SDL2 backend: Use callback instead of a timing loop

The system clock and audio clock aren't necessarily synchronized.

1 files changed, 11 insertions, 83 deletions

diff --git a/Alc/backends/sdl2.c b/Alc/backends/sdl2.c
index 4b2d3acd..c191a528 100644
--- a/Alc/backends/sdl2.c
+++ b/Alc/backends/sdl2.c
@@ -35,15 +35,10 @@ typedef struct ALCsdl2Backend {
     DERIVE_FROM_TYPE(ALCbackend);
 
     SDL_AudioDeviceID deviceID;
-    ALvoid *mBuffer;
-    ALuint mSize;
     ALCboolean quit;
-    ATOMIC(int) killNow;
     althrd_t thread;
 } ALCsdl2Backend;
 
-static int ALCsdl2Backend_mixerProc(void *ptr);
-
 static void ALCsdl2Backend_Construct(ALCsdl2Backend *self, ALCdevice *device);
 static DECLARE_FORWARD(ALCsdl2Backend, ALCbackend, void, Destruct)
 static ALCenum ALCsdl2Backend_open(ALCsdl2Backend *self, const ALCchar *name);
@@ -64,8 +59,6 @@ static void ALCsdl2Backend_Construct(ALCsdl2Backend *self, ALCdevice *device)
     ALCbackend_Construct(STATIC_CAST(ALCbackend, self), device);
     SET_VTABLE2(ALCsdl2Backend, ALCbackend, self);
 
-    self->mBuffer = NULL;
-    self->mSize = 0;
     self->quit = ALC_FALSE;
     if(SDL_WasInit(0) == 0) // Is SDL2 initialized at all?
     {
@@ -74,61 +67,20 @@ static void ALCsdl2Backend_Construct(ALCsdl2Backend *self, ALCdevice *device)
     }
     else if(!SDL_WasInit(SDL_INIT_AUDIO))
         SDL_InitSubSystem(SDL_INIT_AUDIO);
-
-    ATOMIC_INIT(&self->killNow, AL_TRUE);
 }
 
 
-static int ALCsdl2Backend_mixerProc(void *ptr)
+static void ALCsdl2Backend_audioCallback(void *ptr, Uint8* stream, int len)
 {
     ALCsdl2Backend *self = (ALCsdl2Backend*)ptr;
     ALCdevice *device = STATIC_CAST(ALCbackend, self)->mDevice;
-    struct timespec now, start;
-    ALuint64 avail, done;
-    const long restTime = (long)((ALuint64)device->UpdateSize * 1000000000 /
-                                 device->Frequency / 2);
-
-    SetRTPriority();
-    althrd_setname(althrd_current(), MIXER_THREAD_NAME);
-
-    done = 0;
-    if(altimespec_get(&start, AL_TIME_UTC) != AL_TIME_UTC)
-    {
-        ERR("Failed to get starting time\n");
-        return 1;
-    }
-    while(!ATOMIC_LOAD(&self->killNow, almemory_order_acquire) &&
-          ATOMIC_LOAD(&device->Connected, almemory_order_acquire))
-    {
-        if(altimespec_get(&now, AL_TIME_UTC) != AL_TIME_UTC)
-        {
-            ERR("Failed to get current time\n");
-            return 1;
-        }
-
-        avail  = (now.tv_sec - start.tv_sec) * device->Frequency;
-        avail += (ALint64)(now.tv_nsec - start.tv_nsec) * device->Frequency / 1000000000;
-        if(avail < done)
-        {
-            /* Oops, time skipped backwards. Reset the number of samples done
-             * with one update available since we (likely) just came back from
-             * sleeping. */
-            done = avail - device->UpdateSize;
-        }
-
-        if(avail-done < device->UpdateSize)
-            al_nssleep(restTime);
-        else while(avail-done >= device->UpdateSize)
-        {
-            ALCsdl2Backend_lock(self);
-            aluMixData(device, self->mBuffer, device->UpdateSize);
-            SDL_QueueAudio(self->deviceID, self->mBuffer, self->mSize);
-            ALCsdl2Backend_unlock(self);
-            done += device->UpdateSize;
-        }
-    }
-
-    return 0;
+    ALsizei frameSize = FrameSizeFromDevFmt(
+        device->FmtChans, device->FmtType, device->AmbiOrder
+    );
+    assert(len % frameSize == 0);
+    ALCsdl2Backend_lock(self);
+    aluMixData(device, stream, len / frameSize);
+    ALCsdl2Backend_unlock(self);
 }
 
 static ALCenum ALCsdl2Backend_open(ALCsdl2Backend *self, const ALCchar *name)
@@ -140,6 +92,8 @@ static ALCenum ALCsdl2Backend_open(ALCsdl2Backend *self, const ALCchar *name)
     want.format = AUDIO_F32;
     want.channels = 2;
     want.samples = device->UpdateSize;
+    want.callback = ALCsdl2Backend_audioCallback;
+    want.userdata = self;
 
     if(!name)
         name = SDL_GetAudioDeviceName(0, 0);
@@ -161,39 +115,13 @@ static ALCboolean ALCsdl2Backend_reset(ALCsdl2Backend *self)
 
 static ALCboolean ALCsdl2Backend_start(ALCsdl2Backend *self)
 {
-    ALCdevice *device = STATIC_CAST(ALCbackend, self)->mDevice;
-    self->mSize = device->UpdateSize * FrameSizeFromDevFmt(
-        device->FmtChans, device->FmtType, device->AmbiOrder
-    );
-    self->mBuffer = malloc(self->mSize);
-    if(!self->mBuffer)
-    {
-        ERR("Buffer malloc failed\n");
-        return ALC_FALSE;
-    }
-
-    ATOMIC_STORE(&self->killNow, AL_FALSE, almemory_order_release);
-    if(althrd_create(&self->thread, ALCsdl2Backend_mixerProc, self) != althrd_success)
-    {
-        free(self->mBuffer);
-        self->mBuffer = NULL;
-        self->mSize = 0;
-        return ALC_FALSE;
-    }
     SDL_PauseAudioDevice(self->deviceID, 0);
     return ALC_TRUE;
 }
 
 static void ALCsdl2Backend_stop(ALCsdl2Backend *self)
 {
-    int res;
-
-    if(ATOMIC_EXCHANGE(&self->killNow, AL_TRUE, almemory_order_acq_rel))
-        return;
-    althrd_join(self->thread, &res);
-
-    free(self->mBuffer);
-    self->mBuffer = NULL;
+    SDL_PauseAudioDevice(self->deviceID, 1);
     if(self->quit)
         SDL_Quit();
 }