HijackGL is a system in development by Alex Mohr and Christopher Herrman under the direction of Michael Gleicher at the University of Wisconsin. The goal of this work is to develop a system that allows us to explore what can be done by intercepting, interpreting, and transforming the calls an application makes to the OpenGL graphics library. Preliminary work on this system led to research presented at the 2001 Interactive 3D Graphics Symposium. This work focused on generating non-photorealistic renderers for existing applications. For example, we demonstrated a pencil-sketch-style renderer running on id Software's Quake III Arena, as shown at the top of this page. We did not modify the source code of Quake III Arena at all. In fact, we do not even have access to the Quake III Arena source code. Current work involves developing a more general system to allow us to experiment with other kinds of non-invasive extensions.

See their project page