[scene] Track hierarchies instead of root transforms

The root transform of each hierarchy can be extracted from the first
transform of the list in the hierarchy, so no information is lost. The
main reason for the change is I discovered (obvious in hindsight) that
deleting root transforms was O(n) due to keeping them in an array, thus
the use of a linked list (I don't expect a hierarchy to be in more than
one such list), and I didn't want the transforms to be in a linked list.

include/QF/scene/hierarchy.h

@@ -45,6 +45,9 @@
 #define null_transform (~0u)
 
 typedef struct hierarchy_s {
+	struct hierarchy_s *next;
+	struct hierarchy_s **prev;
+	struct scene_s *scene;
 	xformset_t  transform;
 	entityset_t entity;
 	uint32set_t childCount;
@@ -61,7 +64,6 @@ typedef struct hierarchy_s {
 	vec4fset_t  localScale;
 	vec4fset_t  worldRotation;
 	vec4fset_t  worldScale;
-	struct scene_s *scene;
 } hierarchy_t;
 
 hierarchy_t *Hierarchy_New (struct scene_s *scene, int createRoot);

include/QF/scene/scene.h

@@ -42,7 +42,7 @@
 
 typedef struct scene_s {
 	struct scene_resources_s *const resources;
-	xformset_t  roots;
+	struct hierarchy_s *hierarchies;
 } scene_t;
 
 scene_t *Scene_NewScene (void);

include/scn_internal.h

@@ -13,7 +13,4 @@ typedef struct scene_resources_s {
 	PR_RESMAP (transform_t) transforms;
 } scene_resources_t;
 
-void scene_add_root (scene_t *scene, transform_t *transform);
-void scene_del_root (scene_t *scene, transform_t *transform);
-
 #endif//__scn_internal_h

libs/scene/hierarchy.c

@@ -403,6 +403,13 @@ Hierarchy_New (scene_t *scene, int createRoot)
 	hierarchy_t *hierarchy = PR_RESNEW_NC (res->hierarchies);
 	hierarchy->scene = scene;
 
+	hierarchy->prev = &scene->hierarchies;
+	hierarchy->next = scene->hierarchies;
+	if (scene->hierarchies) {
+		scene->hierarchies->prev = &hierarchy->next;
+	}
+	scene->hierarchies = hierarchy;
+
 	size_t      grow = 16;
 	DARRAY_INIT (&hierarchy->transform, grow);
 	DARRAY_INIT (&hierarchy->entity, grow);
@@ -432,6 +439,11 @@ Hierarchy_New (scene_t *scene, int createRoot)
 void
 Hierarchy_Delete (hierarchy_t *hierarchy)
 {
+	if (hierarchy->next) {
+		hierarchy->next->prev = hierarchy->prev;
+	}
+	*hierarchy->prev = hierarchy->next;
+
 	scene_resources_t *res = hierarchy->scene->resources;
 	for (size_t i = 0; i < hierarchy->transform.size; i++) {
 		PR_RESFREE (res->transforms, hierarchy->transform.a[i]);

libs/scene/scene.c

@@ -54,8 +54,6 @@ Scene_NewScene (void)
 	res = calloc (1, sizeof (scene_resources_t));
 	*(scene_resources_t **)&scene->resources = res;
 
-	DARRAY_INIT (&scene->roots, 16);
-
 	return scene;
 }
 
@@ -70,8 +68,6 @@ Scene_DeleteScene (scene_t *scene)
 	}
 	free (res->entities._map);
 
-	DARRAY_CLEAR (&scene->roots);
-
 	free (scene->resources);
 	free (scene);
 }
@@ -98,27 +94,6 @@ Scene_GetEntity (scene_t *scene, int id)
 	return PR_RESGET (res->entities, id);
 }
 
-void
-scene_add_root (scene_t *scene, transform_t *transform)
-{
-	if (!Transform_GetParent (transform)) {
-		DARRAY_APPEND (&scene->roots, transform);
-	}
-}
-
-void
-scene_del_root (scene_t *scene, transform_t *transform)
-{
-	if (!Transform_GetParent (transform)) {
-		for (size_t i = 0; i < scene->roots.size; i++) {
-			if (scene->roots.a[i] == transform) {
-				DARRAY_REMOVE_AT (&scene->roots, i);
-				break;
-			}
-		}
-	}
-}
-
 static void
 destroy_entity (scene_t *scene, entity_t *ent)
 {
@@ -154,8 +129,8 @@ Scene_DestroyEntity (scene_t *scene, entity_t *ent)
 void
 Scene_FreeAllEntities (scene_t *scene)
 {
-	for (size_t i = 0; i < scene->roots.size; i++) {
-		hierarchy_t *h = scene->roots.a[i]->hierarchy;
+	while (scene->hierarchies) {
+		hierarchy_t *h = scene->hierarchies;
 		// deleting the root entity deletes all child entities
 		entity_t   *ent = h->entity.a[0];
 		destroy_entity (scene, ent);

libs/scene/transform.c

@@ -58,7 +58,6 @@ Transform_New (scene_t *scene, transform_t *parent)
 	} else {
 		transform->hierarchy = Hierarchy_New (scene, 1);
 		transform->index = 0;
-		scene_add_root (scene, transform);
 	}
 	transform->hierarchy->transform.a[transform->index] = transform;
 	Hierarchy_UpdateMatrices (transform->hierarchy);
@@ -73,7 +72,6 @@ Transform_Delete (transform_t *transform)
 		// hierarchy so deleting it is easier
 		Transform_SetParent (transform, 0);
 	}
-	scene_del_root (transform->scene, transform);
 	// Takes care of freeing the transforms
 	Hierarchy_Delete (transform->hierarchy);
 }
@@ -90,7 +88,6 @@ void
 Transform_SetParent (transform_t *transform, transform_t *parent)
 {
 	if (parent) {
-		scene_del_root (transform->scene, transform);
 		hierarchy_t *hierarchy = transform->hierarchy;
 		uint32_t    index = transform->index;
 		Hierarchy_InsertHierarchy (parent->hierarchy, hierarchy,
@@ -112,7 +109,6 @@ Transform_SetParent (transform_t *transform, transform_t *parent)
 		Hierarchy_InsertHierarchy (new_hierarchy, hierarchy, null_transform,
 								   index);
 		Hierarchy_RemoveHierarchy (hierarchy, index);
-		scene_add_root (transform->scene, transform);
 	}
 }