AvalonEdit: don't unnecessarily update the mouse cursor.

Author: dgrunwald

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/TextArea.cs

@@ -966,14 +966,14 @@ protected override void OnPreviewKeyUp(KeyEventArgs e)
 		protected override void OnKeyDown(KeyEventArgs e)
 		{
 			base.OnKeyDown(e);
-			TextView.InvalidateCursor();
+			TextView.InvalidateCursorIfMouseWithinTextView();
 		}
 
 		/// <inheritdoc/>
 		protected override void OnKeyUp(KeyEventArgs e)
 		{
 			base.OnKeyUp(e);
-			TextView.InvalidateCursor();
+			TextView.InvalidateCursorIfMouseWithinTextView();
 		}
 		#endregion
 

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

@@ -1165,7 +1165,7 @@ protected override Size ArrangeOverride(Size finalSize)
 					}
 				}
 			}
-			InvalidateCursor();
+			InvalidateCursorIfMouseWithinTextView();
 
 			return finalSize;
 		}
@@ -1636,6 +1636,15 @@ public static void InvalidateCursor()
 			}
 		}
 
+		internal void InvalidateCursorIfMouseWithinTextView()
+		{
+			// Don't unnecessarily call Mouse.UpdateCursor() if the mouse is outside the text view.
+			// Unnecessary updates may cause the mouse pointer to flicker
+			// (e.g. if it is over a window border, it blinks between Resize and Normal)
+			if (this.IsMouseOver)
+				InvalidateCursor();
+		}
+		
 		/// <inheritdoc/>
 		protected override void OnQueryCursor(QueryCursorEventArgs e)
 		{