source/blender/editors/include/UI_abstract_view.hh

@@ -12,34 +12,44 @@
  * - Custom context menus
  * - Notifier listening
  * - Drag controllers (dragging view items)
- * - Drop controllers (dropping onto/into view items)
+ * - Drop targets (dropping onto/into view items)
  */
 
 #pragma once
 
 #include <array>
 #include <memory>
+#include <optional>
 
 #include "DNA_defs.h"
+#include "DNA_vec_types.h"
 
 #include "BLI_span.hh"
 #include "BLI_string_ref.hh"
 
+#include "UI_interface.hh"
+
 struct bContext;
 struct uiBlock;
 struct uiLayout;
 struct uiViewItemHandle;
+struct ViewLink;
 struct wmDrag;
 struct wmNotifier;
 
 namespace blender::ui {
 
 class AbstractViewItem;
-class AbstractViewItemDropController;
+class AbstractViewItemDropTarget;
 class AbstractViewItemDragController;
 
+/** The view drop target can share logic with the view item drop target for now, so just an alias.
+ */
+using AbstractViewDropTarget = AbstractViewItemDropTarget;
+
 class AbstractView {
   friend class AbstractViewItem;
+  friend struct ::ViewLink;
 
   bool is_reconstructed_ = false;
   /**
@@ -51,9 +61,21 @@ class AbstractView {
    */
   std::unique_ptr<std::array<char, MAX_NAME>> rename_buffer_;
 
+  /* See #get_bounds(). */
+  std::optional<rcti> bounds_;
+
  public:
   virtual ~AbstractView() = default;
 
+  /**
+   * If a view wants to support dropping data into it, it has to return a drop target here.
+   * That is an object implementing #AbstractViewDropTarget.
+   *
+   * \note This drop target may be requested for each event. The view doesn't keep the drop target
+   *       around currently. So it cannot contain persistent state.
+   */
+  virtual std::unique_ptr<AbstractViewDropTarget> create_drop_target() const;
+
   /** Listen to a notifier, returning true if a redraw is needed. */
   virtual bool listen(const wmNotifier &) const;
 
@@ -70,6 +92,11 @@ class AbstractView {
   void end_renaming();
   Span<char> get_rename_buffer() const;
   MutableSpan<char> get_rename_buffer();
+  /**
+   * Get the rectangle containing all the view items that are in the layout, in button space.
+   * Updated as part of #UI_block_end(), before that it's unset.
+   */
+  std::optional<rcti> get_bounds() const;
 
  protected:
   AbstractView() = default;
@@ -133,13 +160,13 @@ class AbstractViewItem {
    */
   virtual std::unique_ptr<AbstractViewItemDragController> create_drag_controller() const;
   /**
-   * If an item wants to support dropping data into it, it has to return a drop controller here.
+   * If an item wants to support dropping data into it, it has to return a drop target here.
-   * That is an object implementing #AbstractViewItemDropController.
+   * That is an object implementing #AbstractViewItemDropTarget.
    *
-   * \note This drop controller may be requested for each event. The view doesn't keep a drop
+   * \note This drop target may be requested for each event. The view doesn't keep a drop target
-   *       controller around currently. So it can not contain persistent state.
+   *       around currently. So it can not contain persistent state.
    */
-  virtual std::unique_ptr<AbstractViewItemDropController> create_drop_controller() const;
+  virtual std::unique_ptr<AbstractViewItemDropTarget> create_drop_target() const;
 
   /** Get the view this item is registered for using #AbstractView::register_item(). */
   AbstractView &get_view() const;
@@ -200,7 +227,7 @@ template<typename ToType> ToType *AbstractViewItem::from_item_handle(uiViewItemH
  * \{ */
 
 /**
- * Class to enable dragging a view item. An item can return a drop controller for itself by
+ * Class to enable dragging a view item. An item can return a drag controller for itself by
  * implementing #AbstractViewItem::create_drag_controller().
  */
 class AbstractViewItemDragController {
@@ -222,38 +249,15 @@ class AbstractViewItemDragController {
 
 /**
  * Class to define the behavior when dropping something onto/into a view item, plus the behavior
- * when dragging over this item. An item can return a drop controller for itself via a custom
+ * when dragging over this item. An item can return a drop target for itself via a custom
- * implementation of #AbstractViewItem::create_drop_controller().
+ * implementation of #AbstractViewItem::create_drop_target().
  */
-class AbstractViewItemDropController {
+class AbstractViewItemDropTarget : public DropTargetInterface {
  protected:
   AbstractView &view_;
 
  public:
-  AbstractViewItemDropController(AbstractView &view);
+  AbstractViewItemDropTarget(AbstractView &view);
-  virtual ~AbstractViewItemDropController() = default;
-
-  /**
-   * Check if the data dragged with \a drag can be dropped on the item this controller is for.
-   * \param r_disabled_hint: Return a static string to display to the user, explaining why dropping
-   *                         isn't possible on this item. Shouldn't be done too aggressively, e.g.
-   *                         don't set this if the drag-type can't be dropped here; only if it can
-   *                         but there's another reason it can't be dropped.
-   *                         Can assume this is a non-null pointer.
-   */
-  virtual bool can_drop(const wmDrag &drag, const char **r_disabled_hint) const = 0;
-  /**
-   * Custom text to display when dragging over a view item. Should explain what happens when
-   * dropping the data onto this item. Will only be used if #AbstractViewItem::can_drop()
-   * returns true, so the implementing override doesn't have to check that again.
-   * The returned value must be a translated string.
-   */
-  virtual std::string drop_tooltip(const wmDrag &drag) const = 0;
-  /**
-   * Execute the logic to apply a drop of the data dragged with \a drag onto/into the item this
-   * controller is for.
-   */
-  virtual bool on_drop(struct bContext *C, const wmDrag &drag) = 0;
 
