Allow invalidating mouse position state

osu.Framework/Input/InputManager.cs

@@ -128,7 +128,7 @@ public Drawable DraggedDrawable
         /// <remarks>
         /// This collection should not be retained as a reference. The contents is not stable outside of local usage.
         /// </remarks>
-        public SlimReadOnlyListWrapper<Drawable> PositionalInputQueue => buildPositionalInputQueue(CurrentState.Mouse.Position);
+        public SlimReadOnlyListWrapper<Drawable> PositionalInputQueue => buildPositionalInputQueue(!CurrentState.Mouse.IsPositionValid ? null : CurrentState.Mouse.Position);
 
         /// <summary>
         /// Contains all <see cref="Drawable"/>s in top-down order which are considered
@@ -627,10 +627,13 @@ private SlimReadOnlyListWrapper<Drawable> buildNonPositionalInputQueue()
 
         private readonly List<Drawable> positionalInputQueue = new List<Drawable>();
 
-        private SlimReadOnlyListWrapper<Drawable> buildPositionalInputQueue(Vector2 screenSpacePos)
+        private SlimReadOnlyListWrapper<Drawable> buildPositionalInputQueue(Vector2? screenSpacePos)
         {
             positionalInputQueue.Clear();
 
+            if (screenSpacePos == null)
+                return positionalInputQueue.AsSlimReadOnly();
+
             if (this is UserInputManager)
                 FrameStatistics.Increment(StatisticsCounterType.PositionalIQ);
 
@@ -639,7 +642,7 @@ private SlimReadOnlyListWrapper<Drawable> buildPositionalInputQueue(Vector2 scre
             for (int i = 0; i < children.Count; i++)
             {
                 if (ShouldBeConsideredForInput(children[i]))
-                    children[i].BuildPositionalInputQueue(screenSpacePos, positionalInputQueue);
+                    children[i].BuildPositionalInputQueue(screenSpacePos.Value, positionalInputQueue);
             }
 
             positionalInputQueue.Reverse();
@@ -959,16 +962,19 @@ protected virtual void HandleMousePositionChange(MousePositionChangeEvent e)
             var state = e.State;
             var mouse = state.Mouse;
 
-            foreach (var h in InputHandlers)
+            if (e.LastPosition != null)
             {
-                if (h.Enabled.Value && h is INeedsMousePositionFeedback handler)
-                    handler.FeedbackMousePositionChange(mouse.Position, h == mouseSource);
-            }
+                foreach (var h in InputHandlers)
+                {
+                    if (h.Enabled.Value && h is INeedsMousePositionFeedback handler)
+                        handler.FeedbackMousePositionChange(mouse.Position, h == mouseSource);
+                }
 
-            handleMouseMove(state, e.LastPosition);
+                handleMouseMove(state, e.LastPosition.Value);
 
-            foreach (var manager in mouseButtonEventManagers.Values)
-                manager.HandlePositionChange(state, e.LastPosition);
+                foreach (var manager in mouseButtonEventManagers.Values)
+                    manager.HandlePositionChange(state, e.LastPosition.Value);
+            }
 
             updateHoverEvents(state);
         }

osu.Framework/Input/StateChanges/Events/MousePositionChangeEvent.cs

@@ -9,9 +9,9 @@ namespace osu.Framework.Input.StateChanges.Events
     public class MousePositionChangeEvent : InputStateChangeEvent
     {
         /// <summary>
-        /// The last mouse position.
+        /// The last mouse position, or null if the event is invalidation of the mouse position state.
         /// </summary>
-        public readonly Vector2 LastPosition;
+        public readonly Vector2? LastPosition;
 
         public MousePositionChangeEvent(InputState state, IInput input, Vector2 lastPosition)
             : base(state, input)

osu.Framework/Input/StateChanges/MouseInvalidatePositionInput.cs

@@ -0,0 +1,28 @@
+// Copyright (c) ppy Pty Ltd <[email protected]>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Input.StateChanges.Events;
+using osu.Framework.Input.States;
+
+namespace osu.Framework.Input.StateChanges
+{
+    /// <summary>
+    /// Denotes an invalidation of the current mouse position,
+    /// mainly used when a single remaining touch source is released,
+    /// or a hovering pen (e.g. Apple Pencil) leaves the screen area.
+    /// </summary>
+    public class MouseInvalidatePositionInput : IInput
+    {
+        public void Apply(InputState state, IInputStateChangeHandler handler)
+        {
+            var mouse = state.Mouse;
+
+            if (mouse.IsPositionValid)
+            {
+                mouse.IsPositionValid = false;
+                mouse.LastSource = this;
+                handler.HandleInputStateChange(new MousePositionChangeEvent(state, this, mouse.Position));
+            }
+        }
+    }
+}

osu.Framework/Input/StateChanges/MouseInvalidatePositionInputFromTouch.cs

@@ -0,0 +1,17 @@
+// Copyright (c) ppy Pty Ltd <[email protected]>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Input.StateChanges.Events;
+
+namespace osu.Framework.Input.StateChanges
+{
+    public class MouseInvalidatePositionInputFromTouch : MouseInvalidatePositionInput, ISourcedFromTouch
+    {
+        public MouseInvalidatePositionInputFromTouch(TouchStateChangeEvent touchEvent)
+        {
+            TouchEvent = touchEvent;
+        }
+
+        public TouchStateChangeEvent TouchEvent { get; }
+    }
+}