Never update ToolTipService while the mouse is over a tooltip (fixes flicker when redrawing a window beneath the pointer) (#15596)

Avoid race condition where a dispatcher timer callback exectues right after we stopped the timer
Fix not closing a tooltip when its pointer exit event is the last input sent to Avalonia

src/Avalonia.Controls/IToolTipService.cs

@@ -1,9 +1,10 @@
-using Avalonia.Metadata;
+using Avalonia.Input;
+using Avalonia.Metadata;
 
 namespace Avalonia.Controls;
 
 [Unstable, PrivateApi]
 internal interface IToolTipService
 {
-    void Update(Visual? candidateToolTipHost);
+    void Update(IInputRoot root, Visual? candidateToolTipHost);
 }

src/Avalonia.Controls/ToolTipService.cs

@@ -17,6 +17,7 @@ namespace Avalonia.Controls
         private long _lastTipCloseTime;
         private DispatcherTimer? _timer;
         private ulong _lastTipEventTime;
+        private ulong _lastWindowEventTime;
 
         public ToolTipService(IInputManager inputManager)
         {
@@ -36,18 +37,23 @@ namespace Avalonia.Controls
         {
             if (e is RawPointerEventArgs pointerEvent)
             {
+                bool isTooltipEvent = false;
                 if (_tipControl?.GetValue(ToolTip.ToolTipProperty) is { } currentTip && e.Root == currentTip.PopupHost)
+                {
+                    isTooltipEvent = true;
                     _lastTipEventTime = pointerEvent.Timestamp;
-
-                var simultaneousTipEvent = _lastTipEventTime == pointerEvent.Timestamp;
+                }
+                else if (e.Root == _tipControl?.VisualRoot)
+                {
+                    _lastWindowEventTime = pointerEvent.Timestamp;
+                }
 
                 switch (pointerEvent.Type)
                 {
-                    // sometimes there is a null hit test as soon as the pointer enters a tooltip
-                    case RawPointerEventType.Move when !(simultaneousTipEvent && pointerEvent.InputHitTestResult.element == null): 
-                        Update(pointerEvent.InputHitTestResult.element as Visual);
+                    case RawPointerEventType.Move:
+                        Update(pointerEvent.Root, pointerEvent.InputHitTestResult.element as Visual);
                         break;
-                    case RawPointerEventType.LeaveWindow when e.Root == _tipControl?.VisualRoot && !simultaneousTipEvent:
+                    case RawPointerEventType.LeaveWindow when (e.Root == _tipControl?.VisualRoot && _lastTipEventTime != e.Timestamp) || (isTooltipEvent && _lastWindowEventTime != e.Timestamp):
                         ClearTip();
                         _tipControl = null;
                         break;
@@ -68,10 +74,16 @@ namespace Avalonia.Controls
             }
         }
 
-        public void Update(Visual? candidateToolTipHost)
+        public void Update(IInputRoot root, Visual? candidateToolTipHost)
         {
             var currentToolTip = _tipControl?.GetValue(ToolTip.ToolTipProperty);
 
+            if (root == currentToolTip?.VisualRoot)
+            {
+                // Don't update while the pointer is over a tooltip
+                return;
+            }
+
             while (candidateToolTipHost != null)
             {
                 if (candidateToolTipHost == currentToolTip) // when OverlayPopupHost is in use, the tooltip is in the same window as the host control
@@ -193,7 +205,11 @@ namespace Avalonia.Controls
         private void StartShowTimer(int showDelay, Control control)
         {
             _timer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(showDelay), Tag = (this, control) };
-            _timer.Tick += (o, e) => Open(control);
+            _timer.Tick += (o, e) =>
+            {
+                if (_timer != null)
+                    Open(control);
+            };
             _timer.Start();
         }
 

src/Avalonia.Controls/TopLevel.cs

@@ -896,12 +896,12 @@ namespace Avalonia.Controls
 
         private void UpdateToolTip(Rect dirtyRect)
         {
-            if (_tooltipService != null && _pointerOverPreProcessor?.LastPosition is { } lastPos)
+            if (_tooltipService != null && IsPointerOver && _pointerOverPreProcessor?.LastPosition is { } lastPos)
             {
                 var clientPoint = this.PointToClient(lastPos);
                 if (dirtyRect.Contains(clientPoint))
                 {
-                    _tooltipService.Update(HitTester.HitTestFirst(clientPoint, this, null));
+                    _tooltipService.Update(this, HitTester.HitTestFirst(clientPoint, this, null));
                 }
             }
         }