   /** Request the view the item is registered for as type #ViewType. Throws a `std::bad_cast`
    * exception if the view is not of the requested type. */
@@ -267,7 +271,7 @@ template<class ViewType> ViewType &AbstractViewItemDragController::get_view() co
   return dynamic_cast<ViewType &>(view_);
 }
 
-template<class ViewType> ViewType &AbstractViewItemDropController::get_view() const
+template<class ViewType> ViewType &AbstractViewItemDropTarget::get_view() const
 {
   static_assert(std::is_base_of<AbstractView, ViewType>::value,
                 "Type must derive from and implement the ui::AbstractView interface");

source/blender/editors/include/UI_interface.h

@@ -3274,18 +3274,12 @@ void UI_view_item_context_menu_build(struct bContext *C,
  * \return True if dragging started successfully, otherwise false.
  */
 bool UI_view_item_drag_start(struct bContext *C, const uiViewItemHandle *item_);
-bool UI_view_item_can_drop(const uiViewItemHandle *item_,
-                           const struct wmDrag *drag,
-                           const char **r_disabled_hint);
-char *UI_view_item_drop_tooltip(const uiViewItemHandle *item, const struct wmDrag *drag);
-/**
- * Let a view item handle a drop event.
- * \return True if the drop was handled by the view item.
- */
-bool UI_view_item_drop_handle(struct bContext *C,
-                              const uiViewItemHandle *item_,
-                              const struct ListBase *drags);
 
+/**
+ * \param xy: Coordinate to find a view item at, in window space.
+ * \param pad: Extra padding added to the bounding box of the view.
+ */
+uiViewHandle *UI_region_view_find_at(const struct ARegion *region, const int xy[2], int pad);
 /**
  * \param xy: Coordinate to find a view item at, in window space.
  */

source/blender/editors/include/UI_interface.hh

@@ -18,11 +18,17 @@ namespace blender::nodes::geo_eval_log {
 struct GeometryAttributeInfo;
 }
 
+struct ARegion;
+struct bContext;
 struct PointerRNA;
 struct StructRNA;
 struct uiBlock;
+struct uiLayout;
 struct uiList;
 struct uiSearchItems;
+struct uiViewHandle;
+struct uiViewItemHandle;
+struct wmDrag;
 
 namespace blender::ui {
 
@@ -54,6 +60,67 @@ void attribute_search_add_items(StringRefNull str,
                                 uiSearchItems *items,
                                 bool is_first);
 
+/**
+ * This provides a common interface for UI elements that want to support dragging & dropping
+ * entities into/onto them. With it, the element can determine if the dragged entity can be dropped
+ * onto itself, provide feedback while dragging and run custom code for the dropping.
+ *
+ * Note that this is just an interface. A #wmDropBox is needed to request instances of it from a UI
+ * element and call its functions. For example the drop box using "UI_OT_view_drop" implements
+ * dropping for views and view items via this interface. To support other kinds of UI elements,
+ * similar drop boxes would be necessary.
+ */
+class DropTargetInterface {
+ public:
+  DropTargetInterface() = default;
+  virtual ~DropTargetInterface() = default;
+
+  /**
+   * Check if the data dragged with \a drag can be dropped on the element this drop target is for.
+   * \param r_disabled_hint: Return a static string to display to the user, explaining why dropping
+   *                         isn't possible on this UI element. Shouldn't be done too aggressively,
+   *                         e.g. don't set this if the drag-type can't be dropped here; only if it
+   *                         can but there's another reason it can't be dropped. Can assume this is
+   *                         a non-null pointer.
+   */
+  virtual bool can_drop(const wmDrag &drag, const char **r_disabled_hint) const = 0;
+  /**
+   * Custom text to display when dragging over the element using this drop target. Should
+   * explain what happens when dropping the data onto this UI element. Will only be used if
+   * #DropTargetInterface::can_drop() returns true, so the implementing override doesn't have
+   * to check that again. The returned value must be a translated string.
+   */
+  virtual std::string drop_tooltip(const wmDrag &drag) const = 0;
+  /**
+   * Execute the logic to apply a drop of the data dragged with \a drag onto/into the UI element
+   * this drop target is for.
+   */
+  virtual bool on_drop(bContext *C, const wmDrag &drag) const = 0;
+};
+
+/**
+ * Let a drop target handle a drop event.
+ * \return True if the dropping was successful.
+ */
+bool drop_target_apply_drop(bContext &C,
+                            const DropTargetInterface &drop_target,
+                            const ListBase &drags);
+/**
+ * Call #DropTargetInterface::drop_tooltip() and return the result as newly allocated C string
+ * (unless the result is empty, returns null then). Needs freeing with MEM_freeN().
+ */
+char *drop_target_tooltip(const DropTargetInterface &drop_target, const wmDrag &drag);
+
+std::unique_ptr<DropTargetInterface> view_drop_target(const uiViewHandle *view_handle);
+std::unique_ptr<DropTargetInterface> view_item_drop_target(const uiViewItemHandle *item_handle);
+/**
+ * Try to find a view item with a drop target under the mouse cursor, or if not found, a view
+ * with a drop target.
+ * \param xy: Coordinate to find a drop target at, in window space.
+ */
+std::unique_ptr<DropTargetInterface> region_views_find_drop_target_at(const ARegion *region,
+                                                                      const int xy[2]);
+
 }  // namespace blender::ui
 
 enum eUIListFilterResult {

source/blender/editors/interface/CMakeLists.txt

@@ -46,6 +46,7 @@ set(SRC
   interface_context_path.cc
   interface_drag.cc
   interface_draw.cc
+  interface_drop.cc
   interface_dropboxes.cc
   interface_handlers.cc
   interface_icons.cc

source/blender/editors/interface/interface.cc

@@ -2014,6 +2014,8 @@ void UI_block_end_ex(const bContext *C, uiBlock *block, const int xy[2], int r_x
       break;
   }
 
