Asset Browser: Support dragging assets into catalogs

With this it is possible to select any number of assets in the Asset
Browser and drag them into catalogs. The assets will be moved to that
catalog then. However, this will only work in the "Current File" asset
library, since that is the only library that allows changing assets,
which is what's done here.

While dragging assets over the tree row, a tooltip is shown explaining
what's going to happen.

In preparation to this, the new UI tree-view API was already extended
with custom drop support, see 4ee2d9df428d.

----

Changes here to the `wmDrag` code were needed to support dragging multiple
assets. Some of it is considered temporary because a) a proper #AssetHandle
design should replace some ugly parts of this patch and b) the multi-item
support in `wmDrag` isn't that great yet. The entire API will have to be
written anyway (see D4071).

Maniphest Tasks: T91573

Differential Revision: https://developer.blender.org/D12713

Reviewed by: Sybren Stüvel

3 files changed, 133 insertions, 9 deletions

diff --git a/source/blender/windowmanager/WM_api.h b/source/blender/windowmanager/WM_api.h
index 577561017c4..ebb0f803acf 100644
--- a/source/blender/windowmanager/WM_api.h
+++ b/source/blender/windowmanager/WM_api.h
@@ -41,6 +41,8 @@ extern "C" {
 #endif
 
 struct ARegion;
+struct AssetHandle;
+struct AssetLibraryReference;
 struct GHashIterator;
 struct GPUViewport;
 struct ID;
@@ -741,6 +743,9 @@ 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);
 bool WM_drag_is_ID_type(const struct wmDrag *drag, int idcode);
 
+wmDragAsset *WM_drag_create_asset_data(const struct AssetHandle *asset,
+                                       const char *path,
+                                       int import_type);
 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);
 
@@ -748,6 +753,12 @@ void WM_drag_free_imported_drag_ID(struct Main *bmain,
                                    struct wmDrag *drag,
                                    struct wmDropBox *drop);
 
+void WM_drag_add_asset_list_item(wmDrag *drag,
+                                 const struct bContext *C,
+                                 const struct AssetLibraryReference *asset_library_ref,
+                                 const struct AssetHandle *asset);
+const ListBase *WM_drag_asset_list_get(const wmDrag *drag);
+
 const char *WM_drag_get_item_name(struct wmDrag *drag);
 
 /* Set OpenGL viewport and scissor */
diff --git a/source/blender/windowmanager/WM_types.h b/source/blender/windowmanager/WM_types.h
index 588c895c742..7f52bef3203 100644
--- a/source/blender/windowmanager/WM_types.h
+++ b/source/blender/windowmanager/WM_types.h
@@ -915,12 +915,16 @@ typedef void (*wmPaintCursorDraw)(struct bContext *C, int, int, void *customdata
 
 #define WM_DRAG_ID 0
 #define WM_DRAG_ASSET 1
-#define WM_DRAG_RNA 2
-#define WM_DRAG_PATH 3
-#define WM_DRAG_NAME 4
-#define WM_DRAG_VALUE 5
-#define WM_DRAG_COLOR 6
-#define WM_DRAG_DATASTACK 7
+/** The user is dragging multiple assets. This is only supported in few specific cases, proper
+ * multi-item support for dragging isn't supported well yet. Therefore this is kept separate from
+ * #WM_DRAG_ASSET. */
+#define WM_DRAG_ASSET_LIST 2
+#define WM_DRAG_RNA 3
+#define WM_DRAG_PATH 4
+#define WM_DRAG_NAME 5
+#define WM_DRAG_VALUE 6
+#define WM_DRAG_COLOR 7
+#define WM_DRAG_DATASTACK 8
 
 typedef enum wmDragFlags {
   WM_DRAG_NOP = 0,
@@ -953,6 +957,25 @@ typedef struct wmDragAsset {
   struct bContext *evil_C;
 } wmDragAsset;
 
+/**
+ * For some specific cases we support dragging multiple assets (#WM_DRAG_ASSET_LIST). There is no
+ * proper support for dragging multiple items in the `wmDrag`/`wmDrop` API yet, so this is really
+ * just to enable specific features for assets.
+ *
+ * This struct basically contains a tagged union to either store a local ID pointer, or information
+ * about an externally stored asset.
+ */
+typedef struct wmDragAssetListItem {
+  struct wmDragAssetListItem *next, *prev;
+
+  union {
+    struct ID *local_id;
+    wmDragAsset *external_info;
+  } asset_data;
+
+  bool is_external;
+} wmDragAssetListItem;
+
 typedef char *(*WMDropboxTooltipFunc)(struct bContext *,
                                       struct wmDrag *,
                                       const struct wmEvent *event,
@@ -979,6 +1002,8 @@ typedef struct wmDrag {
 
   /** List of wmDragIDs, all are guaranteed to have the same ID type. */
   ListBase ids;
+  /** List of `wmDragAssetListItem`s. */
+  ListBase asset_items;
 } wmDrag;
 
 /**
diff --git a/source/blender/windowmanager/intern/wm_dragdrop.c b/source/blender/windowmanager/intern/wm_dragdrop.c
index c5a89e3ad9f..b76b1672543 100644
--- a/source/blender/windowmanager/intern/wm_dragdrop.c
+++ b/source/blender/windowmanager/intern/wm_dragdrop.c
@@ -46,6 +46,8 @@
 
 #include "BLO_readfile.h"
 
+#include "ED_asset.h"
+
 #include "GPU_shader.h"
 #include "GPU_state.h"
 #include "GPU_viewport.h"
@@ -66,6 +68,8 @@
 
 static ListBase dropboxes = {NULL, NULL};
 
