Fix T39083: speakers were evaluated multiple times when used in sets

also skip checking all objects for speakers when no speakers are in the
blend file.

source/blender/blenkernel/BKE_sound.h

@@ -134,7 +134,7 @@ void sound_free_waveform(struct bSound *sound);
 
 void sound_read_waveform(struct bSound *sound);
 
-void sound_update_scene(struct Scene *scene);
+void sound_update_scene(struct Main *bmain, struct Scene *scene);
 
 void *sound_get_factory(void *sound);
 

source/blender/blenkernel/intern/scene.c

@@ -1539,9 +1539,6 @@ static void scene_update_tagged_recursive(EvaluationContext *eval_ctx, Main *bma
 	/* scene drivers... */
 	scene_update_drivers(bmain, scene);
 
-	/* update sound system animation */
-	sound_update_scene(scene);
-
 	/* update masking curves */
 	BKE_mask_update_scene(bmain, scene);
 	
@@ -1575,6 +1572,8 @@ void BKE_scene_update_tagged(EvaluationContext *eval_ctx, Main *bmain, Scene *sc
 	 * in the future this should handle updates for all datablocks, not
 	 * only objects and scenes. - brecht */
 	scene_update_tagged_recursive(eval_ctx, bmain, scene, scene);
+	/* update sound system animation (TODO, move to depsgraph) */
+	sound_update_scene(bmain, scene);
 
 	/* extra call here to recalc scene animation (for sequencer) */
 	{
@@ -1680,6 +1679,8 @@ void BKE_scene_update_for_newframe_ex(EvaluationContext *eval_ctx, Main *bmain,
 
 	/* BKE_object_handle_update() on all objects, groups and sets */
 	scene_update_tagged_recursive(eval_ctx, bmain, sce, sce);
+	/* update sound system animation (TODO, move to depsgraph) */
+	sound_update_scene(bmain, sce);
 
 	scene_depsgraph_hack(eval_ctx, sce, sce);
 

source/blender/blenkernel/intern/sound.c

@@ -681,7 +681,7 @@ void sound_read_waveform(bSound *sound)
 	}
 }
 
-void sound_update_scene(struct Scene *scene)
+void sound_update_scene(Main *bmain, struct Scene *scene)
 {
 	Object *ob;
 	Base *base;
@@ -694,6 +694,11 @@ void sound_update_scene(struct Scene *scene)
 	void *handle;
 	float quat[4];
 
+	/* cheap test to skip looping over all objects (no speakers is a common case) */
+	if (BLI_listbase_is_empty(&bmain->speaker)) {
+		goto skip_speakers;
+	}
+
 	for (SETLOOPER(scene, sce_it, base)) {
 		ob = base->object;
 		if (ob->type == OB_SPEAKER) {
@@ -743,6 +748,9 @@ void sound_update_scene(struct Scene *scene)
 		}
 	}
 
+
+skip_speakers:
+
 	while ((handle = AUD_getSet(scene->speaker_handles))) {
 		AUD_removeSequence(scene->sound_scene, handle);
 	}
@@ -808,7 +816,7 @@ void sound_read_waveform(struct bSound *sound) { (void)sound; }
 void sound_init_main(struct Main *bmain) { (void)bmain; }
 void sound_set_cfra(int cfra) { (void)cfra; }
 void sound_update_sequencer(struct Main *main, struct bSound *sound) { (void)main; (void)sound; }
-void sound_update_scene(struct Scene *scene) { (void)scene; }
+void sound_update_scene(struct Main *UNUSED(bmain), struct Scene *UNUSED(scene)) { }
 void sound_update_scene_sound(void *handle, struct bSound *sound) { (void)handle; (void)sound; }
 void sound_update_scene_listener(struct Scene *scene) { (void)scene; }
 void sound_update_fps(struct Scene *scene) { (void)scene; }