how to do Hit testing in GDI+ ?

Question

I have a canvas that contains many shapes and every shape has a location, size and rotation angle (size and location are in inches) and I want to check if mouse position is within which shape (the rotated shape) ?? can anyone help?

Answer 1

Check this article on testing point in triangle. It is the best material I have found on this topic.

Answer 2

Your question is awfully short on details, I can only provide a generic answer. Do it mathematically is the fastest way. Rotation can make that difficult.

You can solve it slowly but easily by using a hit-test bitmap. Render the shapes to a Bitmap, using the same code you now use to render it to the screen. But now using a color that encodes the shape number. Hit testing is now simple and quick with GetPixel(). Be careful to turn off image enhancement settings, like anti-aliasing. Render it to the screen first and take a good look at the pixels with ZoomIt.

Answer 3

I found the answer (I have to convert al measurements to pixels to make sure it will calculate correctly):

public static bool HitTest(Rectangle bounds, float angle, Point location)
        {
            if (angle == 0) return bounds.Contains(location);

            using (Matrix matrix = new Matrix())
            {
                matrix.RotateAt(angle, Center(bounds));
                using (GraphicsPath path = new GraphicsPath())
                {
                    path.AddRectangle(bounds);
                    path.Transform(matrix);
                    return path.IsVisible(location.X, location.Y);
                }
            }
        }