+static void wm_drag_free_asset_data(wmDragAsset **asset_data);
+
 /* drop box maps are stored global for now */
 /* these are part of blender's UI/space specs, and not like keymaps */
 /* when editors become configurable, they can add own dropbox definitions */
@@ -176,6 +180,19 @@ wmDrag *WM_event_start_drag(
       drag->poin = poin;
       drag->flags |= WM_DRAG_FREE_DATA;
       break;
+      /* The asset-list case is special: We get multiple assets from context and attach them to the
+       * drag item. */
+    case WM_DRAG_ASSET_LIST: {
+      const AssetLibraryReference *asset_library = CTX_wm_asset_library_ref(C);
+      ListBase asset_file_links = CTX_data_collection_get(C, "selected_asset_files");
+      LISTBASE_FOREACH (const CollectionPointerLink *, link, &asset_file_links) {
+        const FileDirEntry *asset_file = link->ptr.data;
+        const AssetHandle asset_handle = {asset_file};
+        WM_drag_add_asset_list_item(drag, C, asset_library, &asset_handle);
+      }
+      BLI_freelistN(&asset_file_links);
+      break;
+    }
     default:
       drag->poin = poin;
       break;
@@ -202,10 +219,12 @@ void WM_drag_data_free(int dragtype, void *poin)
 
   /* Not too nice, could become a callback. */
   if (dragtype == WM_DRAG_ASSET) {
-    wmDragAsset *asset_drag = poin;
-    MEM_freeN((void *)asset_drag->path);
+    wmDragAsset *asset_data = poin;
+    wm_drag_free_asset_data(&asset_data);
+  }
+  else {
+    MEM_freeN(poin);
   }
-  MEM_freeN(poin);
 }
 
 void WM_drag_free(wmDrag *drag)
@@ -214,6 +233,12 @@ void WM_drag_free(wmDrag *drag)
     WM_drag_data_free(drag->type, drag->poin);
   }
   BLI_freelistN(&drag->ids);
+  LISTBASE_FOREACH_MUTABLE (wmDragAssetListItem *, asset_item, &drag->asset_items) {
+    if (asset_item->is_external) {
+      wm_drag_free_asset_data(&asset_item->asset_data.external_info);
+    }
+    BLI_freelinkN(&drag->asset_items, asset_item);
+  }
   MEM_freeN(drag);
 }
 
@@ -378,6 +403,27 @@ bool WM_drag_is_ID_type(const wmDrag *drag, int idcode)
   return WM_drag_get_local_ID(drag, idcode) || WM_drag_get_asset_data(drag, idcode);
 }
 
+/**
+ * \note: Does not store \a asset in any way, so it's fine to pass a temporary.
+ */
+wmDragAsset *WM_drag_create_asset_data(const AssetHandle *asset, const char *path, int import_type)
+{
+  wmDragAsset *asset_drag = MEM_mallocN(sizeof(*asset_drag), "wmDragAsset");
+
+  BLI_strncpy(asset_drag->name, ED_asset_handle_get_name(asset), sizeof(asset_drag->name));
+  asset_drag->path = path;
+  asset_drag->id_type = ED_asset_handle_get_id_type(asset);
+  asset_drag->import_type = import_type;
+
+  return asset_drag;
+}
+
+static void wm_drag_free_asset_data(wmDragAsset **asset_data)
+{
+  MEM_freeN((char *)(*asset_data)->path);
+  MEM_SAFE_FREE(*asset_data);
+}
+
 wmDragAsset *WM_drag_get_asset_data(const wmDrag *drag, int idcode)
 {
   if (drag->type != WM_DRAG_ASSET) {
@@ -495,6 +541,48 @@ void WM_drag_free_imported_drag_ID(struct Main *bmain, wmDrag *drag, wmDropBox *
   }
 }
 
+/**
+ * \note: Does not store \a asset in any way, so it's fine to pass a temporary.
+ */
+void WM_drag_add_asset_list_item(
+    wmDrag *drag,
+    /* Context only needed for the hack in #ED_asset_handle_get_full_library_path(). */
+    const bContext *C,
+    const AssetLibraryReference *asset_library_ref,
+    const AssetHandle *asset)
+{
+  if (drag->type != WM_DRAG_ASSET_LIST) {
+    return;
+  }
+
+  /* No guarantee that the same asset isn't added twice. */
+
+  /* Add to list. */
+  wmDragAssetListItem *drag_asset = MEM_callocN(sizeof(*drag_asset), __func__);
+  ID *local_id = ED_asset_handle_get_local_id(asset);
+  if (local_id) {
+    drag_asset->is_external = false;
+    drag_asset->asset_data.local_id = local_id;
+  }
+  else {
+    char asset_blend_path[FILE_MAX_LIBEXTRA];
+    ED_asset_handle_get_full_library_path(C, asset_library_ref, asset, asset_blend_path);
+    drag_asset->is_external = true;
+    drag_asset->asset_data.external_info = WM_drag_create_asset_data(
+        asset, BLI_strdup(asset_blend_path), FILE_ASSET_IMPORT_APPEND);
+  }
+  BLI_addtail(&drag->asset_items, drag_asset);
+}
+
+const ListBase *WM_drag_asset_list_get(const wmDrag *drag)
+{
+  if (drag->type != WM_DRAG_ASSET_LIST) {
+    return NULL;
+  }
+
+  return &drag->asset_items;
+}
+
 /* ************** draw ***************** */
 
 static void wm_drop_operator_draw(const char *name, int x, int y)