I've implemented a clipping and capping view similar to the example called "simplecap.zip" in this page:
This uses the stencil buffer to find the pixels drawn from inside the shape and fill them with a plane.
I'm not looking for a way to outline the clipping cap with a constant width line.
Obviously I can't just draw it since the clipping polygon is not actual geometry that I have. I've tried coming up with some more stencil buffer magic but couldn't figure out how to do it