+  ui_block_views_bounds_calc(block);
+
   if (block->rect.xmin == 0.0f && block->rect.xmax == 0.0f) {
     UI_block_bounds_set_normal(block, 0);
   }

source/blender/editors/interface/interface_drop.cc

@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup edinterface
+ */
+
+#include "UI_interface.hh"
+
+namespace blender::ui {
+
+bool drop_target_apply_drop(bContext &C,
+                            const DropTargetInterface &drop_target,
+                            const ListBase &drags)
+{
+
+  const char *disabled_hint_dummy = nullptr;
+  LISTBASE_FOREACH (const wmDrag *, drag, &drags) {
+    if (drop_target.can_drop(*drag, &disabled_hint_dummy)) {
+      return drop_target.on_drop(&C, *drag);
+    }
+  }
+
+  return false;
+}
+
+char *drop_target_tooltip(const DropTargetInterface &drop_target, const wmDrag &drag)
+{
+  const std::string tooltip = drop_target.drop_tooltip(drag);
+  return tooltip.empty() ? nullptr : BLI_strdup(tooltip.c_str());
+}
+
+}  // namespace blender::ui

source/blender/editors/interface/interface_dropboxes.cc

@@ -20,6 +20,9 @@
 #include "WM_api.h"
 
 #include "UI_interface.h"
+#include "UI_interface.hh"
+
+using namespace blender::ui;
 
 /* -------------------------------------------------------------------- */
 /** \name View Drag/Drop Callbacks
@@ -28,28 +31,28 @@
 static bool ui_view_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
 {
   const ARegion *region = CTX_wm_region(C);
-  const uiViewItemHandle *hovered_item = UI_region_views_find_item_at(region, event->xy);
+
-  if (!hovered_item) {
+  std::unique_ptr<DropTargetInterface> drop_target = region_views_find_drop_target_at(
+      region, event->xy);
+  if (!drop_target) {
     return false;
   }
 
   if (drag->drop_state.free_disabled_info) {
     MEM_SAFE_FREE(drag->drop_state.disabled_info);
   }
-
   drag->drop_state.free_disabled_info = false;
-  return UI_view_item_can_drop(hovered_item, drag, &drag->drop_state.disabled_info);
+
+  return drop_target->can_drop(*drag, &drag->drop_state.disabled_info);
 }
 
 static char *ui_view_drop_tooltip(bContext *C, wmDrag *drag, const int xy[2], wmDropBox * /*drop*/)
 {
   const ARegion *region = CTX_wm_region(C);
-  const uiViewItemHandle *hovered_item = UI_region_views_find_item_at(region, xy);
+  std::unique_ptr<DropTargetInterface> drop_target = region_views_find_drop_target_at(region,
-  if (!hovered_item) {
+                                                                                         xy);
-    return nullptr;
-  }
 
-  return UI_view_item_drop_tooltip(hovered_item, drag);
+  return drop_target_tooltip(*drop_target, *drag);
 }
 
 /** \} */

source/blender/editors/interface/interface_intern.hh

@@ -1452,6 +1452,7 @@ void ui_interface_tag_script_reload_queries();
 /* interface_view.cc */
 
 void ui_block_free_views(uiBlock *block);
+void ui_block_views_bounds_calc(const uiBlock *block);
 void ui_block_views_listen(const uiBlock *block, const wmRegionListenerParams *listener_params);
 uiViewHandle *ui_block_view_find_matching_in_old_block(const uiBlock *new_block,
                                                        const uiViewHandle *new_view);

source/blender/editors/interface/interface_ops.cc

@@ -47,6 +47,7 @@
 #include "RNA_types.h"
 
 #include "UI_interface.h"
+#include "UI_interface.hh"
 
 #include "interface_intern.hh"
 
@@ -65,6 +66,8 @@
 #include "ED_screen.h"
 #include "ED_text.h"
 
+using namespace blender::ui;
+
 /* -------------------------------------------------------------------- */
 /** \name Immediate redraw helper
  *
@@ -2351,7 +2354,7 @@ static void UI_OT_list_start_filter(wmOperatorType *ot)
 /** \} */
 
 /* -------------------------------------------------------------------- */
-/** \name UI Tree-View Drop Operator
+/** \name UI View Drop Operator
  * \{ */
 
 static bool ui_view_drop_poll(bContext *C)
@@ -2361,9 +2364,7 @@ static bool ui_view_drop_poll(bContext *C)
   if (region == nullptr) {
     return false;
   }
-  const uiViewItemHandle *hovered_item = UI_region_views_find_item_at(region, win->eventstate->xy);
+  return region_views_find_drop_target_at(region, win->eventstate->xy) != nullptr;
-
-  return hovered_item != nullptr;
 }
 
 static int ui_view_drop_invoke(bContext *C, wmOperator * /*op*/, const wmEvent *event)
@@ -2373,10 +2374,11 @@ static int ui_view_drop_invoke(bContext *C, wmOperator * /*op*/, const wmEvent *
   }
 
   const ARegion *region = CTX_wm_region(C);
-  uiViewItemHandle *hovered_item = UI_region_views_find_item_at(region, event->xy);
+  std::unique_ptr<DropTargetInterface> drop_target = region_views_find_drop_target_at(
+      region, event->xy);
 
-  if (!UI_view_item_drop_handle(
+  if (!drop_target_apply_drop(
-          C, hovered_item, static_cast<const ListBase *>(event->customdata))) {
+          *C, *drop_target, *static_cast<const ListBase *>(event->customdata))) {
     return OPERATOR_CANCELLED | OPERATOR_PASS_THROUGH;
   }
 
