Get coordinates after rotation

Question

I have a usercontrol which contains a rectangle and 2 ellipses on the left and right edge of the rectangle. I am intrested in finding out the coordinates of the user control after a translate and rotation rendertransform has occured.

The user control is contained in a canvas.

EDIT: After searching the internet for a while i was able to find the answer to my question here http://forums.silverlight.net/forums/p/136759/305241.aspx so I thought i'd post the link for other people having this issue.

I've marked Tomas Petricek's post as an answer because it was the closest one to the solution.

Answer 1

If you want to implement the calculation yourself, then you can use the following method to calculate a location of a point after rotation (by a specified number of degrees):

public Point RotatePoint(float angle, Point pt) { 
   var a = angle * System.Math.PI / 180.0;
   float cosa = Math.Cos(a), sina = Math.Sin(a);
   return new Point(pt.X * cosa - pt.Y * sina, pt.X * sina + pt.Y * cosa);
}

In general, you can represent transformations as matrices. To compose transformations, you'd just multiply the matrices, so this is a very composable solution. The matrix to represent rotation contains the sin and cos values from the method above. See Rotation matrix (and Transformation matrix) on Wikipedia.