fix bug MouseHoverLogic to make it easier to show Diff-Tooltip in editor: start MouseHover already on MouseEnter

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/MouseHoverLogic.cs

@@ -30,24 +30,34 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			this.target = target;
 			this.target.MouseLeave += MouseHoverLogicMouseLeave;
 			this.target.MouseMove += MouseHoverLogicMouseMove;
+			this.target.MouseEnter += MouseHoverLogicMouseEnter;
 		}
 		
 		void MouseHoverLogicMouseMove(object sender, MouseEventArgs e)
 		{
-			Point newPosition = e.GetPosition(this.target);
-			Vector mouseMovement = mouseHoverStartPoint - newPosition;
+			Vector mouseMovement = mouseHoverStartPoint - e.GetPosition(this.target);
 			if (Math.Abs(mouseMovement.X) > SystemParameters.MouseHoverWidth
 			    || Math.Abs(mouseMovement.Y) > SystemParameters.MouseHoverHeight)
+			{
+				StartHovering(e);
+			}
+			// do not set e.Handled - allow others to also handle MouseMove
+		}
+		
+		void MouseHoverLogicMouseEnter(object sender, MouseEventArgs e)
+		{
+			StartHovering(e);
+			// do not set e.Handled - allow others to also handle MouseEnter
+		}
+		
+		void StartHovering(MouseEventArgs e)
 		{
 			StopHovering();
-				mouseHoverStartPoint = newPosition;
+			mouseHoverStartPoint = e.GetPosition(this.target);
 			mouseHoverLastEventArgs = e;
-				mouseHoverTimer = new DispatcherTimer(SystemParameters.MouseHoverTime, DispatcherPriority.Background,
-				                                      OnMouseHoverTimerElapsed, this.target.Dispatcher);
+			mouseHoverTimer = new DispatcherTimer(SystemParameters.MouseHoverTime, DispatcherPriority.Background, OnMouseHoverTimerElapsed, this.target.Dispatcher);
 			mouseHoverTimer.Start();
 		}
-			// do not set e.Handled - allow others to also handle MouseMove
-		}
 		
 		void MouseHoverLogicMouseLeave(object sender, MouseEventArgs e)
 		{
@@ -116,6 +126,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			if (!disposed) {
 				this.target.MouseLeave -= MouseHoverLogicMouseLeave;
 				this.target.MouseMove -= MouseHoverLogicMouseMove;
+				this.target.MouseEnter -= MouseHoverLogicMouseEnter;
 			}
 			disposed = true;
 		}