Implement volume handling

 - Remove obs_source::type because it became redundant now that the
   type is always stored in the obs_source::info variable.

 - Apply presentation volumes of 1.0 and 0.0 to sources when they
   activate/deactivate, respectively.  It also applies that presentation
   volume to all sub-sources, with exception of transition sources.
   Transition sources must apply presentation volume manually to their
   sub-sources with the new transition functions below.

 - Add a "transition_volume" variable to obs_source structure, and add
   three functions for handling volume for transitions:

   * obs_transition_begin_frame
   * obs_source_set_transition_vol
   * obs_transition_end_frame

   Because the to/from targets of a transition source might both contain
   some of the same sources, handling the transitioning of volumes for
   that specific situation becomes an issue.

   So for transitions, instead of modifying the presentation volumes
   directly for both sets of sources, we do this:

   - First, call obs_transition_begin_frame at the beginning of each
     transition frame, which will reset transition volumes for all
     sub-sources to 0.  Presentation volumes remain unchanged.

   - Call obs_source_set_transition_vol on each sub-source, which will
     then add the volume to the transition volume for each source in
     that source's tree.  Presentation volumes still remain unchanged.

   - Then you call obs_trandition_end_frame when complete, which will
     then finally set the presentation volumes to the transition
     volumes.

   For example, let's say that there's one source that's within both the
   "transitioning from" sources and "transition to" sources.  It would
   add both the fade in and fade out volumes to that source, and then
   when the frame is complete, it would set the presentation volume to
   the sum of those two values, rather than set the presentation volume
   for that same source twice which would cause weird volume jittering
   and also set the wrong values.

libobs/obs-internal.h

@@ -179,7 +179,6 @@ struct obs_source {
 
 	/* source-specific data */
 	char                            *name; /* user-defined name */
-	enum obs_source_type            type;
 	obs_data_t                      settings;
 	void                            *data;
 
@@ -217,6 +216,13 @@ struct obs_source {
 	float                           present_volume;
 	int64_t                         sync_offset;
 
+	/* transition volume is meant to store the sum of transitioning volumes
+	 * of a source, i.e. if a source is within both the "to" and "from"
+	 * targets of a transition, it would add both volumes to this variable,
+	 * and then when the transition frame is complete, is applies the value
+	 * to the presentation volume. */
+	float                           transition_volume;
+
 	/* async video data */
 	texture_t                       output_texture;
 	DARRAY(struct source_frame*)    video_frames;

libobs/obs-scene.c

@@ -218,7 +218,6 @@ obs_scene_t obs_scene_create(const char *name)
 	}
 
 	source->name  = bstrdup(name);
-	source->type  = OBS_SOURCE_TYPE_SCENE;
 
 	scene->source = source;
 	obs_source_init(source, &scene_info);
@@ -245,7 +244,7 @@ obs_source_t obs_scene_getsource(obs_scene_t scene)
 
 obs_scene_t obs_scene_fromsource(obs_source_t source)
 {
-	if (source->type != OBS_SOURCE_TYPE_SCENE)
+	if (source->info.type != OBS_SOURCE_TYPE_SCENE)
 		return NULL;
 
 	return source->data;

libobs/obs-source.c

@@ -150,7 +150,6 @@ obs_source_t obs_source_create(enum obs_source_type type, const char *id,
 		goto fail;
 
 	source->name     = bstrdup(name);
-	source->type     = type;
 	source->settings = obs_data_newref(settings);
 	source->data     = info->create(source->settings, source);
 
@@ -329,6 +328,9 @@ static void activate_tree(obs_source_t parent, obs_source_t child, void *param)
 {
 	if (++child->activate_refs == 1)
 		activate_source(child);
+
+	UNUSED_PARAMETER(parent);
+	UNUSED_PARAMETER(param);
 }
 
 static void deactivate_tree(obs_source_t parent, obs_source_t child,
@@ -336,6 +338,9 @@ static void deactivate_tree(obs_source_t parent, obs_source_t child,
 {
 	if (--child->activate_refs == 0)
 		deactivate_source(child);
+
+	UNUSED_PARAMETER(parent);
+	UNUSED_PARAMETER(param);
 }
 
 void obs_source_activate(obs_source_t source)
@@ -345,6 +350,7 @@ void obs_source_activate(obs_source_t source)
 	if (++source->activate_refs == 1) {
 		activate_source(source);
 		obs_source_enum_tree(source, activate_tree, NULL);
+		obs_source_set_present_volume(source, 1.0f);
 	}
 }
 
