1 files changed, 73 insertions, 22 deletions

diff --git a/source/blender/editors/interface/tree_view.cc b/source/blender/editors/interface/tree_view.cc
index 88aa362deb5..c08fa51d5a5 100644
--- a/source/blender/editors/interface/tree_view.cc
+++ b/source/blender/editors/interface/tree_view.cc
@@ -29,6 +29,7 @@
 
 #include "UI_interface.h"
 
+#include "WM_api.h"
 #include "WM_types.h"
 
 #include "UI_tree_view.hh"
@@ -354,22 +355,18 @@ void AbstractTreeViewItem::is_active(IsActiveFn is_active_fn)
   is_active_fn_ = is_active_fn;
 }
 
-bool AbstractTreeViewItem::on_drop(const wmDrag & /*drag*/)
+std::unique_ptr<AbstractTreeViewItemDragController> AbstractTreeViewItem::create_drag_controller()
+    const
 {
-  /* Do nothing by default. */
-  return false;
-}
-
-bool AbstractTreeViewItem::can_drop(const wmDrag & /*drag*/) const
-{
-  return false;
+  /* There's no drag controller (and hence no drag support) by default. */
+  return nullptr;
 }
 
-std::string AbstractTreeViewItem::drop_tooltip(const bContext & /*C*/,
-                                               const wmDrag & /*drag*/,
-                                               const wmEvent & /*event*/) const
+std::unique_ptr<AbstractTreeViewItemDropController> AbstractTreeViewItem::create_drop_controller()
+    const
 {
-  return TIP_("Drop into/onto tree item");
+  /* There's no drop controller (and hence no drop support) by default. */
+  return nullptr;
 }
 
 bool AbstractTreeViewItem::can_rename() const
@@ -553,6 +550,12 @@ void AbstractTreeViewItem::change_state_delayed()
     activate();
   }
 }
+/* ---------------------------------------------------------------------- */
+
+AbstractTreeViewItemDropController::AbstractTreeViewItemDropController(AbstractTreeView &tree_view)
+    : tree_view_(tree_view)
+{
+}
 
 /* ---------------------------------------------------------------------- */
 
@@ -646,7 +649,18 @@ BasicTreeViewItem::BasicTreeViewItem(StringRef label, BIFIconID icon_) : icon(ic
 
 void BasicTreeViewItem::build_row(uiLayout &row)
 {
-  uiItemL(&row, label_.c_str(), icon);
+  add_label(row);
+}
+
+void BasicTreeViewItem::add_label(uiLayout &layout, StringRefNull label_override)
+{
+  const StringRefNull label = label_override.is_empty() ? StringRefNull(label_) : label_override;
+
+  /* Some padding for labels without collapse chevron and no icon. Looks weird without. */
+  if (icon == ICON_NONE && !is_collapsible()) {
+    uiItemS_ex(&layout, 0.8f);
+  }
+  uiItemL(&layout, label.c_str(), icon);
 }
 
 void BasicTreeViewItem::on_activate()
@@ -680,19 +694,53 @@ bool UI_tree_view_item_matches(const uiTreeViewItemHandle *a_handle,
   return a.matches_including_parents(b);
 }
 
-bool UI_tree_view_item_can_drop(const uiTreeViewItemHandle *item_, const wmDrag *drag)
+/**
+ * Attempt to start dragging the tree-item \a item_. This will not work if the tree item doesn't
+ * support dragging, i.e. it won't create a drag-controller upon request.
+ * \return True if dragging started successfully, otherwise false.
+ */
+bool UI_tree_view_item_drag_start(bContext *C, uiTreeViewItemHandle *item_)
+{
+  const AbstractTreeViewItem &item = reinterpret_cast<const AbstractTreeViewItem &>(*item_);
+  const std::unique_ptr<AbstractTreeViewItemDragController> drag_controller =
+      item.create_drag_controller();
+  if (!drag_controller) {
+    return false;
+  }
+
+  WM_event_start_drag(C,
+                      ICON_NONE,
+                      drag_controller->get_drag_type(),
+                      drag_controller->create_drag_data(),
+                      0,
+                      WM_DRAG_FREE_DATA);
+  return true;
+}
+
+bool UI_tree_view_item_can_drop(const uiTreeViewItemHandle *item_,
+                                const wmDrag *drag,
+                                const char **r_disabled_hint)
 {
   const AbstractTreeViewItem &item = reinterpret_cast<const AbstractTreeViewItem &>(*item_);
-  return item.can_drop(*drag);
+  const std::unique_ptr<AbstractTreeViewItemDropController> drop_controller =
+      item.create_drop_controller();
+  if (!drop_controller) {
+    return false;
+  }
+
+  return drop_controller->can_drop(*drag, r_disabled_hint);
 }
 
-char *UI_tree_view_item_drop_tooltip(const uiTreeViewItemHandle *item_,
-                                     const bContext *C,
-                                     const wmDrag *drag,
-                                     const wmEvent *event)
+char *UI_tree_view_item_drop_tooltip(const uiTreeViewItemHandle *item_, const wmDrag *drag)
 {
   const AbstractTreeViewItem &item = reinterpret_cast<const AbstractTreeViewItem &>(*item_);
-  return BLI_strdup(item.drop_tooltip(*C, *drag, *event).c_str());
+  const std::unique_ptr<AbstractTreeViewItemDropController> drop_controller =
+      item.create_drop_controller();
+  if (!drop_controller) {
+    return nullptr;
+  }
+
+  return BLI_strdup(drop_controller->drop_tooltip(*drag).c_str());
 }
 
 /**
@@ -702,10 +750,13 @@ char *UI_tree_view_item_drop_tooltip(const uiTreeViewItemHandle *item_,
 bool UI_tree_view_item_drop_handle(uiTreeViewItemHandle *item_, const ListBase *drags)
 {
   AbstractTreeViewItem &item = reinterpret_cast<AbstractTreeViewItem &>(*item_);
+  std::unique_ptr<AbstractTreeViewItemDropController> drop_controller =
+      item.create_drop_controller();
 
+  const char *disabled_hint_dummy = nullptr;
   LISTBASE_FOREACH (const wmDrag *, drag, drags) {
-    if (item.can_drop(*drag)) {
-      return item.on_drop(*drag);
+    if (drop_controller->can_drop(*drag, &disabled_hint_dummy)) {
+      return drop_controller->on_drop(*drag);
     }
   }