@@ -2385,9 +2387,9 @@ static int ui_view_drop_invoke(bContext *C, wmOperator * /*op*/, const wmEvent *
 
 static void UI_OT_view_drop(wmOperatorType *ot)
 {
-  ot->name = "View drop";
+  ot->name = "View Drop";
   ot->idname = "UI_OT_view_drop";
-  ot->description = "Drag and drop items onto a data-set item";
+  ot->description = "Drag and drop onto a data-set or item within the data-set";
 
   ot->invoke = ui_view_drop_invoke;
   ot->poll = ui_view_drop_poll;

source/blender/editors/interface/views/abstract_view.cc

@@ -62,6 +62,12 @@ void AbstractView::update_from_old(uiBlock &new_block)
 /** \name Default implementations of virtual functions
  * \{ */
 
+std::unique_ptr<AbstractViewDropTarget> AbstractView::create_drop_target() const
+{
+  /* There's no drop target (and hence no drop support) by default. */
+  return nullptr;
+}
+
 bool AbstractView::listen(const wmNotifier & /*notifier*/) const
 {
   /* Nothing by default. */
@@ -104,6 +110,23 @@ MutableSpan<char> AbstractView::get_rename_buffer()
   return *rename_buffer_;
 }
 
+std::optional<rcti> AbstractView::get_bounds() const
+{
+  return bounds_;
+}
+
+/** \} */
+
+/* ---------------------------------------------------------------------- */
+/** \name General API functions
+ * \{ */
+
+std::unique_ptr<DropTargetInterface> view_drop_target(const uiViewHandle *view_handle)
+{
+  const AbstractView &view = reinterpret_cast<const AbstractView &>(*view_handle);
+  return view.create_drop_target();
+}
+
 /** \} */
 
 }  // namespace blender::ui

source/blender/editors/interface/views/abstract_view_item.cc

@@ -174,9 +174,9 @@ std::unique_ptr<AbstractViewItemDragController> AbstractViewItem::create_drag_co
   return nullptr;
 }
 
-std::unique_ptr<AbstractViewItemDropController> AbstractViewItem::create_drop_controller() const
+std::unique_ptr<AbstractViewItemDropTarget> AbstractViewItem::create_drop_target() const
 {
-  /* There's no drop controller (and hence no drop support) by default. */
+  /* There's no drop target (and hence no drop support) by default. */
   return nullptr;
 }
 
@@ -189,7 +189,7 @@ void AbstractViewItemDragController::on_drag_start()
   /* Do nothing by default. */
 }
 
-AbstractViewItemDropController::AbstractViewItemDropController(AbstractView &view) : view_(view)
+AbstractViewItemDropTarget::AbstractViewItemDropTarget(AbstractView &view) : view_(view)
 {
 }
 
@@ -217,6 +217,18 @@ bool AbstractViewItem::is_active() const
 
 /** \} */
 
+/* ---------------------------------------------------------------------- */
+/** \name General API functions
+ * \{ */
+
+std::unique_ptr<DropTargetInterface> view_item_drop_target(const uiViewItemHandle *item_handle)
+{
+  const AbstractViewItem &item = reinterpret_cast<const AbstractViewItem &>(*item_handle);
+  return item.create_drop_target();
+}
+
+/** \} */
+
 }  // namespace blender::ui
 
 /* ---------------------------------------------------------------------- */
@@ -264,45 +276,6 @@ class ViewItemAPIWrapper {
 
     return true;
   }
-
-  static bool can_drop(const AbstractViewItem &item,
-                       const wmDrag &drag,
-                       const char **r_disabled_hint)
-  {
-    const std::unique_ptr<AbstractViewItemDropController> drop_controller =
-        item.create_drop_controller();
-    if (!drop_controller) {
-      return false;
-    }
-
-    return drop_controller->can_drop(drag, r_disabled_hint);
-  }
-
-  static std::string drop_tooltip(const AbstractViewItem &item, const wmDrag &drag)
-  {
-    const std::unique_ptr<AbstractViewItemDropController> drop_controller =
-        item.create_drop_controller();
-    if (!drop_controller) {
-      return {};
-    }
-
-    return drop_controller->drop_tooltip(drag);
-  }
-
-  static bool drop_handle(bContext &C, const AbstractViewItem &item, const ListBase &drags)
-  {
-    std::unique_ptr<AbstractViewItemDropController> drop_controller =
-        item.create_drop_controller();
-
-    const char *disabled_hint_dummy = nullptr;
-    LISTBASE_FOREACH (const wmDrag *, drag, &drags) {
-      if (drop_controller->can_drop(*drag, &disabled_hint_dummy)) {
-        return drop_controller->on_drop(&C, *drag);
-      }
-    }
-
-    return false;
-  }
 };
 
 }  // namespace blender::ui
@@ -348,26 +321,4 @@ bool UI_view_item_drag_start(bContext *C, const uiViewItemHandle *item_)
   return ViewItemAPIWrapper::drag_start(*C, item);
 }
 
-bool UI_view_item_can_drop(const uiViewItemHandle *item_,
-                           const wmDrag *drag,
-                           const char **r_disabled_hint)
-{
-  const AbstractViewItem &item = reinterpret_cast<const AbstractViewItem &>(*item_);
-  return ViewItemAPIWrapper::can_drop(item, *drag, r_disabled_hint);
-}
-
-char *UI_view_item_drop_tooltip(const uiViewItemHandle *item_, const wmDrag *drag)
-{
-  const AbstractViewItem &item = reinterpret_cast<const AbstractViewItem &>(*item_);
-
-  const std::string tooltip = ViewItemAPIWrapper::drop_tooltip(item, *drag);
-  return tooltip.empty() ? nullptr : BLI_strdup(tooltip.c_str());
-}
-
-bool UI_view_item_drop_handle(bContext *C, const uiViewItemHandle *item_, const ListBase *drags)
-{
-  const AbstractViewItem &item = reinterpret_cast<const AbstractViewItem &>(*item_);
-  return ViewItemAPIWrapper::drop_handle(*C, item, *drags);
-}
-
 /** \} */

source/blender/editors/interface/views/interface_view.cc

@@ -24,6 +24,7 @@
 #include "BKE_screen.h"
 
