Improve outliner drag&drop feedback by using drop poll callbacks

This way we can ensure the overlay to indicate where the item would be
placed if it was dropped now is always at the correct place and doesn't
mislead the user.

1 files changed, 34 insertions, 10 deletions

diff --git a/source/blender/editors/space_outliner/outliner_tree.c b/source/blender/editors/space_outliner/outliner_tree.c
index 68b533ab31e..1e254b21ff5 100644
--- a/source/blender/editors/space_outliner/outliner_tree.c
+++ b/source/blender/editors/space_outliner/outliner_tree.c
@@ -1306,6 +1306,13 @@ static void outliner_layer_collections_reorder(
 		BLI_assert(0);
 	}
 }
+static bool outliner_layer_collections_reorder_poll(
+        const Scene *UNUSED(scene), const TreeElement *UNUSED(insert_element),
+        TreeElement **io_insert_handle, TreeElementInsertType *UNUSED(io_action))
+{
+	const TreeStoreElem *tselem_handle = TREESTORE(*io_insert_handle);
+	return ELEM(tselem_handle->type, TSE_LAYER_COLLECTION);
+}
 
 static void outliner_scene_collections_reorder(
         const Scene *scene, TreeElement *insert_element, TreeElement *insert_handle, TreeElementInsertType action)
@@ -1314,16 +1321,7 @@ static void outliner_scene_collections_reorder(
 	SceneCollection *sc_insert = insert_element->directdata;
 	SceneCollection *sc_handle = insert_handle->directdata;
 
-	if (sc_handle == sc_master) {
-		/* exception: Can't insert before/after master selection, has to be one of its childs */
-		if (action == TE_INSERT_BEFORE) {
-			sc_handle = sc_master->scene_collections.first;
-		}
-		else if (action == TE_INSERT_AFTER) {
-			sc_handle = sc_master->scene_collections.last;
-		}
-	}
-
+	BLI_assert((action == TE_INSERT_INTO) || (sc_handle != sc_master));
 	if (action == TE_INSERT_BEFORE) {
 		BKE_collection_move_above(scene, sc_handle, sc_insert);
 	}
@@ -1337,6 +1335,30 @@ static void outliner_scene_collections_reorder(
 		BLI_assert(0);
 	}
 }
+static bool outliner_scene_collections_reorder_poll(
+        const Scene *scene, const TreeElement *UNUSED(insert_element),
+        TreeElement **io_insert_handle, TreeElementInsertType *io_action)
+{
+	const TreeStoreElem *tselem_handle = TREESTORE(*io_insert_handle);
+	SceneCollection *sc_master = BKE_collection_master(scene);
+	SceneCollection *sc_handle = (*io_insert_handle)->directdata;
+
+	if (!ELEM(tselem_handle->type, TSE_SCENE_COLLECTION)) {
+		return false;
+	}
+
+	if (sc_handle == sc_master) {
+		/* exception: Can't insert before/after master selection, has to be one of its childs */
+		TreeElement *te_master = *io_insert_handle;
+		if (*io_action == TE_INSERT_BEFORE) {
+			*io_insert_handle = te_master->subtree.first;
+		}
+		else if (*io_action == TE_INSERT_AFTER) {
+			*io_insert_handle = te_master->subtree.last;
+		}
+	}
+	return true;
+}
 
 static void outliner_add_layer_collections_recursive(
         SpaceOops *soops, ListBase *tree, Scene *scene, ListBase *layer_collections, TreeElement *parent_ten,
@@ -1349,6 +1371,7 @@ static void outliner_add_layer_collections_recursive(
 		ten->name = collection->scene_collection->name;
 		ten->directdata = collection;
 		ten->reinsert = outliner_layer_collections_reorder;
+		ten->reinsert_poll = outliner_layer_collections_reorder_poll;
 
 		for (LinkData *link = collection->object_bases.first; link; link = link->next) {
 			outliner_add_element(soops, &ten->subtree, ((Base *)link->data)->object, NULL, 0, 0);
@@ -1370,6 +1393,7 @@ static void outliner_add_scene_collection_init(TreeElement *te, SceneCollection
 	te->name = collection->name;
 	te->directdata = collection;
 	te->reinsert = outliner_scene_collections_reorder;
+	te->reinsert_poll = outliner_scene_collections_reorder_poll;
 }
 
 static void outliner_add_scene_collections_recursive(SpaceOops *soops, ListBase *tree, Scene *scene,