OpenCSG is a library that does image-based Constructive Solid Geometry
rendering using OpenGL.

To run OpenCSG well, you should have graphics hardware with a good fill
rate.  NVidia GeForce and ATI Radeon qualify.  The OpenCSG::OcclusionQuery
option requires occlusion queries, which are available since Radeon 9x00
(x>=5) and GeForce3 (but not GeForce4MX).