 #include "BLI_listbase.h"
+#include "BLI_map.hh"
 
 #include "ED_screen.h"
 
@@ -44,6 +45,8 @@ using namespace blender::ui;
 struct ViewLink : public Link {
   std::string idname;
   std::unique_ptr<AbstractView> view;
+
+  static void views_bounds_calc(const uiBlock &block);
 };
 
 template<class T>
@@ -81,6 +84,51 @@ void ui_block_free_views(uiBlock *block)
   }
 }
 
+void ViewLink::views_bounds_calc(const uiBlock &block)
+{
+  Map<AbstractView *, rcti> views_bounds;
+
+  rcti minmax;
+  BLI_rcti_init_minmax(&minmax);
+  LISTBASE_FOREACH (ViewLink *, link, &block.views) {
+    views_bounds.add(link->view.get(), minmax);
+  }
+
+  LISTBASE_FOREACH (uiBut *, but, &block.buttons) {
+    if (but->type != UI_BTYPE_VIEW_ITEM) {
+      continue;
+    }
+    uiButViewItem *view_item_but = static_cast<uiButViewItem *>(but);
+    if (!view_item_but->view_item) {
+      continue;
+    }
+
+    /* Get the view from the button. */
+    AbstractViewItem &view_item = reinterpret_cast<AbstractViewItem &>(*view_item_but->view_item);
+    AbstractView &view = view_item.get_view();
+
+    rcti &bounds = views_bounds.lookup(&view);
+    rcti but_rcti{};
+    BLI_rcti_rctf_copy_round(&but_rcti, &view_item_but->rect);
+    BLI_rcti_do_minmax_rcti(&bounds, &but_rcti);
+  }
+
+  for (const auto item : views_bounds.items()) {
+    const rcti &bounds = item.value;
+    if (BLI_rcti_is_empty(&bounds)) {
+      continue;
+    }
+
+    AbstractView &view = *item.key;
+    view.bounds_ = bounds;
+  }
+}
+
+void ui_block_views_bounds_calc(const uiBlock *block)
+{
+  ViewLink::views_bounds_calc(*block);
+}
+
 void ui_block_views_listen(const uiBlock *block, const wmRegionListenerParams *listener_params)
 {
   ARegion *region = listener_params->region;
@@ -92,6 +140,35 @@ void ui_block_views_listen(const uiBlock *block, const wmRegionListenerParams *l
   }
 }
 
+/* Similar to #ui_but_find_mouse_over_ex(). */
+uiViewHandle *UI_region_view_find_at(const ARegion *region, const int xy[2], const int pad)
+{
+  if (!ui_region_contains_point_px(region, xy)) {
+    return nullptr;
+  }
+  LISTBASE_FOREACH (uiBlock *, block, &region->uiblocks) {
+    float mx = xy[0], my = xy[1];
+    ui_window_to_block_fl(region, block, &mx, &my);
+
+    LISTBASE_FOREACH (ViewLink *, view_link, &block->views) {
+      std::optional<rcti> bounds = view_link->view->get_bounds();
+      if (!bounds) {
+        continue;
+      }
+
+      rcti padded_bounds = *bounds;
+      if (pad) {
+        BLI_rcti_pad(&padded_bounds, pad, pad);
+      }
+      if (BLI_rcti_isect_pt(&padded_bounds, mx, my)) {
+        return reinterpret_cast<uiViewHandle *>(view_link->view.get());
+      }
+    }
+  }
+
+  return nullptr;
+}
+
 uiViewItemHandle *UI_region_views_find_item_at(const ARegion *region, const int xy[2])
 {
   uiButViewItem *item_but = (uiButViewItem *)ui_view_item_find_mouse_over(region, xy);
@@ -112,6 +189,34 @@ uiViewItemHandle *UI_region_views_find_active_item(const ARegion *region)
   return item_but->view_item;
 }
 
+namespace blender::ui {
+
+std::unique_ptr<DropTargetInterface> region_views_find_drop_target_at(const ARegion *region,
+                                                                      const int xy[2])
+{
+  const uiViewItemHandle *hovered_view_item = UI_region_views_find_item_at(region, xy);
+  if (hovered_view_item) {
+    std::unique_ptr<DropTargetInterface> drop_target = view_item_drop_target(hovered_view_item);
+    if (drop_target) {
+      return drop_target;
+    }
+  }
+
+  /* Get style for some sensible padding around the view items. */
+  const uiStyle *style = UI_style_get_dpi();
+  const uiViewHandle *hovered_view = UI_region_view_find_at(region, xy, style->buttonspacex);
+  if (hovered_view) {
+    std::unique_ptr<DropTargetInterface> drop_target = view_drop_target(hovered_view);
+    if (drop_target) {
+      return drop_target;
+    }
+  }
+
+  return nullptr;
+}
+
+}  // namespace blender::ui
+
 static StringRef ui_block_view_find_idname(const uiBlock &block, const AbstractView &view)
 {
   /* First get the idname the of the view we're looking for. */

source/blender/editors/space_file/asset_catalog_tree_view.cc

@@ -49,7 +49,7 @@ class AssetCatalogTreeView : public ui::AbstractTreeView {
   SpaceFile &space_file_;
 
   friend class AssetCatalogTreeViewItem;
-  friend class AssetCatalogDropController;
+  friend class AssetCatalogDropTarget;
   friend class AssetCatalogTreeViewAllItem;
 
  public:
@@ -90,7 +90,7 @@ class AssetCatalogTreeViewItem : public ui::BasicTreeViewItem {
   /** Add drag support for catalog items. */
   std::unique_ptr<ui::AbstractViewItemDragController> create_drag_controller() const override;
   /** Add dropping support for catalog items. */
-  std::unique_ptr<ui::AbstractViewItemDropController> create_drop_controller() const override;
+  std::unique_ptr<ui::AbstractViewItemDropTarget> create_drop_target() const override;
 };
 
 class AssetCatalogDragController : public ui::AbstractViewItemDragController {
@@ -105,15 +105,15 @@ class AssetCatalogDragController : public ui::AbstractViewItemDragController {
   void on_drag_start() override;
 };
 
