UI: Support easy dropping into/onto rows in new tree-view API

Adds an easy way to add drop support for tree-view rows.

Most of the work is handled by the tree-view UI code. The tree items can
simply override a few functions (`can_drop()`, `on_drop()`,
`drop_tooltip()`) to implement their custom drop behavior.

While dragging over a tree-view item that can be dropped into/onto, the
item can show a custom and dynamic tooltip explaining what's gonna
happen on drop.

This isn't used yet, but will soon be for asset catalogs.

See documentation here:
https://wiki.blender.org/wiki/Source/Interface/Views#Further_Customizations

1 files changed, 1 insertions, 0 deletions

diff --git a/source/blender/editors/interface/interface_intern.h b/source/blender/editors/interface/interface_intern.h
index 95e6791b359..8b45d9faae6 100644
--- a/source/blender/editors/interface/interface_intern.h
+++ b/source/blender/editors/interface/interface_intern.h
@@ -1171,6 +1171,7 @@ uiBut *ui_list_row_find_mouse_over(const struct ARegion *region,
 uiBut *ui_list_row_find_from_index(const struct ARegion *region,
                                    const int index,
                                    uiBut *listbox) ATTR_WARN_UNUSED_RESULT;
+uiBut *ui_tree_row_find_mouse_over(const struct ARegion *region, const int x, const int y);
 
 typedef bool (*uiButFindPollFn)(const uiBut *but, const void *customdata);
 uiBut *ui_but_find_mouse_over_ex(const struct ARegion *region,