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, 31 insertions, 6 deletions

diff --git a/source/blender/editors/interface/interface.c b/source/blender/editors/interface/interface.c
index 254d0909367..c5c2f0e55c4 100644
--- a/source/blender/editors/interface/interface.c
+++ b/source/blender/editors/interface/interface.c
@@ -3352,7 +3352,7 @@ static void ui_but_free(const bContext *C, uiBut *but)
   }
 
   if (but->dragpoin && (but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
-    MEM_freeN(but->dragpoin);
+    WM_drag_data_free(but->dragtype, but->dragpoin);
   }
   ui_but_extra_operator_icons_free(but);
 
@@ -6098,17 +6098,42 @@ void UI_but_drag_set_id(uiBut *but, ID *id)
 {
   but->dragtype = WM_DRAG_ID;
   if ((but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
-    MEM_SAFE_FREE(but->dragpoin);
+    WM_drag_data_free(but->dragtype, but->dragpoin);
     but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
   }
   but->dragpoin = (void *)id;
 }
 
+void UI_but_drag_set_asset(uiBut *but,
+                           const char *name,
+                           const char *path,
+                           int id_type,
+                           int icon,
+                           struct ImBuf *imb,
+                           float scale)
+{
+  wmDragAsset *asset_drag = MEM_mallocN(sizeof(*asset_drag), "wmDragAsset");
+
+  BLI_strncpy(asset_drag->name, name, sizeof(asset_drag->name));
+  asset_drag->path = path;
+  asset_drag->id_type = id_type;
+
+  but->dragtype = WM_DRAG_ASSET;
+  ui_def_but_icon(but, icon, 0); /* no flag UI_HAS_ICON, so icon doesn't draw in button */
+  if ((but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+  }
+  but->dragpoin = asset_drag;
+  but->dragflag |= UI_BUT_DRAGPOIN_FREE;
+  but->imb = imb;
+  but->imb_scale = scale;
+}
+
 void UI_but_drag_set_rna(uiBut *but, PointerRNA *ptr)
 {
   but->dragtype = WM_DRAG_RNA;
   if ((but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
-    MEM_SAFE_FREE(but->dragpoin);
+    WM_drag_data_free(but->dragtype, but->dragpoin);
     but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
   }
   but->dragpoin = (void *)ptr;
@@ -6118,7 +6143,7 @@ void UI_but_drag_set_path(uiBut *but, const char *path, const bool use_free)
 {
   but->dragtype = WM_DRAG_PATH;
   if ((but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
-    MEM_SAFE_FREE(but->dragpoin);
+    WM_drag_data_free(but->dragtype, but->dragpoin);
     but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
   }
   but->dragpoin = (void *)path;
@@ -6131,7 +6156,7 @@ void UI_but_drag_set_name(uiBut *but, const char *name)
 {
   but->dragtype = WM_DRAG_NAME;
   if ((but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
-    MEM_SAFE_FREE(but->dragpoin);
+    WM_drag_data_free(but->dragtype, but->dragpoin);
     but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
   }
   but->dragpoin = (void *)name;
@@ -6149,7 +6174,7 @@ void UI_but_drag_set_image(
   but->dragtype = WM_DRAG_PATH;
   ui_def_but_icon(but, icon, 0); /* no flag UI_HAS_ICON, so icon doesn't draw in button */
   if ((but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
-    MEM_SAFE_FREE(but->dragpoin);
+    WM_drag_data_free(but->dragtype, but->dragpoin);
     but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
   }
   but->dragpoin = (void *)path;