example/audio: add sample audio app

This app makes a sound as the gopher hits the edges of the screen.

Change-Id: I85c7d55ec88b1a9faec5dfb7b29e03d1149f5d65
Reviewed-on: https://go-review.googlesource.com/9698
Reviewed-by: Nigel Tao <nigeltao@golang.org>

example/audio/main.go

@@ -0,0 +1,185 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// An app that makes a sound as the gopher hits the walls of the screen.
+//
+// Note: This demo is an early preview of Go 1.5. In order to build this
+// program as an Android APK using the gomobile tool.
+//
+// See http://godoc.org/golang.org/x/mobile/cmd/gomobile to install gomobile.
+//
+// Get the audio example and use gomobile to build or install it on your device.
+//
+//   $ go get -d golang.org/x/mobile/example/audio
+//   $ gomobile build golang.org/x/mobile/example/audio # will build an APK
+//
+//   # plug your Android device to your computer or start an Android emulator.
+//   # if you have adb installed on your machine, use gomobile install to
+//   # build and deploy the APK to an Android target.
+//   $ gomobile install golang.org/x/mobile/example/audio
+//
+// Additionally, you can run the sample on your desktop environment
+// by using the go tool.
+//
+//   $ go install golang.org/x/mobile/example/audio && audio
+//
+// On Linux, you need to install OpenAL developer library by
+// running the command below.
+//
+//   $ apt-get install libopenal-dev
+package main
+
+import (
+	"image"
+	"log"
+	"time"
+
+	_ "image/jpeg"
+
+	"golang.org/x/mobile/app"
+	"golang.org/x/mobile/app/debug"
+	"golang.org/x/mobile/audio"
+	"golang.org/x/mobile/f32"
+	"golang.org/x/mobile/geom"
+	"golang.org/x/mobile/gl"
+	"golang.org/x/mobile/sprite"
+	"golang.org/x/mobile/sprite/clock"
+	"golang.org/x/mobile/sprite/glsprite"
+)
+
+const (
+	width  = 72
+	height = 60
+)
+
+var (
+	startClock = time.Now()
+	lastClock  = clock.Time(-1)
+
+	eng   = glsprite.Engine()
+	scene *sprite.Node
+
+	player *audio.Player
+)
+
+func main() {
+	app.Run(app.Callbacks{
+		Start: start,
+		Stop:  stop,
+		Draw:  draw,
+	})
+}
+
+func start() {
+	rc, err := app.Open("boing.wav")
+	if err != nil {
+		log.Fatal(err)
+	}
+	player, err = audio.NewPlayer(rc, audio.Mono16, 44100)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func stop() {
+	player.Destroy()
+}
+
+func draw() {
+	if scene == nil {
+		loadScene()
+	}
+
+	now := clock.Time(time.Since(startClock) * 60 / time.Second)
+	if now == lastClock {
+		// TODO: figure out how to limit draw callbacks to 60Hz instead of
+		// burning the CPU as fast as possible.
+		// TODO: (relatedly??) sync to vblank?
+		return
+	}
+	lastClock = now
+
+	gl.ClearColor(1, 1, 1, 1)
+	gl.Clear(gl.COLOR_BUFFER_BIT)
+	eng.Render(scene, now)
+	debug.DrawFPS()
+}
+
+func newNode() *sprite.Node {
+	n := &sprite.Node{}
+	eng.Register(n)
+	scene.AppendChild(n)
+	return n
+}
+
+func loadScene() {
+	gopher := loadGopher()
+	scene = &sprite.Node{}
+	eng.Register(scene)
+	eng.SetTransform(scene, f32.Affine{
+		{1, 0, 0},
+		{0, 1, 0},
+	})
+
+	var x, y float32
+	dx, dy := float32(1), float32(1)
+
+	n := newNode()
+	n.Arranger = arrangerFunc(func(eng sprite.Engine, n *sprite.Node, t clock.Time) {
+		eng.SetSubTex(n, gopher)
+
+		if x < 0 {
+			dx = 1
+			boing()
+		}
+		if y < 0 {
+			dy = 1
+			boing()
+		}
+		if x+width > float32(geom.Width) {
+			dx = -1
+			boing()
+		}
+		if y+height > float32(geom.Height) {
+			dy = -1
+			boing()
+		}
+
+		x += dx
+		y += dy
+
+		eng.SetTransform(n, f32.Affine{
+			{width, 0, x},
+			{0, height, y},
+		})
+	})
+}
+
+func boing() {
+	// TODO(jbd): the sound explodes at seek, volume down and seek?
+	player.Seek(0)
+	player.Play()
+}
+
+func loadGopher() sprite.SubTex {
+	a, err := app.Open("gopher.jpeg")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer a.Close()
+
+	img, _, err := image.Decode(a)
+	if err != nil {
+		log.Fatal(err)
+	}
+	t, err := eng.LoadTexture(img)
+	if err != nil {
+		log.Fatal(err)
+	}
+	return sprite.SubTex{t, image.Rect(0, 0, 360, 300)}
+}
+
+type arrangerFunc func(e sprite.Engine, n *sprite.Node, t clock.Time)
+
+func (a arrangerFunc) Arrange(e sprite.Engine, n *sprite.Node, t clock.Time) { a(e, n, t) }