-class AssetCatalogDropController : public ui::AbstractViewItemDropController {
+class AssetCatalogDropTarget : public ui::AbstractViewItemDropTarget {
   AssetCatalogTreeItem &catalog_item_;
 
  public:
-  AssetCatalogDropController(AssetCatalogTreeView &tree_view, AssetCatalogTreeItem &catalog_item);
+  AssetCatalogDropTarget(AssetCatalogTreeView &tree_view, AssetCatalogTreeItem &catalog_item);
 
   bool can_drop(const wmDrag &drag, const char **r_disabled_hint) const override;
   std::string drop_tooltip(const wmDrag &drag) const override;
-  bool on_drop(struct bContext *C, const wmDrag &drag) override;
+  bool on_drop(struct bContext *C, const wmDrag &drag) const override;
 
   ::AssetLibrary &get_asset_library() const;
 
@@ -146,29 +146,29 @@ class AssetCatalogTreeViewAllItem : public ui::BasicTreeViewItem {
 
   void build_row(uiLayout &row) override;
 
-  struct DropController : public ui::AbstractViewItemDropController {
+  struct DropTarget : public ui::AbstractViewItemDropTarget {
-    DropController(AssetCatalogTreeView &tree_view);
+    DropTarget(AssetCatalogTreeView &tree_view);
 
     bool can_drop(const wmDrag &drag, const char **r_disabled_hint) const override;
     std::string drop_tooltip(const wmDrag &drag) const override;
-    bool on_drop(struct bContext *C, const wmDrag &drag) override;
+    bool on_drop(struct bContext *C, const wmDrag &drag) const override;
   };
 
-  std::unique_ptr<ui::AbstractViewItemDropController> create_drop_controller() const override;
+  std::unique_ptr<ui::AbstractViewItemDropTarget> create_drop_target() const override;
 };
 
 class AssetCatalogTreeViewUnassignedItem : public ui::BasicTreeViewItem {
   using BasicTreeViewItem::BasicTreeViewItem;
 
-  struct DropController : public ui::AbstractViewItemDropController {
+  struct DropTarget : public ui::AbstractViewItemDropTarget {
-    DropController(AssetCatalogTreeView &tree_view);
+    DropTarget(AssetCatalogTreeView &tree_view);
 
     bool can_drop(const wmDrag &drag, const char **r_disabled_hint) const override;
     std::string drop_tooltip(const wmDrag &drag) const override;
-    bool on_drop(struct bContext *C, const wmDrag &drag) override;
+    bool on_drop(struct bContext *C, const wmDrag &drag) const override;
   };
 
-  std::unique_ptr<ui::AbstractViewItemDropController> create_drop_controller() const override;
+  std::unique_ptr<ui::AbstractViewItemDropTarget> create_drop_target() const override;
 };
 
 /* ---------------------------------------------------------------------- */
@@ -339,10 +339,10 @@ bool AssetCatalogTreeViewItem::rename(StringRefNull new_name)
   return true;
 }
 
-std::unique_ptr<ui::AbstractViewItemDropController> AssetCatalogTreeViewItem::
+std::unique_ptr<ui::AbstractViewItemDropTarget> AssetCatalogTreeViewItem::create_drop_target()
-    create_drop_controller() const
+    const
 {
-  return std::make_unique<AssetCatalogDropController>(
+  return std::make_unique<AssetCatalogDropTarget>(
       static_cast<AssetCatalogTreeView &>(get_tree_view()), catalog_item_);
 }
 
@@ -355,13 +355,13 @@ std::unique_ptr<ui::AbstractViewItemDragController> AssetCatalogTreeViewItem::
 
 /* ---------------------------------------------------------------------- */
 
-AssetCatalogDropController::AssetCatalogDropController(AssetCatalogTreeView &tree_view,
+AssetCatalogDropTarget::AssetCatalogDropTarget(AssetCatalogTreeView &tree_view,
-                                                       AssetCatalogTreeItem &catalog_item)
+                                               AssetCatalogTreeItem &catalog_item)
-    : ui::AbstractViewItemDropController(tree_view), catalog_item_(catalog_item)
+    : ui::AbstractViewItemDropTarget(tree_view), catalog_item_(catalog_item)
 {
 }
 
-bool AssetCatalogDropController::can_drop(const wmDrag &drag, const char **r_disabled_hint) const
+bool AssetCatalogDropTarget::can_drop(const wmDrag &drag, const char **r_disabled_hint) const
 {
   if (drag.type == WM_DRAG_ASSET_CATALOG) {
     const ::AssetLibrary &library = get_asset_library();
@@ -389,7 +389,7 @@ bool AssetCatalogDropController::can_drop(const wmDrag &drag, const char **r_dis
   return false;
 }
 
-std::string AssetCatalogDropController::drop_tooltip(const wmDrag &drag) const
+std::string AssetCatalogDropTarget::drop_tooltip(const wmDrag &drag) const
 {
   if (drag.type == WM_DRAG_ASSET_CATALOG) {
     return drop_tooltip_asset_catalog(drag);
@@ -397,7 +397,7 @@ std::string AssetCatalogDropController::drop_tooltip(const wmDrag &drag) const
   return drop_tooltip_asset_list(drag);
 }
 
