Quick answer is: set
Region for your form or any other control you want to make non-rectangular:
http://msdn.microsoft.com/en-us/library/windows/desktop/dd145102%28v=vs.85%29.aspx[
^],
http://msdn.microsoft.com/en-us/library/system.windows.forms.control.region(v=vs.110).aspx[
^].
The exact way depends on what you are using, so next time please provide relevant information on your problem. I referenced two MSDN articles which are most likely you would be using, but in practice you will need just one.
Now, the problem is that you will cut out all or part of the
non-client area of your window, such as title bar, close/minimize buttons, icon, etc. One of the approaches would be mimicking the non-client areas you need in the client area. In particular, you may need to implement window move, moving it by dragging by the mouse.
—SA