WPF or silverlight XAML element collision detection.

private bool CheckCollision(FrameworkElement ctl1,FrameworkElement ctl2)
        {
            bool retval = false;
            Point ptTopLeft = new Point(Convert.ToDouble(ctl1.GetValue(Canvas.LeftProperty)), Convert.ToDouble(ctl1.GetValue(Canvas.TopProperty)));
            Point ptBottomRight = new Point(Convert.ToDouble(ctl1.GetValue(Canvas.LeftProperty)) + ctl1.Width, Convert.ToDouble(ctl1.GetValue(Canvas.TopProperty)) + ctl1.Height);
            Rect r1 = new Rect(ptTopLeft, ptBottomRight);

            //System.Diagnostics.Debug.WriteLine("+++x:" + ptTopLeft.X.ToString() + " Y " + ptTopLeft.Y.ToString() + " " + ptBottomRight.X.ToString() + " " + ptBottomRight.Y.ToString());

            Point ptTopLeft2 = new Point(Convert.ToDouble(ctl2.GetValue(Canvas.LeftProperty)), Convert.ToDouble(ctl2.GetValue(Canvas.TopProperty)));
            Point ptBottomRight2 = new Point(Convert.ToDouble(ctl2.GetValue(Canvas.LeftProperty)) + ctl2.Width, Convert.ToDouble(ctl2.GetValue(Canvas.TopProperty)) + ctl2.Height);
            Rect r2 = new Rect(ptTopLeft2, ptBottomRight2);

            r1.Intersect(r2);
            if (!r1.IsEmpty)
            {
                retval = true;
            }
            return retval;
        }