Does parallels use primary graphics card, and does it take advantage of nvidia Optimu

Im planing on buying a Mac, but I want windows so that I can play all my games and run other windows apps. The only thing is that I'm wondering after I've heard that if I run windows 7 in parallels, it would either only use the integritet graphics card(intel HD graphics 4000, since os x is using the i nvidia graphics card) or it will still use invidia Optimus, but don't take advantage of nvidia Optimus, which is essential for gaming(don't critizise me for planing to game on a Mac, because I'm not playing BF3 or crisis2)