Question

I am responding to MouseLeftButtonDown events on elements added to a WPF canvas. It all works fine when clicked (i.e. the eventhandler fires off correctly), but it requires too much precision from the mouse pointer. You have to be perfectly on top of the circle to make it work. I need it to be a little more forgiving; maybe at least 1 or 2 pixles forgiving. The elements on the canvas are nice big circles (about the size of a quarter on the screen), so the circles themselves are not too small, but the StrokeWidth of each one is 1, so it is a thin line.

You can see a screenshot here: http://twitpic.com/1f2ci/full

Most graphics app aren’t this picky about the mouse picking, so I want to give the user a familiar experience.

How can I make it a little more forgiving.

Answer 1

You can hook up to the MouseLeftButtonDown event of your root layout object instead, and check which elements is in range of a click by doing this:

List<UIElement> hits = System.Windows.Media.VisualTreeHelper.FindElementsInHostCoordinates(Point, yourLayoutRootElement) as List<UIElement>;   

http://msdn.microsoft.com/en-us/library/cc838402(VS.95).aspx

For the Point parameter, you can use the MouseEventArgs parameter e, and call its GetPosition method like this:

Point p = e.GetPosition(null) 

I can’t remember whether to use HitTest instead of the FindElementsInHostCoordinates. Try both.
http://msdn.microsoft.com/en-us/library/ms608752.aspx

You could create 4 Point objects from the mouse position to create a fake tolerence effect, and call either FindElementsInHostCoordinates or HitTest for all 4 points.