Function audioCallback

TheForceEngine/TFE_Audio/audioSystem.cpp:458–601

Audio callback

			
	// Audio callback
	static void audioCallback(void* userData, unsigned char* outputBuffer, int bufsize)
	{
		f32* buffer = (f32*)outputBuffer;
		u32 bufferSize = (u32)bufsize;
		u32 frames = bufferSize / (AUDIO_CHANNEL_COUNT * sizeof(f32));

	#if AUDIO_TIMING == 1
		u64 soundIterStart = TFE_System::getCurrentTimeInTicks();
	#endif

		// First clear samples
		memset(buffer, 0, bufferSize);
			   
		SDL_LockMutex(s_mutex);
		// Then call the audio thread callback
		if (s_audioThreadCallback && !s_paused)
		{
			static f32 callbackBuffer[(AUDIO_CALLBACK_BUFFER_SIZE + 2)*AUDIO_CHANNEL_COUNT];	// 256 stereo + oversampling.
			s_audioThreadCallback(callbackBuffer, AUDIO_CALLBACK_BUFFER_SIZE, s_soundFxVolume * c_soundHeadroom);
			// The audio buffer is 1/4 as large as it should be.
			// This means that in-between samples must be interpolated.
			if (!s_silentAudioFrames)
			{
				if (s_upsampleFilter == AUF_NONE)
				{
					upsample4x_point(buffer, callbackBuffer, AUDIO_CALLBACK_BUFFER_SIZE*AUDIO_CHANNEL_COUNT);
				}
				else if (s_upsampleFilter == AUF_LINEAR)
				{
					upsample4x_linear(buffer, callbackBuffer, AUDIO_CALLBACK_BUFFER_SIZE*AUDIO_CHANNEL_COUNT);
				}
			}
		}

		// Then loop through the sources.
		// Note: this is no longer used by Dark Forces. However I decided to keep direct sound support around
		// so it can be used for tools.
		SoundSource* snd = s_sources;
		for (u32 s = 0; s < s_sourceCount && !s_paused; s++, snd++)
		{
			if (!(snd->flags&SND_FLAG_PLAYING)) { continue; }
			assert(snd->buffer->data);

			// Skip sound sample processing the sound is too quiet...
			const u32 sndBufferSize = snd->buffer->size;
			if (snd->volume < SND_CULL_VOLUME)
			{
				// Pretend we played the sound and handle looping.
				snd->sampleIndex += frames;
				if (snd->sampleIndex >= sndBufferSize)
				{
					if (snd->flags&SND_FLAG_LOOPING)
					{
						snd->sampleIndex = (snd->sampleIndex % sndBufferSize) + snd->buffer->loopStart;
					}
					else
					{
						snd->flags &= ~SND_FLAG_PLAYING;