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<!DOCTYPE html>
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< meta name = "description" content = "Ebiten example - piano" >
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< title > Ebiten example - piano< / title >
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< li class = "nav-item" > < a class = "nav-link" href = "https://github.com/hajimehoshi/ebiten" > GitHub< / a > < / li >
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< main > < div class = "container" >
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< h2 > Ebiten example - piano< / h2 >
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< iframe src = "piano.content.html" width = "640" height = "480" > < / iframe >
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< div class = "card" > < pre class = "card-body" > < code class = "language-go" > // + build example
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package main
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import (
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" fmt"
" image/color"
" log"
" math"
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" github.com/hajimehoshi/ebiten"
" github.com/hajimehoshi/ebiten/audio"
" github.com/hajimehoshi/ebiten/ebitenutil"
" github.com/hajimehoshi/ebiten/examples/common"
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)
const (
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screenWidth = 320
screenHeight = 240
sampleRate = 44100
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)
var audioContext *audio.Context
func init() {
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var err error
audioContext, err = audio.NewContext(sampleRate)
if err != nil {
log.Fatal(err)
}
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}
var pcm = make([]float64, 4*sampleRate)
const baseFreq = 220
func init() {
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s := float64(sampleRate)
amp := []float64{1.0, 0.8, 0.6, 0.4, 0.2}
x := []float64{4.0, 2.0, 1.0, 0.5, 0.25}
for i := 0; i < len(pcm); i+ + {
v := 0.0
twoPiF := 2.0 * math.Pi * baseFreq
for j := 0; j < len(amp); j+ + {
a := amp[j] * math.Exp(-5*float64(i)/(x[j]*s))
v + = a * math.Sin(float64(i)*twoPiF*float64(j+ 1)/s)
}
pcm[i] = v / 5.0
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}
}
var (
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noteCache = map[int][]byte{}
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)
func toBytes(l, r []int16) []byte {
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if len(l) != len(r) {
panic(" len(l) must equal to len(r)" )
}
b := make([]byte, len(l)*4)
for i := range l {
b[4*i] = byte(l[i])
b[4*i+ 1] = byte(l[i] > > 8)
b[4*i+ 2] = byte(r[i])
b[4*i+ 3] = byte(r[i] > > 8)
}
return b
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}
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func addNote(freq float64, vol float64) {
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// TODO: Call Close method of *audio.Player.
// However, this works without Close because Close is automatically called when GC
// collects a *audio.Player object.
f := int(freq)
if n, ok := noteCache[f]; ok {
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p, _ := audio.NewPlayerFromBytes(audioContext, n)
p.Play()
return
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}
length := len(pcm) * baseFreq / f
l := make([]int16, length)
r := make([]int16, length)
j := 0
jj := 0
for i := 0; i < len(l); i+ + {
p := pcm[j]
l[i] = int16(p * vol * math.MaxInt16)
r[i] = l[i]
jj + = f
j = jj / baseFreq
}
n := toBytes(l, r)
noteCache[f] = n
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p, _ := audio.NewPlayerFromBytes(audioContext, n)
p.Play()
return
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}
var keys = []ebiten.Key{
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ebiten.KeyQ,
ebiten.KeyA,
ebiten.KeyW,
ebiten.KeyS,
ebiten.KeyD,
ebiten.KeyR,
ebiten.KeyF,
ebiten.KeyT,
ebiten.KeyG,
ebiten.KeyH,
ebiten.KeyU,
ebiten.KeyJ,
ebiten.KeyI,
ebiten.KeyK,
ebiten.KeyO,
ebiten.KeyL,
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}
var keyStates = map[ebiten.Key]int{}
func init() {
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for _, key := range keys {
keyStates[key] = 0
}
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}
func updateInput() {
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for _, key := range keys {
if !ebiten.IsKeyPressed(key) {
keyStates[key] = 0
continue
}
keyStates[key]+ +
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}
}
var (
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imagePiano *ebiten.Image
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)
func init() {
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imagePiano, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
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whiteKeys := []string{" A" , " S" , " D" , " F" , " G" , " H" , " J" , " K" , " L" }
width := 24
y := 48
for i, k := range whiteKeys {
x := i*width + 36
height := 112
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ebitenutil.DrawRect(imagePiano, float64(x), float64(y), float64(width-1), float64(height), color.White)
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common.ArcadeFont.DrawText(imagePiano, k, x+ 8, y+ height-16, 1, color.Black)
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}
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blackKeys := []string{" Q" , " W" , " " , " R" , " T" , " " , " U" , " I" , " O" }
for i, k := range blackKeys {
if k == " " {
continue
}
x := i*width + 24
height := 64
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ebitenutil.DrawRect(imagePiano, float64(x), float64(y), float64(width-1), float64(height), color.Black)
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common.ArcadeFont.DrawText(imagePiano, k, x+ 8, y+ height-16, 1, color.White)
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}
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}
func update(screen *ebiten.Image) error {
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updateInput()
for i, key := range keys {
if keyStates[key] != 1 {
continue
}
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addNote(220*math.Exp2(float64(i-1)/12.0), 1.0)
}
if err := audioContext.Update(); err != nil {
return err
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}
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if ebiten.IsRunningSlowly() {
return nil
}
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screen.Fill(color.RGBA{0x80, 0x80, 0xc0, 0xff})
screen.DrawImage(imagePiano, nil)
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ebitenutil.DebugPrint(screen, fmt.Sprintf(" FPS: %0.2f" , ebiten.CurrentFPS()))
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return nil
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}
func main() {
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if err := ebiten.Run(update, screenWidth, screenHeight, 2, " Piano (Ebiten Demo)" ); err != nil {
log.Fatal(err)
}
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}
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< / code > < / pre > < / div >
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< / div > < / main >
< footer > < div class = "container" >
< p > © 2013 Hajime Hoshi< / p >
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< p > Code is licensed under < a href = "https://github.com/hajimehoshi/ebiten/blob/master/LICENSE" > the Apache License 2.0< / a > .< / p >
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< p > The content of this page is licensed under < a href = "https://creativecommons.org/licenses/by/4.0/" > the Creative Commons Attribution 4.0 License< / a > .< / p >
< / div > < / footer >
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< script src = "../scripts/highlight.pack.js" > < / script >
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< script > hljs . initHighlightingOnLoad ( ) ; < / script >