-std::string AssetCatalogDropController::drop_tooltip_asset_catalog(const wmDrag &drag) const
+std::string AssetCatalogDropTarget::drop_tooltip_asset_catalog(const wmDrag &drag) const
 {
   BLI_assert(drag.type == WM_DRAG_ASSET_CATALOG);
   const AssetCatalog *src_catalog = get_drag_catalog(drag, get_asset_library());
@@ -406,7 +406,7 @@ std::string AssetCatalogDropController::drop_tooltip_asset_catalog(const wmDrag
          TIP_("into") + " '" + catalog_item_.get_name() + "'";
 }
 
-std::string AssetCatalogDropController::drop_tooltip_asset_list(const wmDrag &drag) const
+std::string AssetCatalogDropTarget::drop_tooltip_asset_list(const wmDrag &drag) const
 {
   BLI_assert(drag.type == WM_DRAG_ASSET_LIST);
 
@@ -429,7 +429,7 @@ std::string AssetCatalogDropController::drop_tooltip_asset_list(const wmDrag &dr
   return basic_tip;
 }
 
-bool AssetCatalogDropController::on_drop(struct bContext *C, const wmDrag &drag)
+bool AssetCatalogDropTarget::on_drop(struct bContext *C, const wmDrag &drag) const
 {
   if (drag.type == WM_DRAG_ASSET_CATALOG) {
     return drop_asset_catalog_into_catalog(
@@ -442,7 +442,7 @@ bool AssetCatalogDropController::on_drop(struct bContext *C, const wmDrag &drag)
                                   catalog_item_.get_simple_name());
 }
 
-bool AssetCatalogDropController::drop_asset_catalog_into_catalog(
+bool AssetCatalogDropTarget::drop_asset_catalog_into_catalog(
     const wmDrag &drag,
     AssetCatalogTreeView &tree_view,
     const std::optional<CatalogID> drop_catalog_id)
@@ -456,11 +456,11 @@ bool AssetCatalogDropController::drop_asset_catalog_into_catalog(
   return true;
 }
 
-bool AssetCatalogDropController::drop_assets_into_catalog(struct bContext *C,
+bool AssetCatalogDropTarget::drop_assets_into_catalog(struct bContext *C,
-                                                          const AssetCatalogTreeView &tree_view,
+                                                      const AssetCatalogTreeView &tree_view,
-                                                          const wmDrag &drag,
+                                                      const wmDrag &drag,
-                                                          CatalogID catalog_id,
+                                                      CatalogID catalog_id,
-                                                          StringRefNull simple_name)
+                                                      StringRefNull simple_name)
 {
   BLI_assert(drag.type == WM_DRAG_ASSET_LIST);
   const ListBase *asset_drags = WM_drag_asset_list_get(&drag);
@@ -491,8 +491,8 @@ bool AssetCatalogDropController::drop_assets_into_catalog(struct bContext *C,
   return true;
 }
 
-AssetCatalog *AssetCatalogDropController::get_drag_catalog(const wmDrag &drag,
+AssetCatalog *AssetCatalogDropTarget::get_drag_catalog(const wmDrag &drag,
-                                                           const ::AssetLibrary &asset_library)
+                                                       const ::AssetLibrary &asset_library)
 {
   if (drag.type != WM_DRAG_ASSET_CATALOG) {
     return nullptr;
@@ -504,8 +504,7 @@ AssetCatalog *AssetCatalogDropController::get_drag_catalog(const wmDrag &drag,
   return catalog_service->find_catalog(catalog_drag->drag_catalog_id);
 }
 
-bool AssetCatalogDropController::has_droppable_asset(const wmDrag &drag,
+bool AssetCatalogDropTarget::has_droppable_asset(const wmDrag &drag, const char **r_disabled_hint)
-                                                     const char **r_disabled_hint)
 {
   const ListBase *asset_drags = WM_drag_asset_list_get(&drag);
 
@@ -521,8 +520,8 @@ bool AssetCatalogDropController::has_droppable_asset(const wmDrag &drag,
   return false;
 }
 
-bool AssetCatalogDropController::can_modify_catalogs(const ::AssetLibrary &library,
+bool AssetCatalogDropTarget::can_modify_catalogs(const ::AssetLibrary &library,
-                                                     const char **r_disabled_hint)
+                                                 const char **r_disabled_hint)
 {
   if (ED_asset_catalogs_read_only(library)) {
     *r_disabled_hint = "Catalogs cannot be edited in this asset library";
@@ -531,7 +530,7 @@ bool AssetCatalogDropController::can_modify_catalogs(const ::AssetLibrary &libra
   return true;
 }
 
-::AssetLibrary &AssetCatalogDropController::get_asset_library() const
+::AssetLibrary &AssetCatalogDropTarget::get_asset_library() const
 {
   return *get_view<AssetCatalogTreeView>().asset_library_;
 }
@@ -580,30 +579,30 @@ void AssetCatalogTreeViewAllItem::build_row(uiLayout &row)
   RNA_string_set(props, "parent_path", nullptr);
 }
 
-std::unique_ptr<ui::AbstractViewItemDropController> AssetCatalogTreeViewAllItem::
+std::unique_ptr<ui::AbstractViewItemDropTarget> AssetCatalogTreeViewAllItem::create_drop_target()
-    create_drop_controller() const
+    const
 {
-  return std::make_unique<AssetCatalogTreeViewAllItem::DropController>(
+  return std::make_unique<AssetCatalogTreeViewAllItem::DropTarget>(
       static_cast<AssetCatalogTreeView &>(get_tree_view()));
 }
 
