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  <h2>Ebiten example - piano</h2>
  <iframe src="piano.content.html" width="640" height="480"></iframe>
  <pre><code>// &#43;build example

package main

import (
    &#34;fmt&#34;
    &#34;image/color&#34;
    &#34;log&#34;
    &#34;math&#34;

    &#34;github.com/hajimehoshi/ebiten&#34;
    &#34;github.com/hajimehoshi/ebiten/audio&#34;
    &#34;github.com/hajimehoshi/ebiten/ebitenutil&#34;
    &#34;github.com/hajimehoshi/ebiten/examples/common&#34;
)

const (
    screenWidth  = 320
    screenHeight = 240
    sampleRate   = 44100
)

var audioContext *audio.Context

func init() {
    var err error
    audioContext, err = audio.NewContext(sampleRate)
    if err != nil {
        log.Fatal(err)
    }
}

var pcm = make([]float64, 4*sampleRate)

const baseFreq = 220

func init() {
    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 &lt; len(pcm); i&#43;&#43; {
        v := 0.0
        twoPiF := 2.0 * math.Pi * baseFreq
        for j := 0; j &lt; len(amp); j&#43;&#43; {
            a := amp[j] * math.Exp(-5*float64(i)/(x[j]*s))
            v &#43;= a * math.Sin(float64(i)*twoPiF*float64(j&#43;1)/s)
        }
        pcm[i] = v / 5.0
    }
}

var (
    noteCache = map[int][]byte{}
)

func toBytes(l, r []int16) []byte {
    if len(l) != len(r) {
        panic(&#34;len(l) must equal to len(r)&#34;)
    }
    b := make([]byte, len(l)*4)
    for i := range l {
        b[4*i] = byte(l[i])
        b[4*i&#43;1] = byte(l[i] &gt;&gt; 8)
        b[4*i&#43;2] = byte(r[i])
        b[4*i&#43;3] = byte(r[i] &gt;&gt; 8)
    }
    return b
}

func addNote(freq float64, vol float64) error {
    // 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 {
        p, err := audio.NewPlayerFromBytes(audioContext, n)
        if err != nil {
            return err
        }
        if err := p.Play(); err != nil {
            return err
        }
        return nil
    }
    length := len(pcm) * baseFreq / f
    l := make([]int16, length)
    r := make([]int16, length)
    j := 0
    jj := 0
    for i := 0; i &lt; len(l); i&#43;&#43; {
        p := pcm[j]
        l[i] = int16(p * vol * math.MaxInt16)
        r[i] = l[i]
        jj &#43;= f
        j = jj / baseFreq
    }
    n := toBytes(l, r)
    noteCache[f] = n
    p, err := audio.NewPlayerFromBytes(audioContext, n)
    if err != nil {
        return err
    }
    if err := p.Play(); err != nil {
        return err
    }
    return nil
}

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,
}

var keyStates = map[ebiten.Key]int{}

func init() {
    for _, key := range keys {
        keyStates[key] = 0
    }
}

func updateInput() {
    for _, key := range keys {
        if !ebiten.IsKeyPressed(key) {
            keyStates[key] = 0
            continue
        }
        keyStates[key]&#43;&#43;
    }
}

var (
    imagePiano *ebiten.Image
)

func init() {
    var err error
    imageEmpty, err := ebiten.NewImage(16, 16, ebiten.FilterNearest)
    if err != nil {
        panic(err)
    }
    if err := imageEmpty.Fill(color.White); err != nil {
        panic(err)
    }
    imagePiano, err = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
    if err != nil {
        panic(err)
    }
    whiteKeys := []string{&#34;A&#34;, &#34;S&#34;, &#34;D&#34;, &#34;F&#34;, &#34;G&#34;, &#34;H&#34;, &#34;J&#34;, &#34;K&#34;, &#34;L&#34;}
    width := 24
    y := 48
    for i, k := range whiteKeys {
        x := i*width &#43; 36
        height := 112
        op := &amp;ebiten.DrawImageOptions{}
        w, h := imageEmpty.Size()
        op.GeoM.Scale(float64(width-1)/float64(w), float64(height)/float64(h))
        op.GeoM.Translate(float64(x), float64(y))
        op.ColorM.Scale(1, 1, 1, 1)
        if err := imagePiano.DrawImage(imageEmpty, op); err != nil {
            panic(err)
        }
        if err := common.ArcadeFont.DrawText(imagePiano, k, x&#43;8, y&#43;height-16, 1, color.Black); err != nil {
            panic(err)
        }
    }

    blackKeys := []string{&#34;Q&#34;, &#34;W&#34;, &#34;&#34;, &#34;R&#34;, &#34;T&#34;, &#34;&#34;, &#34;U&#34;, &#34;I&#34;, &#34;O&#34;}
    for i, k := range blackKeys {
        if k == &#34;&#34; {
            continue
        }
        x := i*width &#43; 24
        height := 64
        op := &amp;ebiten.DrawImageOptions{}
        w, h := imageEmpty.Size()
        op.GeoM.Scale(float64(width-1)/float64(w), float64(height)/float64(h))
        op.GeoM.Translate(float64(x), float64(y))
        op.ColorM.Scale(0, 0, 0, 1)
        if err := imagePiano.DrawImage(imageEmpty, op); err != nil {
            panic(err)
        }
        if err := common.ArcadeFont.DrawText(imagePiano, k, x&#43;8, y&#43;height-16, 1, color.White); err != nil {
            panic(err)
        }
    }
}

func update(screen *ebiten.Image) error {
    updateInput()
    for i, key := range keys {
        if keyStates[key] != 1 {
            continue
        }
        if err := addNote(220*math.Exp2(float64(i-1)/12.0), 1.0); err != nil {
            return err
        }
    }

    if err := screen.Fill(color.RGBA{0x80, 0x80, 0xc0, 0xff}); err != nil {
        return err
    }
    if err := screen.DrawImage(imagePiano, nil); err != nil {
        return err
    }

    if err := ebitenutil.DebugPrint(screen, fmt.Sprintf(&#34;FPS: %0.2f&#34;, ebiten.CurrentFPS())); err != nil {
        return err
    }

    if err := audioContext.Update(); err != nil {
        return err
    }
    return nil
}

func main() {
    if err := ebiten.Run(update, screenWidth, screenHeight, 2, &#34;Piano (Ebiten Demo)&#34;); err != nil {
        log.Fatal(err)
    }
}
</code></pre>

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