Merge pull request #1585 from davidgfnet/sdl2audio

Add SDL2 audio backend.

Author: davidgfnet

core/oslib/audiobackend_sdl2.cpp

@@ -0,0 +1,136 @@
+
+#if defined(USE_SDL_AUDIO)
+
+#include <SDL2/SDL.h>
+#include "oslib/audiostream.h"
+#include "stdclass.h"
+
+static SDL_AudioDeviceID audiodev;
+static bool needs_resampling;
+static cResetEvent read_wait;
+static cMutex stream_mutex;
+static struct {
+	uint32_t prevs;
+	uint32_t sample_buffer[2048];
+} audiobuf;
+static unsigned sample_count = 0;
+
+// To easily access samples.
+union Sample { int16_t s[2]; uint32_t l; };
+
+static float InterpolateCatmull4pt3oX(float x0, float x1, float x2, float x3, float t) {
+	return 0.45 * ((2 * x1) + t * ((-x0 + x2) + t * ((2 * x0 - 5 * x1 + 4 * x2 - x3) + t * (-x0 + 3 * x1 - 3 * x2 + x3))));
+}
+
+static void sdl2_audiocb(void* userdata, Uint8* stream, int len) {
+	stream_mutex.Lock();
+	// Wait until there's enough samples to feed the kraken
+	unsigned oslen = len / sizeof(uint32_t);
+	unsigned islen = needs_resampling ? oslen * 16 / 17 : oslen;
+	unsigned minlen = needs_resampling ? islen + 2 : islen;  // Resampler looks ahead by 2 samples.
+
+	if (sample_count < minlen) {
+		// No data, just output a bit of silence for the underrun
+		memset(stream, 0, len);
+        stream_mutex.Unlock();
+		read_wait.Set();
+		return;
+	}
+
+	if (!needs_resampling) {
+		// Just copy bytes for this case.
+		memcpy(stream, &audiobuf.sample_buffer[0], len);
+	}
+	else {
+		// 44.1KHz to 48KHz (actually 46.86KHz) resampling
+		uint32_t *outbuf = (uint32_t*)stream;
+		const float ra = 1.0f / 17;
+		Sample *sbuf = (Sample*)&audiobuf.sample_buffer[0];  // [-1] stores the previous iteration last sample output
+		for (int i = 0; i < islen/16; i++) {
+			*outbuf++ = sbuf[i*16+ 0].l;   // First sample stays at the same location.
+			for (int k = 1; k < 17; k++) {
+				Sample r;
+				// Note we access offset -1 on first iteration, as to access prevs
+				r.s[0] = InterpolateCatmull4pt3oX(sbuf[i*16+k-2].s[0], sbuf[i*16+k-1].s[0], sbuf[i*16+k].s[0], sbuf[i*16+k+1].s[0], 1 - ra*k);
+				r.s[1] = InterpolateCatmull4pt3oX(sbuf[i*16+k-2].s[1], sbuf[i*16+k-1].s[1], sbuf[i*16+k].s[1], sbuf[i*16+k+1].s[1], 1 - ra*k);
+				*outbuf++ = r.l;
+			}
+		}
+		audiobuf.prevs = audiobuf.sample_buffer[islen-1];
+	}
+
+	// Move samples in the buffer and consume them
+	memmove(&audiobuf.sample_buffer[0], &audiobuf.sample_buffer[islen], (sample_count-islen)*sizeof(uint32_t));
+	sample_count -= islen;
+
+	stream_mutex.Unlock();
+	read_wait.Set();
+}
+
+static void sdl2_audio_init() {
+	if (!SDL_WasInit(SDL_INIT_AUDIO))
+		SDL_InitSubSystem(SDL_INIT_AUDIO);
+
+	// Support 44.1KHz (native) but also upsampling to 48KHz
+	SDL_AudioSpec wav_spec, out_spec;
+	memset(&wav_spec, 0, sizeof(wav_spec));
+	wav_spec.freq = 44100;
+	wav_spec.format = AUDIO_S16;
+	wav_spec.channels = 2;
+	wav_spec.samples = 1024;  // Must be power of two
+	wav_spec.callback = sdl2_audiocb;
+	
+	// Try 44.1KHz which should be faster since it's native.
+	audiodev = SDL_OpenAudioDevice(NULL, 0, &wav_spec, &out_spec, 0);
+	if (!audiodev) {
+		needs_resampling = true;
+		wav_spec.freq = 48000;
+		audiodev = SDL_OpenAudioDevice(NULL, 0, &wav_spec, &out_spec, 0);
+		verify(audiodev);
+	}
+}
+
+static u32 sdl2_audio_push(void* frame, u32 samples, bool wait) {
+	// Unpause the device shall it be paused.
+	if (SDL_GetAudioDeviceStatus(audiodev) != SDL_AUDIO_PLAYING)
+		SDL_PauseAudioDevice(audiodev, 0);
+
+	// If wait, then wait for the buffer to be smaller than a certain size.
+	stream_mutex.Lock();
+	if (wait) {
+		while (sample_count + samples > sizeof(audiobuf.sample_buffer)/sizeof(audiobuf.sample_buffer[0])) {
+			stream_mutex.Unlock();
+			read_wait.Wait();
+			read_wait.Reset();
+			stream_mutex.Lock();
+		}
+	}
+
+	// Copy as many samples as possible, drop any remaining (this should not happen usually)
+	unsigned free_samples = sizeof(audiobuf.sample_buffer) / sizeof(audiobuf.sample_buffer[0]) - sample_count;
+	unsigned tocopy = samples < free_samples ? samples : free_samples;
+	memcpy(&audiobuf.sample_buffer[sample_count], frame, tocopy * sizeof(uint32_t));
+	sample_count += tocopy;
+	stream_mutex.Unlock();
+
+	return 1;
+}
+
+static void sdl2_audio_term() {
+    // Stop audio playback.
+	SDL_PauseAudioDevice(audiodev, 1);
+	read_wait.Set();
+}
+
+audiobackend_t audiobackend_sdl2audio = {
+		"sdl2", // Slug
+		"Simple DirectMedia Layer 2 Audio", // Name
+		&sdl2_audio_init,
+		&sdl2_audio_push,
+		&sdl2_audio_term
+};
+
+static bool sdl2audiobe = RegisterAudioBackend(&audiobackend_sdl2audio);
+
+#endif
+

shell/linux/Makefile

@@ -6,6 +6,7 @@ FOR_LINUX :=1
 WEBUI :=1
 USE_OSS := 1
 #USE_PULSEAUDIO := 1
+#USE_SDLAUDIO := 1
 #USE_LIBAO := 1
 USE_EVDEV := 1
 USE_UDEV := 1
@@ -360,6 +361,11 @@ ifdef USE_PULSEAUDIO
     LIBS += `pkg-config --libs libpulse-simple`
 endif
 
+ifdef USE_SDLAUDIO
+    CXXFLAGS += `sdl2-config --cflags` -D USE_SDL_AUDIO
+    LIBS += `sdl2-config --libs`
+endif
+
 ifdef USE_LIBAO
 	CXXFLAGS += `pkg-config --cflags ao` -D USE_LIBAO
 	LIBS += `pkg-config --libs ao`