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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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< 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"
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" io/ioutil"
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" log"
" math"
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" github.com/golang/freetype/truetype"
" golang.org/x/image/font"
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" github.com/hajimehoshi/ebiten"
" github.com/hajimehoshi/ebiten/audio"
" github.com/hajimehoshi/ebiten/ebitenutil"
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" github.com/hajimehoshi/ebiten/inpututil"
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" github.com/hajimehoshi/ebiten/text"
)
var (
arcadeFont font.Face
)
func init() {
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f, err := ebitenutil.OpenFile(" _resources/fonts/arcade_n.ttf" )
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if err != nil {
log.Fatal(err)
}
defer f.Close()
b, err := ioutil.ReadAll(f)
if err != nil {
log.Fatal(err)
}
tt, err := truetype.Parse(b)
if err != nil {
log.Fatal(err)
}
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const (
arcadeFontSize = 8
dpi = 72
)
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arcadeFont = truetype.NewFace(tt, & truetype.Options{
Size: arcadeFontSize,
DPI: dpi,
Hinting: font.HintingFull,
})
}
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const (
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screenWidth = 320
screenHeight = 240
sampleRate = 44100
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baseFreq = 220
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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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}
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// pianoAt returns an i-th sample of piano with the given frequency.
func pianoAt(i int, freq float64) float64 {
// Create piano-like waves with multiple sin waves.
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amp := []float64{1.0, 0.8, 0.6, 0.4, 0.2}
x := []float64{4.0, 2.0, 1.0, 0.5, 0.25}
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v := 0.0
for j := 0; j < len(amp); j+ + {
// Decay
a := amp[j] * math.Exp(-5*float64(i)*freq/baseFreq/(x[j]*sampleRate))
v + = a * math.Sin(2.0*math.Pi*float64(i)*freq*float64(j+ 1)/sampleRate)
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}
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return v / 5.0
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}
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// toBytes returns the 2ch little endian 16bit byte sequence with the given left/right sequence.
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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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var (
pianoNoteSamples = map[int][]byte{}
pianoNoteSamplesInited = false
pianoNoteSamplesInitCh = make(chan struct{})
)
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func init() {
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// Initialize piano data.
// This takes a little long time (especially on browsers),
// so run this asynchronously and notice the progress.
go func() {
// Create a reference data and use this for other frequency.
const refFreq = 110
length := 4 * sampleRate * baseFreq / refFreq
refData := make([]int16, length)
for i := 0; i < length; i+ + {
refData[i] = int16(pianoAt(i, refFreq) * math.MaxInt16)
}
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for i := range keys {
freq := baseFreq * math.Exp2(float64(i-1)/12.0)
// Clculate the wave data for the freq.
length := 4 * sampleRate * baseFreq / int(freq)
l := make([]int16, length)
r := make([]int16, length)
for i := 0; i < length; i+ + {
idx := int(float64(i) * freq / refFreq)
if len(refData) < = idx {
break
}
l[i] = refData[idx]
}
copy(r, l)
n := toBytes(l, r)
pianoNoteSamples[int(freq)] = n
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}
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close(pianoNoteSamplesInitCh)
}()
}
// playNote plays piano sound with the given frequency.
func playNote(freq float64) {
f := int(freq)
p, _ := audio.NewPlayerFromBytes(audioContext, pianoNoteSamples[f])
p.Play()
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}
var (
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pianoImage *ebiten.Image
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)
func init() {
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pianoImage, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
const (
keyWidth = 24
y = 48
)
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whiteKeys := []string{" A" , " S" , " D" , " F" , " G" , " H" , " J" , " K" , " L" }
for i, k := range whiteKeys {
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x := i*keyWidth + 36
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height := 112
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ebitenutil.DrawRect(pianoImage, float64(x), float64(y), float64(keyWidth-1), float64(height), color.White)
text.Draw(pianoImage, k, arcadeFont, x+ 8, y+ height-8, 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
}
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x := i*keyWidth + 24
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height := 64
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ebitenutil.DrawRect(pianoImage, float64(x), float64(y), float64(keyWidth-1), float64(height), color.Black)
text.Draw(pianoImage, k, arcadeFont, x+ 8, y+ height-8, color.White)
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}
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}
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var (
keys = []ebiten.Key{
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,
}
)
func update(screen *ebiten.Image) error {
// The piano data is still being initialized.
// Get the progress if available.
if !pianoNoteSamplesInited {
select {
case < -pianoNoteSamplesInitCh:
pianoNoteSamplesInited = true
default:
}
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}
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if pianoNoteSamplesInited {
for i, key := range keys {
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if !inpututil.IsKeyJustPressed(key) {
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continue
}
playNote(baseFreq * math.Exp2(float64(i-1)/12.0))
}
}
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if ebiten.IsRunningSlowly() {
return nil
}
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screen.Fill(color.RGBA{0x80, 0x80, 0xc0, 0xff})
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screen.DrawImage(pianoImage, 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 >
