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, 9 insertions, 1 deletions

diff --git a/source/blender/editors/space_outliner/outliner_intern.h b/source/blender/editors/space_outliner/outliner_intern.h
index cad34c96db4..2256e55a315 100644
--- a/source/blender/editors/space_outliner/outliner_intern.h
+++ b/source/blender/editors/space_outliner/outliner_intern.h
@@ -70,6 +70,13 @@ typedef enum TreeTraversalAction {
  */
 typedef void (*TreeElementReinsertFunc)(const struct Scene *scene, struct TreeElement *insert_element,
                                         struct TreeElement *insert_handle, TreeElementInsertType action);
+/**
+ * Executed on (almost) each mouse move while dragging. It's supposed to give info
+ * if reinserting insert_element before/after/into insert_handle would be allowed.
+ * It's allowed to change the reinsert info here for non const pointers.
+ */
+typedef bool (*TreeElementReinsertPollFunc)(const struct Scene *scene, const struct TreeElement *insert_element,
+                                            struct TreeElement **io_insert_handle, TreeElementInsertType *io_action);
 typedef TreeTraversalAction (*TreeTraversalFunc)(struct TreeElement *te, void *customdata);
 
 
@@ -86,8 +93,9 @@ typedef struct TreeElement {
 	void *directdata;          // Armature Bones, Base, Sequence, Strip...
 	PointerRNA rnaptr;         // RNA Pointer
 
-	/* callbacks */
+	/* callbacks - TODO should be moved into a type (like TreeElementType) */
 	TreeElementReinsertFunc reinsert;
+	TreeElementReinsertPollFunc reinsert_poll;
 
 	struct {
 		TreeElementInsertType insert_type;