Tree View: Multi-select support

Add support to select multiple tree view elements (similar to outliner/anim channels)
`Ctrl + LMB` to select+activate element under the mouse
`Shift + LMB` to select all items between active and clicked item.

As of now, only Shape key has support for multi-select. (straightforward to include
other views). `KEYBLOCK_SEL` flag is used for storing selection state.

Pull Request: https://projects.blender.org/blender/blender/pulls/138979

scripts/presets/keyconfig/keymap_data/blender_default.py

@@ -1043,6 +1043,10 @@ def km_user_interface(_params):
         ("ui.view_scroll", {"type": 'WHEELDOWNMOUSE', "value": 'ANY'}, None),
         ("ui.view_scroll", {"type": 'TRACKPADPAN', "value": 'ANY'}, None),
         ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'PRESS'}, None),
+        ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'PRESS', "ctrl": True},
+         {"properties": [("extend", True)]}),
+        ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'PRESS', "shift": True},
+         {"properties": [("range_select", True)]}),
     ])
 
     return keymap

source/blender/editors/include/UI_abstract_view.hh

@@ -76,6 +76,7 @@ class AbstractView {
   std::string context_menu_title;
   /** See #set_popup_keep_open(). */
   bool popup_keep_open_ = false;
+  bool is_multiselect_supported_ = false;
 
  public:
   virtual ~AbstractView() = default;
@@ -152,6 +153,8 @@ class AbstractView {
   void set_popup_keep_open();
 
   void clear_search_highlight();
+  void allow_multiselect_items();
+  bool is_multiselect_supported() const;
 
  protected:
   AbstractView() = default;
@@ -199,6 +202,7 @@ class AbstractViewItem {
   bool is_activatable_ = true;
   bool is_interactive_ = true;
   bool is_active_ = false;
+  bool is_selected_ = false;
   bool is_renaming_ = false;
   /** See #is_search_highlight(). */
   bool is_highlighted_search_ = false;
@@ -232,6 +236,8 @@ class AbstractViewItem {
    */
   virtual std::optional<bool> should_be_active() const;
 
+  virtual std::optional<bool> should_be_selected() const;
+  virtual void set_selected(const bool select);
   /**
    * Queries if the view item supports renaming in principle. Renaming may still fail, e.g. if
    * another item is already being renamed.
@@ -306,6 +312,7 @@ class AbstractViewItem {
    * can't be sure about the item state.
    */
   bool is_active() const;
+  bool is_selected() const;
   /**
    * Should this item be highlighted as matching search result? Only one item should be highlighted
    * this way at a time. Pressing enter will activate it.

source/blender/editors/interface/interface_ops.cc

@@ -2792,16 +2792,47 @@ static void UI_OT_view_item_rename(wmOperatorType *ot)
   ot->flag = OPTYPE_INTERNAL;
 }
 
-static wmOperatorStatus ui_view_item_select_exec(bContext *C, wmOperator * /*op*/)
+static wmOperatorStatus ui_view_item_select_invoke(bContext *C,
+                                                   wmOperator *op,
+                                                   const wmEvent * /*event*/)
 {
   const wmWindow &win = *CTX_wm_window(C);
   const ARegion &region = *CTX_wm_region(C);
 
-  if (AbstractViewItem *active_item = UI_region_views_find_item_at(region, win.eventstate->xy)) {
-    active_item->activate(*C);
+  AbstractViewItem *clicked_item = UI_region_views_find_item_at(region, win.eventstate->xy);
+  if (clicked_item == nullptr) {
+    return OPERATOR_CANCELLED;
+  }
+
+  AbstractView &view = clicked_item->get_view();
+  const bool is_multiselect = view.is_multiselect_supported();
+  const bool extend = RNA_boolean_get(op->ptr, "extend") && is_multiselect;
+  const bool range_select = RNA_boolean_get(op->ptr, "range_select") && is_multiselect;
+
+  if (!extend) {
+    /* Keep previous selection for extend selection, see: !138979. */
+    view.foreach_view_item([](AbstractViewItem &item) { item.set_selected(false); });
+  }
+
+  if (range_select) {
+    bool is_inside_range = false;
+    view.foreach_view_item([&](AbstractViewItem &item) {
+      if ((item.is_active()) ^ (&item == clicked_item)) {
+        is_inside_range = !is_inside_range;
+        /* Select end items from the range. */
+        item.set_selected(true);
+      }
+      if (is_inside_range) {
+        /* Select items within the range. */
+        item.set_selected(true);
+      }
+    });
     return OPERATOR_FINISHED;
   }
-  return OPERATOR_CANCELLED;
+
+  clicked_item->activate(*C);
+
+  return OPERATOR_FINISHED;
 }
 
 static void UI_OT_view_item_select(wmOperatorType *ot)
@@ -2810,10 +2841,19 @@ static void UI_OT_view_item_select(wmOperatorType *ot)
   ot->idname = "UI_OT_view_item_select";
   ot->description = "Activate selected view item";
 
