examples: Add audio_microphone example

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

examples/audio_microphone/main.c

@@ -0,0 +1,6 @@
+#include "_cgo_export.h"
+
+void cOnAudio(void *userdata, unsigned char *stream, int len)
+{
+	onAudio(stream, len);
+}

examples/audio_microphone/main.go

@@ -0,0 +1,87 @@
+package main
+
+/*
+// NOTE: Only works on SDL2 2.0.5 and above!
+
+extern void cOnAudio(void *userdata, unsigned char *stream, int len);
+*/
+import "C"
+import (
+	"fmt"
+	"os"
+	"os/signal"
+	"reflect"
+	"syscall"
+	"unsafe"
+
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+var (
+	want, have sdl.AudioSpec
+)
+
+func makeBytes(raw *C.uchar, len int) (out []byte) {
+	in := asBytes(raw, len)
+	out = make([]byte, len)
+
+	for i := 0; i < len; i++ {
+		out[i] = in[i]
+	}
+
+	return
+}
+
+//export onAudio
+func onAudio(raw *C.uchar, sz int) {
+	data := makeBytes(raw, sz)
+	fmt.Println("Received audio:", len(data), "bytes")
+}
+
+func asBytes(in *C.uchar, len int) (p []byte) {
+	sliceHeader := (*reflect.SliceHeader)(unsafe.Pointer(&p))
+	sliceHeader.Cap = len
+	sliceHeader.Len = len
+	sliceHeader.Data = uintptr(unsafe.Pointer(in))
+	return
+}
+
+func open() (dev sdl.AudioDeviceID, err error) {
+	var want, have sdl.AudioSpec
+
+	want.Callback = sdl.AudioCallback(C.cOnAudio)
+	want.Channels = 1
+	want.Format = sdl.AUDIO_S16SYS
+	want.Freq = 16000
+	want.Samples = 512
+
+	dev, err = sdl.OpenAudioDevice("", true, &want, &have, 0)
+	if err != nil {
+		return
+	}
+
+	sdl.PauseAudioDevice(dev, false)
+
+	return
+}
+
+func main() {
+	sdl.Init(sdl.INIT_AUDIO)
+
+	sigchan := make(chan os.Signal, 1)
+	signal.Notify(sigchan, os.Interrupt, syscall.SIGTERM)
+
+	func() {
+		dev, err := open()
+		if err != nil {
+			panic(err)
+		}
+		defer sdl.CloseAudioDevice(dev)
+
+		<-sigchan
+
+		fmt.Println("Exiting..")
+	}()
+
+	sdl.Quit()
+}