-AssetCatalogTreeViewAllItem::DropController::DropController(AssetCatalogTreeView &tree_view)
+AssetCatalogTreeViewAllItem::DropTarget::DropTarget(AssetCatalogTreeView &tree_view)
-    : ui::AbstractViewItemDropController(tree_view)
+    : ui::AbstractViewItemDropTarget(tree_view)
 {
 }
 
-bool AssetCatalogTreeViewAllItem::DropController::can_drop(const wmDrag &drag,
+bool AssetCatalogTreeViewAllItem::DropTarget::can_drop(const wmDrag &drag,
-                                                           const char **r_disabled_hint) const
+                                                       const char **r_disabled_hint) const
 {
   if (drag.type != WM_DRAG_ASSET_CATALOG) {
     return false;
   }
   ::AssetLibrary &library = *get_view<AssetCatalogTreeView>().asset_library_;
-  if (!AssetCatalogDropController::can_modify_catalogs(library, r_disabled_hint)) {
+  if (!AssetCatalogDropTarget::can_modify_catalogs(library, r_disabled_hint)) {
     return false;
   }
 
-  const AssetCatalog *drag_catalog = AssetCatalogDropController::get_drag_catalog(drag, library);
+  const AssetCatalog *drag_catalog = AssetCatalogDropTarget::get_drag_catalog(drag, library);
   if (drag_catalog->path.parent() == "") {
     *r_disabled_hint = "Catalog is already placed at the highest level";
     return false;
@@ -612,21 +611,21 @@ bool AssetCatalogTreeViewAllItem::DropController::can_drop(const wmDrag &drag,
   return true;
 }
 
-std::string AssetCatalogTreeViewAllItem::DropController::drop_tooltip(const wmDrag &drag) const
+std::string AssetCatalogTreeViewAllItem::DropTarget::drop_tooltip(const wmDrag &drag) const
 {
   BLI_assert(drag.type == WM_DRAG_ASSET_CATALOG);
-  const AssetCatalog *drag_catalog = AssetCatalogDropController::get_drag_catalog(
+  const AssetCatalog *drag_catalog = AssetCatalogDropTarget::get_drag_catalog(
       drag, *get_view<AssetCatalogTreeView>().asset_library_);
 
   return std::string(TIP_("Move Catalog")) + " '" + drag_catalog->path.name() + "' " +
          TIP_("to the top level of the tree");
 }
 
-bool AssetCatalogTreeViewAllItem::DropController::on_drop(struct bContext * /*C*/,
+bool AssetCatalogTreeViewAllItem::DropTarget::on_drop(struct bContext * /*C*/,
-                                                          const wmDrag &drag)
+                                                      const wmDrag &drag) const
 {
   BLI_assert(drag.type == WM_DRAG_ASSET_CATALOG);
-  return AssetCatalogDropController::drop_asset_catalog_into_catalog(
+  return AssetCatalogDropTarget::drop_asset_catalog_into_catalog(
       drag,
       get_view<AssetCatalogTreeView>(),
       /* No value to drop into the root level. */
@@ -635,29 +634,28 @@ bool AssetCatalogTreeViewAllItem::DropController::on_drop(struct bContext * /*C*
 
 /* ---------------------------------------------------------------------- */
 
-std::unique_ptr<ui::AbstractViewItemDropController> AssetCatalogTreeViewUnassignedItem::
+std::unique_ptr<ui::AbstractViewItemDropTarget> AssetCatalogTreeViewUnassignedItem::
-    create_drop_controller() const
+    create_drop_target() const
 {
-  return std::make_unique<AssetCatalogTreeViewUnassignedItem::DropController>(
+  return std::make_unique<AssetCatalogTreeViewUnassignedItem::DropTarget>(
       static_cast<AssetCatalogTreeView &>(get_tree_view()));
 }
 
-AssetCatalogTreeViewUnassignedItem::DropController::DropController(AssetCatalogTreeView &tree_view)
+AssetCatalogTreeViewUnassignedItem::DropTarget::DropTarget(AssetCatalogTreeView &tree_view)
-    : ui::AbstractViewItemDropController(tree_view)
+    : ui::AbstractViewItemDropTarget(tree_view)
 {
 }
 
-bool AssetCatalogTreeViewUnassignedItem::DropController::can_drop(
+bool AssetCatalogTreeViewUnassignedItem::DropTarget::can_drop(const wmDrag &drag,
-    const wmDrag &drag, const char **r_disabled_hint) const
+                                                              const char **r_disabled_hint) const
 {
   if (drag.type != WM_DRAG_ASSET_LIST) {
     return false;
   }
-  return AssetCatalogDropController::has_droppable_asset(drag, r_disabled_hint);
+  return AssetCatalogDropTarget::has_droppable_asset(drag, r_disabled_hint);
 }
 
-std::string AssetCatalogTreeViewUnassignedItem::DropController::drop_tooltip(
+std::string AssetCatalogTreeViewUnassignedItem::DropTarget::drop_tooltip(const wmDrag &drag) const
-    const wmDrag &drag) const
 {
   const ListBase *asset_drags = WM_drag_asset_list_get(&drag);
   const bool is_multiple_assets = !BLI_listbase_is_single(asset_drags);
@@ -666,11 +664,11 @@ std::string AssetCatalogTreeViewUnassignedItem::DropController::drop_tooltip(
                               TIP_("Move asset out of any catalog");
 }
 
-bool AssetCatalogTreeViewUnassignedItem::DropController::on_drop(struct bContext *C,
+bool AssetCatalogTreeViewUnassignedItem::DropTarget::on_drop(struct bContext *C,
-                                                                 const wmDrag &drag)
+                                                             const wmDrag &drag) const
 {
   /* Assign to nil catalog ID. */
-  return AssetCatalogDropController::drop_assets_into_catalog(
+  return AssetCatalogDropTarget::drop_assets_into_catalog(
       C, get_view<AssetCatalogTreeView>(), drag, CatalogID{});
 }