2022-untitled-game/code/game/engine/audio_mgr.c

void
audio_mgr_startup(void)
{
	g_engine->audio_mgr.sound_count = NULL_HANDLE+1;
}

void
set_listener(vec3 position, vec3 front, vec3 up)
{
	g_engine->audio_mgr.listener.position = position;
	g_engine->audio_mgr.listener.front = front;
	g_engine->audio_mgr.listener.up = up;
}

handle_t
play_sound(audio_source_t sound)
{
	handle_t handle = NULL_HANDLE;

	if (g_engine->audio_mgr.sound_count < MAX_AUDIO_SOURCE_COUNT)
	{
		// Find free handle
		for (int i = NULL_HANDLE+1; i < MAX_AUDIO_SOURCE_COUNT; i++)
		{
			if (g_engine->audio_mgr.handle_to_index_map[i] == NULL_HANDLE)
			{
				handle = i;
				break;
			}
		}

		size_t new_index = g_engine->audio_mgr.sound_count;
		g_engine->audio_mgr.handle_to_index_map[handle] = new_index;
		g_engine->audio_mgr.index_to_handle_map[new_index] = handle;
		g_engine->audio_mgr.sources[new_index] = sound;
		g_engine->audio_mgr.sound_count++;
	}

	return handle;
}

void
stop_sound(int handle)
{
	// Copy element at end into deleted element's place to maintain density
	int stopped_audio_index = g_engine->audio_mgr.handle_to_index_map[handle];
	size_t last_element_index = g_engine->audio_mgr.sound_count - 1;
	g_engine->audio_mgr.sources[stopped_audio_index] = g_engine->audio_mgr.sources[last_element_index];

	// Update maps to point to new locations
	int last_element_handle = g_engine->audio_mgr.index_to_handle_map[last_element_index];
	g_engine->audio_mgr.handle_to_index_map[last_element_handle] = stopped_audio_index;
	g_engine->audio_mgr.index_to_handle_map[stopped_audio_index] = last_element_handle;

	// Mark invalid
	g_engine->audio_mgr.sources[last_element_index].type = AUDIO_TYPE_NULL;
	g_engine->audio_mgr.handle_to_index_map[handle] = NULL_HANDLE;
	g_engine->audio_mgr.index_to_handle_map[last_element_index] = NULL_HANDLE;

	g_engine->audio_mgr.sound_count--;
}

void
update_sound_position(int handle, vec3 position)
{
	(void)handle;(void)position;
	int index = g_engine->audio_mgr.handle_to_index_map[handle];

	transform_t* transform = get_transform(g_engine->audio_mgr.sources[index].transform);
	transform->position = position;
}

void
fill_audio_buffer(uint8_t* buffer, int len)
{
	// Fill with silence ahead of time
	memset(buffer, 0, len);

	int stop_count = 0;
	int stop_handles[MAX_AUDIO_SOURCE_COUNT] = {NULL_HANDLE};

	for (int i = NULL_HANDLE+1; i < g_engine->audio_mgr.sound_count; i++)
	{
		audio_source_t* source = &g_engine->audio_mgr.sources[i];
		sound_t* sound = get_sound(source->sound);

		LOG_ASSERT(sound->byte_count >= source->cursor, "Audio overflow");

		int audio_bytes_remaining = sound->byte_count - source->cursor;
		int bytes_to_fill = (len < audio_bytes_remaining) ? len : audio_bytes_remaining;
		int samples_to_fill = bytes_to_fill / sizeof(*sound->data);

		float* data = (float*)((uint8_t*)sound->data + source->cursor);
		float* buf = (float*)buffer;

		// Calculate angle from listener to source
		float right_gain = 1.0f;
		float left_gain = 1.0f;

		transform_t* transform = get_transform(source->transform);

		switch (source->type)
		{
			case AUDIO_TYPE_MUSIC:
			{
				right_gain = source->volume;
				left_gain = source->volume;
			} break;
			case AUDIO_TYPE_SFX:
			{
				vec3 listener_right = vec3_cross(g_engine->audio_mgr.listener.front, g_engine->audio_mgr.listener.up);
				vec3 listener_left = vec3_negate(listener_right);
				vec3 target = vec3_sub(transform->position, g_engine->audio_mgr.listener.position);
				float distance = vec3_length(target);

				if (distance > 0.0f)
				{
					float attenuation = 1.0f / distance;

					if (attenuation < 0.1f) {
						attenuation = 0.0f;
					} else if (attenuation > 1.0f) {
						attenuation = 1.0f;
					}

					// TODO: Make this better. This is probably very wrong. And I don't fully understand it.
					float angle_left = RAD_TO_DEG(acosf(vec3_dot(listener_left, target)/distance));
					float angle_right = RAD_TO_DEG(acosf(vec3_dot(listener_right, target)/distance));

					left_gain = source->volume * (angle_right/180.0f) * attenuation;
					right_gain = source->volume* (angle_left/180.0f) * attenuation;
				}

			} break;
			default: break;
		}

		for (int j = 0; j < samples_to_fill; j+=2)
		{
			// Left channel
			*buf += *data * left_gain;
			buf++;
			data++;

			// Right channel
			*buf += *data * right_gain;
			buf++;
			data++;
		}

		source->cursor += bytes_to_fill;

		if (source->cursor >= sound->byte_count)
		{
			if (source->type == AUDIO_TYPE_MUSIC) {
				source->cursor = 0;
			} else if (source->type == AUDIO_TYPE_SFX) {
				stop_handles[stop_count++] = g_engine->audio_mgr.index_to_handle_map[i];
			}
		}
	}

	for (int i = 0; i < stop_count; i++) {
		stop_sound(stop_handles[i]);
	}
}