@@ -355,6 +361,7 @@ void obs_source_deactivate(obs_source_t source)
 	if (--source->activate_refs == 0) {
 		deactivate_source(source);
 		obs_source_enum_tree(source, deactivate_tree, NULL);
+		obs_source_set_present_volume(source, 0.0f);
 	}
 }
 
@@ -1091,7 +1098,7 @@ void obs_source_setname(obs_source_t source, const char *name)
 void obs_source_gettype(obs_source_t source, enum obs_source_type *type,
 		const char **id)
 {
-	if (type) *type = source->type;
+	if (type) *type = source->info.type;
 	if (id)   *id   = source->info.id;
 }
 
@@ -1199,10 +1206,27 @@ void obs_source_setvolume(obs_source_t source, float volume)
 	}
 }
 
+static void set_tree_preset_vol(obs_source_t parent, obs_source_t child,
+		void *param)
+{
+	float *vol = param;
+	child->present_volume = *vol;
+
+	UNUSED_PARAMETER(parent);
+}
+
 void obs_source_set_present_volume(obs_source_t source, float volume)
 {
-	if (source)
+	if (source) {
 		source->present_volume = volume;
+
+		/* don't set the presentation volume of the tree if a
+		 * transition source, let the transition handle presentation
+		 * volume for the child sources itself. */
+		if (source->info.type != OBS_SOURCE_TYPE_TRANSITION)
+			obs_source_enum_tree(source, set_tree_preset_vol,
+					&volume);
+	}
 }
 
 float obs_source_getvolume(obs_source_t source)
@@ -1298,3 +1322,50 @@ void obs_source_remove_child(obs_source_t parent, obs_source_t child)
 	if (parent->activate_refs > 0)
 		obs_source_deactivate(child);
 }
+
+static void reset_transition_vol(obs_source_t parent, obs_source_t child,
+		void *param)
+{
+	child->transition_volume = 0.0f;
+
+	UNUSED_PARAMETER(parent);
+	UNUSED_PARAMETER(param);
+}
+
+static void add_transition_vol(obs_source_t parent, obs_source_t child,
+		void *param)
+{
+	float *vol = param;
+	child->transition_volume += *vol;
+
+	UNUSED_PARAMETER(parent);
+}
+
+static void apply_transition_vol(obs_source_t parent, obs_source_t child,
+		void *param)
+{
+	child->present_volume = child->transition_volume;
+
+	UNUSED_PARAMETER(parent);
+	UNUSED_PARAMETER(param);
+}
+
+void obs_transition_begin_frame(obs_source_t transition)
+{
+	if (!transition) return;
+	obs_source_enum_tree(transition, reset_transition_vol, NULL);
+}
+
+void obs_source_set_transition_vol(obs_source_t source, float vol)
+{
+	if (!source) return;
+
+	add_transition_vol(NULL, source, &vol);
+	obs_source_enum_tree(source, add_transition_vol, &vol);
+}
+
+void obs_transition_end_frame(obs_source_t transition)
+{
+	if (!transition) return;
+	obs_source_enum_tree(transition, apply_transition_vol, NULL);
+}

libobs/obs.h

@@ -560,6 +560,18 @@ EXPORT void obs_source_add_child(obs_source_t parent, obs_source_t child);
  */
 EXPORT void obs_source_remove_child(obs_source_t parent, obs_source_t child);
 
+/** Begins transition frame.  Sets all transitioning volume values to 0.0f. */
+EXPORT void obs_transition_begin_frame(obs_source_t transition);
+
+/**
+ * Adds a transitioning volume value to a source that's being transitioned.
+ * This value is applied to all the sources within the the source.
+ */
+EXPORT void obs_source_set_transition_vol(obs_source_t source, float vol);
+
+/** Ends transition frame and applies new presentation volumes to all sources */
+EXPORT void obs_transition_end_frame(obs_source_t transition);
+
 
 /* ------------------------------------------------------------------------- */
 /* Scenes */