Windows Vista May Degrade OpenGL
Microsoft's current plan for OpenGL on Windows Vista is to layer OpenGL over Direct3D in order to use OpenGL with a composited desktop to obtain the Aeroglass experience. This means that OpenGL performance will be significantly reduced - perhaps as much as 50%. It would be technically straightforward to provide an OpenGL ICD within the full Aeroglass experience without compromising the stability or the security of the operating system. Layering OpenGL over Direct3D is a policy more than a technical decision.