Fix ctrl-dragging on an existing selection causing deselection of the hovered object

osu.Game/Screens/Edit/Compose/Components/BlueprintContainer.cs

@@ -135,11 +135,12 @@ namespace osu.Game.Screens.Edit.Compose.Components
 
         protected override bool OnMouseDown(MouseDownEvent e)
         {
-            if (!beginClickSelection(e)) return true;
+            bool selectionPerformed = beginClickSelection(e);
 
+            // even if a selection didn't occur, a drag event may still move the selection.
             prepareSelectionMovement();
 
-            return e.Button == MouseButton.Left;
+            return selectionPerformed || e.Button == MouseButton.Left;
         }
 
         private SelectionBlueprint clickedBlueprint;
@@ -154,7 +155,7 @@ namespace osu.Game.Screens.Edit.Compose.Components
 
             // Deselection should only occur if no selected blueprints are hovered
             // A special case for when a blueprint was selected via this click is added since OnClick() may occur outside the hitobject and should not trigger deselection
-            if (endClickSelection() || clickedBlueprint != null)
+            if (endClickSelection(e) || clickedBlueprint != null)
                 return true;
 
             deselectAll();
@@ -177,7 +178,12 @@ namespace osu.Game.Screens.Edit.Compose.Components
         protected override void OnMouseUp(MouseUpEvent e)
         {
             // Special case for when a drag happened instead of a click
-            Schedule(() => endClickSelection());
+            Schedule(() =>
+            {
+                endClickSelection(e);
+                clickSelectionBegan = false;
+                isDraggingBlueprint = false;
+            });
 
             finishSelectionMovement();
         }
@@ -226,7 +232,6 @@ namespace osu.Game.Screens.Edit.Compose.Components
                     Beatmap.Update(obj);
 
                 changeHandler?.EndChange();
-                isDraggingBlueprint = false;
             }
 
             if (DragBox.State == Visibility.Visible)
@@ -355,13 +360,28 @@ namespace osu.Game.Screens.Edit.Compose.Components
         /// <summary>
         /// Finishes the current blueprint selection.
         /// </summary>
+        /// <param name="e">The mouse event which triggered end of selection.</param>
         /// <returns>Whether a click selection was active.</returns>
-        private bool endClickSelection()
+        private bool endClickSelection(MouseButtonEvent e)
         {
-            if (!clickSelectionBegan)
+            if (!clickSelectionBegan && !isDraggingBlueprint)
-                return false;
+            {
+                // if a selection didn't occur, we may want to trigger a deselection.
+                if (e.ControlPressed && e.Button == MouseButton.Left)
+                {
+                    // Iterate from the top of the input stack (blueprints closest to the front of the screen first).
+                    // Priority is given to already-selected blueprints.
+                    foreach (SelectionBlueprint blueprint in SelectionBlueprints.AliveChildren.Reverse().OrderByDescending(b => b.IsSelected))
+                    {
+                        if (!blueprint.IsHovered) continue;
+
+                        return clickSelectionBegan = SelectionHandler.HandleDeselectionRequested(blueprint, e);
+                    }
+                }
+
+                return false;
+            }
 
-            clickSelectionBegan = false;
             return true;
         }
 

osu.Game/Screens/Edit/Compose/Components/SelectionHandler.cs

@@ -228,14 +228,33 @@ namespace osu.Game.Screens.Edit.Compose.Components
                 return false;
             }
 
-            if (e.ControlPressed && e.Button == MouseButton.Left)
+            // while holding control, we only want to add to selection, not replace an existing selection.
+            if (e.ControlPressed && e.Button == MouseButton.Left && !blueprint.IsSelected)
+            {
                 blueprint.ToggleSelection();
-            else
-                ensureSelected(blueprint);
-
                 return true;
             }
 
+            return ensureSelected(blueprint);
+        }
+
+        /// <summary>
+        /// Handle a blueprint requesting selection.
+        /// </summary>
+        /// <param name="blueprint">The blueprint.</param>
+        /// <param name="e">The mouse event responsible for deselection.</param>
+        /// <returns>Whether a deselection was performed.</returns>
+        internal bool HandleDeselectionRequested(SelectionBlueprint blueprint, MouseButtonEvent e)
+        {
+            if (blueprint.IsSelected)
+            {
+                blueprint.ToggleSelection();
+                return true;
+            }
+
+            return false;
+        }
+
         private void handleQuickDeletion(SelectionBlueprint blueprint)
         {
             if (blueprint.HandleQuickDeletion())
@@ -247,13 +266,19 @@ namespace osu.Game.Screens.Edit.Compose.Components
                 deleteSelected();
         }
 
-        private void ensureSelected(SelectionBlueprint blueprint)
+        /// <summary>
+        /// Ensure the blueprint is in a selected state.
+        /// </summary>
+        /// <param name="blueprint">The blueprint to select.</param>
+        /// <returns>Whether selection state was changed.</returns>
+        private bool ensureSelected(SelectionBlueprint blueprint)
         {
             if (blueprint.IsSelected)
-                return;
+                return false;
 
             DeselectAll?.Invoke();
             blueprint.Select();
+            return true;
         }
 
         private void deleteSelected()