examples: add playing-audio examples

Signed-off-by: Lilis Iskandar <lilis@veand.co>

examples/playing-audio/playing-audio.go

@@ -0,0 +1,85 @@
+package main
+
+// typedef unsigned char Uint8;
+// void SineWave(void *userdata, Uint8 *stream, int len);
+import "C"
+import (
+	"log"
+	"math"
+	"os"
+	"os/signal"
+	"reflect"
+	"syscall"
+	"unsafe"
+
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+const (
+	DefaultFrequency = 16000
+	DefaultFormat    = sdl.AUDIO_S16
+	DefaultChannels  = 2
+	DefaultSamples   = 512
+
+	toneHz = 440
+	dPhase = 2 * math.Pi * toneHz / DefaultSamples
+)
+
+//export SineWave
+func SineWave(userdata unsafe.Pointer, stream *C.Uint8, length C.int) {
+	n := int(length) / 2
+	hdr := reflect.SliceHeader{Data: uintptr(unsafe.Pointer(stream)), Len: n, Cap: n}
+	buf := *(*[]C.ushort)(unsafe.Pointer(&hdr))
+
+	var phase float64
+	for i := 0; i < n; i++ {
+		phase += dPhase
+		sample := C.ushort((math.Sin(phase) + 0.999999) * 32768)
+		buf[i] = sample
+	}
+}
+
+func main() {
+	var dev sdl.AudioDeviceID
+	var err error
+
+	// Initialize SDL2
+	if err := sdl.Init(sdl.INIT_AUDIO); err != nil {
+		log.Println(err)
+		return
+	}
+	defer sdl.Quit()
+
+	// Specify the configuration for our default playback device
+	spec := sdl.AudioSpec{
+		Freq:     DefaultFrequency,
+		Format:   DefaultFormat,
+		Channels: DefaultChannels,
+		Samples:  DefaultSamples,
+		Callback: sdl.AudioCallback(C.SineWave),
+	}
+
+	// Open default playback device
+	if dev, err = sdl.OpenAudioDevice("", false, &spec, nil, 0); err != nil {
+		log.Println(err)
+		return
+	}
+	defer sdl.CloseAudioDevice(dev)
+
+	// Start playback audio
+	sdl.PauseAudioDevice(dev, false)
+
+	// Listen to OS signals
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
+
+	// Run infinite loop until we receive SIGINT or SIGTERM!
+	running := true
+	for running {
+		select {
+		case sig := <-c:
+			log.Printf("Received signal %v. Exiting.\n", sig)
+			running = false
+		}
+	}
+}