.go

package main

import (
	"math"
	"time"

	"github.com/faiface/pixel"
	"github.com/faiface/pixel/audio"
	"github.com/faiface/pixel/audio/speaker"
	"github.com/faiface/pixel/pixelgl"
)

func sin(freq, volume float64) audio.Streamer {
	t := 0.0
	dt := 1.0 / audio.SampleRate
	return audio.StreamerFunc(func(samples [][2]float64) (n int, ok bool) {
		for i := range samples {
			val := math.Sin(math.Pi*freq*t) * volume
			samples[i][0] = val
			samples[i][1] = val
			t += dt
		}
		return len(samples), true
	})
}

func run() {
	speaker.Init(time.Second / 20)
	go func() {
		for {
			speaker.Update()
		}
	}()

	cfg := pixelgl.WindowConfig{
		Title:  "Piano",
		Bounds: pixel.R(0, 0, 800, 600),
		VSync:  true,
	}
	win, err := pixelgl.NewWindow(cfg)
	if err != nil {
		panic(err)
	}

	keysTones := map[pixelgl.Button]float64{
		pixelgl.KeyA: 523.25,
		pixelgl.KeyS: 554.37,
		pixelgl.KeyD: 587.33,
		pixelgl.KeyF: 622.25,
		pixelgl.KeyG: 659.25,
		pixelgl.KeyH: 698.46,
		pixelgl.KeyJ: 739.99,
		pixelgl.KeyK: 783.99,
		pixelgl.KeyL: 830.61,
	}

	prevKey := pixelgl.Button(-1)

	for !win.Closed() {
		newKey := pixelgl.Button(-1)
		for key := range keysTones {
			if win.Pressed(key) {
				newKey = key
			}
		}
		if prevKey != newKey {
			if newKey == -1 {
				speaker.Play(nil)
			} else {
				speaker.Play(sin(keysTones[newKey], 0.3))
			}
			prevKey = newKey
		}

		win.Update()
	}
}

func main() {
	pixelgl.Run(run)
}