte slice.
// Now the byte slice is generated with //go:generate for Go 1.15 or older.
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// If you use Go 1.16 or newer, it is strongly recommended to use //go:embed to embed the image file.
// See https://pkg.go.dev/embed for more details.
img, _, err := image.Decode(bytes.NewReader(images.Ebiten_png))
if err != nil {
log.Fatal(err)
}
ebitenImage = ebiten.NewImageFromImage(img)
ebiten.SetWindowSize(screenWidth, screenHeight)
ebiten.SetWindowTitle("Audio Panning Loop (Ebitengine Demo)")
g := &Game{}
if err := ebiten.RunGame(g); err != nil {
log.Fatal(err)
}
}
// StereoPanStream is an audio buffer that changes the stereo channel's signal
// based on the Panning.
type StereoPanStream struct {
io.ReadSeeker
pan float64 // -1: left; 0: center; 1: right
buf []byte
}
func (s *StereoPanStream) Read(p []byte) (int, error) {
// If the stream has a buffer that was read in the previous time, use this first.
var bufN int
if len(s.buf) > 0 {
bufN = copy(p, s.buf)
s.buf = s.buf[bufN:]
}
readN, err := s.ReadSeeker.Read(p[bufN:])
if err != nil && err != io.EOF {
return 0, err
}
// Align the buffer size in multiples of 4. The extra part is pushed to the buffer for the
// next time.
totalN := bufN + readN
extra := totalN - totalN/4*4
s.buf = append(s.buf, p[totalN-extra:totalN]...)
alignedN := totalN - extra
// This implementation uses a linear scale, ranging from -1 to 1, for stereo or mono sounds.
// If pan = 0.0, the balance for the sound in each speaker is at 100% left and 100% right.
// When pan is -1.0, only the left channel of the stereo sound is audible, when pan is 1.0,
// only the right channel of the stereo sound is audible.
// https://docs.unity3d.com/ScriptReference/AudioSource-panStereo.html
ls := math.Min(s.pan*-1+1, 1)
rs := math.Min(s.pan+1, 1)
for i := 0; i < alignedN; i += 4 {
lc := int16(float64(int16(p[i])|int16(p[i+1])<<8) * ls)
rc := int16(float64(int16(p[i+2])|int16(p[i+3])<<8) * rs)
p[i] = byte(lc)
p[i+1] = byte(lc >> 8)
p[i+2] = byte(rc)
p[i+3] = byte(rc >> 8)
}
return alignedN, err
}
func (s *StereoPanStream) SetPan(pan float64) {
s.pan = math.Min(math.Max(-1, pan), 1)
}
func (s *StereoPanStream) Pan() float64 {
return s.pan
}
// NewStereoPanStreamFromReader returns a new StereoPanStream with a buffered src.
//
// The src's format must be linear PCM (16bits little endian, 2 channel stereo)
// without a header (e.g. RIFF header). The sample rate must be same as that
// of the audio context.
func NewStereoPanStreamFromReader(src io.ReadSeeker) *StereoPanStream {
return &StereoPanStream{
ReadSeeker: src,
}
}