-  ot->exec = ui_view_item_select_exec;
+  ot->invoke = ui_view_item_select_invoke;
   ot->poll = ui_view_focused_poll;
 
   ot->flag = OPTYPE_INTERNAL;
+
+  PropertyRNA *prop = RNA_def_boolean(ot->srna, "extend", false, "extend", "Extend Selection");
+  RNA_def_property_flag(prop, PROP_SKIP_SAVE);
+  prop = RNA_def_boolean(ot->srna,
+                         "range_select",
+                         false,
+                         "Range Select",
+                         "Select all between clicked and active items");
+  RNA_def_property_flag(prop, PROP_SKIP_SAVE);
 }
 /** \} */
 

source/blender/editors/interface/interface_widgets.cc

@@ -44,6 +44,8 @@
 #include "GPU_matrix.hh"
 #include "GPU_state.hh"
 
+#include "UI_abstract_view.hh"
+
 #ifdef WITH_INPUT_IME
 #  include "WM_types.hh"
 #endif
@@ -4369,9 +4371,17 @@ static void widget_list_itembut(uiBut *but,
                                 const float zoom)
 {
   rcti draw_rect = *rect;
+  bool is_selected = state->but_flag & UI_SELECT;
 
   if (but->type == UI_BTYPE_VIEW_ITEM) {
     uiButViewItem *item_but = static_cast<uiButViewItem *>(but);
+    blender::ui::AbstractViewItem &view_item = *item_but->view_item;
+
+    if (!view_item.is_active() && view_item.is_selected()) {
+      copy_v4_v4_uchar(wcol->inner, wcol->inner_sel);
+      color_blend_v3_v3(wcol->inner, wcol->outline, 0.5);
+      is_selected = true;
+    }
     if (item_but->draw_width > 0) {
       BLI_rcti_resize_x(&draw_rect, zoom * item_but->draw_width);
     }
@@ -4388,7 +4398,7 @@ static void widget_list_itembut(uiBut *but,
 
   if (state->but_flag & UI_HOVER) {
     color_blend_v3_v3(wcol->inner, wcol->text, 0.2);
-    wcol->inner[3] = (state->but_flag & UI_SELECT) ? 255 : 20;
+    wcol->inner[3] = is_selected ? 255 : 20;
   }
 
   widgetbase_draw(&wtb, wcol);

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

@@ -246,6 +246,16 @@ void AbstractView::clear_search_highlight()
 {
   this->foreach_view_item([](AbstractViewItem &item) { item.is_highlighted_search_ = false; });
 }
+
+void AbstractView::allow_multiselect_items()
+{
+  is_multiselect_supported_ = true;
+}
+
+bool AbstractView::is_multiselect_supported() const
+{
+  return is_multiselect_supported_;
+}
 /** \} */
 
 }  // namespace blender::ui

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

@@ -30,6 +30,7 @@ void AbstractViewItem::update_from_old(const AbstractViewItem &old)
   is_active_ = old.is_active_;
   is_renaming_ = old.is_renaming_;
   is_highlighted_search_ = old.is_highlighted_search_;
+  is_selected_ = old.is_selected_;
 }
 
 /** \} */
@@ -71,6 +72,7 @@ void AbstractViewItem::activate(bContext &C)
 {
   if (set_state_active()) {
     on_activate(C);
+    set_selected(true);
   }
 }
 
@@ -79,6 +81,16 @@ void AbstractViewItem::deactivate()
   is_active_ = false;
 }
 
+std::optional<bool> AbstractViewItem::should_be_selected() const
+{
+  return std::nullopt;
+}
+
+void AbstractViewItem::set_selected(const bool select)
+{
+  is_selected_ = select;
+}
+
 /** \} */
 
 /* ---------------------------------------------------------------------- */
@@ -97,6 +109,9 @@ void AbstractViewItem::change_state_delayed()
       is_active_ = false;
     }
   }
+  if (std::optional<bool> is_selected = should_be_selected()) {
+    set_selected(is_selected.value_or(false));
+  }
 }
 
 /** \} */
@@ -320,6 +335,13 @@ bool AbstractViewItem::is_active() const
   return is_active_;
 }
 
+bool AbstractViewItem::is_selected() const
+{
+  BLI_assert_msg(this->get_view().is_reconstructed(),
+                 "State can't be queried until reconstruction is completed");
+  return is_selected_;
+}
+
 bool AbstractViewItem::is_search_highlight() const
 {
   return is_highlighted_search_;

source/blender/editors/object/interface_template_shape_key_tree.cc

@@ -197,6 +197,17 @@ class ShapeKeyItem : public ui::AbstractTreeViewItem {
     ED_undo_push(&C, "Set Active Shape Key");
   }
 
+  std::optional<bool> should_be_selected() const override
+  {
+    return shape_key_.kb->flag & KEYBLOCK_SEL;
+  }
+
+  void set_selected(const bool select) override
+  {
+    AbstractViewItem::set_selected(select);
+    SET_FLAG_FROM_TEST(shape_key_.kb->flag, select, KEYBLOCK_SEL);
+  }
+
   bool supports_renaming() const override
   {
     return true;
@@ -256,6 +267,7 @@ void template_tree(uiLayout *layout, bContext *C)
       std::make_unique<ed::object::shapekey::ShapeKeyTreeView>(*ob));
   tree_view->set_context_menu_title("Shape Key");
   tree_view->set_default_rows(4);
+  tree_view->allow_multiselect_items();
 
   ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *layout);
 }