How commercial game accomplsih stunnning graphics with smooth game play? I am a huge die hard fan and follower of GNU Stallman and his philosophies and other Libre people Cmon how wud I miss Linus. but I got to admit commercial games does excellent jobs. One such good example is Assasin's Creed from Ubisoft.

It has good quality graphcis and plays smoothly in my Dual core CPU with Nvidia Geforce 8400ES. Rockstar GTA4 has awesome graphcis but it's slower than AC considering the graphics quality tradeoff. Age of Empires from Ensemble studios, does include Massive crowd AI simulation, yet it plays so smoothly with eyecandy graphics and very large weapon sets and different techtree elements

on the other hand. Open source games like Glest, 0A.D(still in alpha :) are not so smooth even though they have very restricted abilities?

Coming to question: how do game companies achieve such optmizations, or the open source community is not doing optimizations, or there are any propriarity technological elements that benefits only the companies exists huh?? e.g the OpenSubDiv from Pixar just released open to community?? something like that. and why it is hard to implement optimizations? are there any legal restrictions???