examples: add playing-audio-wav examples

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

examples/playing-audio-wav/playing-audio-wav.go

@@ -0,0 +1,77 @@
+package main
+
+// typedef unsigned char Uint8;
+// void OnAudioPlayback(void *userdata, Uint8 *stream, int len);
+import "C"
+import (
+	"log"
+	"os"
+	"os/signal"
+	"reflect"
+	"syscall"
+	"unsafe"
+
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+var (
+	audio  []byte
+	offset int // We use this to keep track of which part of audio to play
+)
+
+//export OnAudioPlayback
+func OnAudioPlayback(userdata unsafe.Pointer, stream *C.Uint8, length C.int) {
+	n := int(length)
+	hdr := reflect.SliceHeader{Data: uintptr(unsafe.Pointer(stream)), Len: n, Cap: n}
+	buf := *(*[]byte)(unsafe.Pointer(&hdr))
+	for i := 0; i < n; i++ {
+		buf[i] = audio[offset]
+		offset = (offset + 1) % len(audio) // Increase audio offset and loop when it reaches the end
+	}
+}
+
+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()
+
+	// Load WAV audio file
+	tmpaudio, spec := sdl.LoadWAV("../../assets/test.wav")
+	if spec == nil {
+		log.Println(sdl.GetError())
+		return
+	}
+	audio = tmpaudio
+
+	spec.Callback = sdl.AudioCallback(C.OnAudioPlayback)
+
+	// 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
+		}
+	}
+}