libobs: Add function to allow custom output drawing

Optionally allows drawing directly to the primary output instead of
having to use a source to draw.

libobs/obs.c

@@ -542,6 +542,7 @@ static bool obs_init_data(void)
 	assert(data != NULL);
 
 	pthread_mutex_init_value(&obs->data.displays_mutex);
+	pthread_mutex_init_value(&obs->data.draw_callbacks_mutex);
 
 	if (pthread_mutexattr_init(&attr) != 0)
 		return false;
@@ -559,6 +560,8 @@ static bool obs_init_data(void)
 		goto fail;
 	if (pthread_mutex_init(&data->services_mutex, &attr) != 0)
 		goto fail;
+	if (pthread_mutex_init(&obs->data.draw_callbacks_mutex, NULL) != 0)
+		goto fail;
 	if (!obs_view_init(&data->main_view))
 		goto fail;
 
@@ -614,6 +617,8 @@ static void obs_free_data(void)
 	pthread_mutex_destroy(&data->outputs_mutex);
 	pthread_mutex_destroy(&data->encoders_mutex);
 	pthread_mutex_destroy(&data->services_mutex);
+	pthread_mutex_destroy(&data->draw_callbacks_mutex);
+	da_free(data->draw_callbacks);
 }
 
 static const char *obs_signals[] = {
@@ -1919,3 +1924,31 @@ void obs_get_audio_monitoring_device(const char **name, const char **id)
 	if (id)
 		*id = obs->audio.monitoring_device_id;
 }
+
+void obs_add_main_render_callback(
+		void (*draw)(void *param, uint32_t cx, uint32_t cy),
+		void *param)
+{
+	if (!obs)
+		return;
+
+	struct draw_callback data = {draw, param};
+
+	pthread_mutex_lock(&obs->data.draw_callbacks_mutex);
+	da_push_back(obs->data.draw_callbacks, &data);
+	pthread_mutex_unlock(&obs->data.draw_callbacks_mutex);
+}
+
+void obs_remove_main_render_callback(
+		void (*draw)(void *param, uint32_t cx, uint32_t cy),
+		void *param)
+{
+	if (!obs)
+		return;
+
+	struct draw_callback data = {draw, param};
+
+	pthread_mutex_lock(&obs->data.draw_callbacks_mutex);
+	da_erase_item(obs->data.draw_callbacks, &data);
+	pthread_mutex_unlock(&obs->data.draw_callbacks_mutex);
+}