Asset System: Support dragging assets and appending on drop

For the Asset Browser, it needs to be possible to drag assets into various
editors, which may not come from the current .blend file. In other words, the
dragging needs to work with just the asset metadata, without direct access to
the data-block itself.

Idea is simple: When dragging an asset, store the source file-path and
data-block name and when dropping, append the data-block. It uses existing drop
operators, but the function to get the dropped data-block is replaced with one
that returns the local data-block, or, in case of an external asset, appends
the data-block first.

The drop operators need to be adjusted to use this new function that respects
assets. With this patch it only works for dragging assets into the 3D view.

Note that I expect this to be a short-lived change. A refactor like D4071 is
needed to make the drag & drop system more future proof for assets and other
use cases.

Part of the first Asset Browser milestone. Check the #asset_browser_milestone_1
project milestone on developer.blender.org.

Differential Revision: https://developer.blender.org/D9721

Reviewed by: Bastien Montagne, Brecht Van Lommel

1 files changed, 7 insertions, 3 deletions

diff --git a/source/blender/windowmanager/WM_api.h b/source/blender/windowmanager/WM_api.h
index da2115e12fb..1f205a71338 100644
--- a/source/blender/windowmanager/WM_api.h
+++ b/source/blender/windowmanager/WM_api.h
@@ -671,6 +671,7 @@ struct wmDrag *WM_event_start_drag(
     struct bContext *C, int icon, int type, void *poin, double value, unsigned int flags);
 void WM_event_drag_image(struct wmDrag *, struct ImBuf *, float scale, int sx, int sy);
 void WM_drag_free(struct wmDrag *drag);
+void WM_drag_data_free(int dragtype, void *poin);
 void WM_drag_free_list(struct ListBase *lb);
 
 struct wmDropBox *WM_dropbox_add(
@@ -681,9 +682,12 @@ struct wmDropBox *WM_dropbox_add(
 ListBase *WM_dropboxmap_find(const char *idname, int spaceid, int regionid);
 
 /* ID drag and drop */
-void WM_drag_add_ID(struct wmDrag *drag, struct ID *id, struct ID *from_parent);
-struct ID *WM_drag_ID(const struct wmDrag *drag, short idcode);
-struct ID *WM_drag_ID_from_event(const struct wmEvent *event, short idcode);
+void WM_drag_add_local_ID(struct wmDrag *drag, struct ID *id, struct ID *from_parent);
+struct ID *WM_drag_get_local_ID(const struct wmDrag *drag, short idcode);
+struct ID *WM_drag_get_local_ID_from_event(const struct wmEvent *event, short idcode);
+
+struct wmDragAsset *WM_drag_get_asset_data(const struct wmDrag *drag, int idcode);
+struct ID *WM_drag_get_local_ID_or_import_from_asset(const struct wmDrag *drag, int idcode);
 
 /* Set OpenGL viewport and scissor */
 void wmViewport(const struct rcti *winrct);