When it comes to graphics performance in OS X, Apple has taken the conservative approach and focused on compatibility and stability in drivers instead of including the cutting-edge and highly tweaked drivers and graphics systems that bring the best quality to performance-related applications like games.
This compatibility-based approach may be good for productivity applications to prevent potential crashes, but has kept Apple behind when it comes to gaming performance. For awhile this was not an issue, but the recent release of Valve's "Steam" client for the Mac along with a few other gaming titles have not only outlined the increase in gaming on the Mac, but also the limitations faced with gaming on the Mac platform.
After Steam's release a few articles (such as this one at Anandtech) cropped up comparing the performance of Steam games on the Mac versus Windows, and it was clear OS X lagged way behind not only in performance, but also in quality. Nevertheless, the games were quite playable and Valve announced the numbers of Mac made up a significant share of the Steam user base.
With these reports and pressure from Valve and other gaming companies, Apple released the latest graphics update for OS X 10.6.4, which addressed numerous performance and feature limits in the previous drivers, and helped close the gap between OS X and Windows machines.
Valve recently commented on these improvements in a publication, and outlined what they mean for gaming performance and visual quality. The article touches on some of the technical details of the graphics systems, but is an easy read for those who enjoy these details.
Overall, among other improvements Apple has now allowed Valve to include a feature called "occlusion queries", which allows for more advanced lighting and other visual effects. Valve gives the example of a bright object causing the rest of a scene to appear hazy, as if someone is shining a flashlight in your eyes. When the light source is occluded (you cover up the flashlight), the level of haziness in the rest of the scene should go down and the scene should become crisper and detailed. With the "occlusion queries" feature, Valve can implement this in games, and have objects "occlude" each other and change visual effects like lighting in this manner, bringing out more realism in the game.
In addition to the benefits brought forth with Occlusion Queries, Valve's article does discuss some persisting drawbacks, particularly with Floating Point Validation, which is the source of another bottleneck in graphics drivers. If Apple implements some small changes to the graphics drivers to lessen the time the floating point validation is done in the drivers, apparently another big performance gain may be possible.
Despite the existing bottlenecks, in testing Mac systems are showing between 14 percent and 120 percent improvement in frame-rate performance with the latest graphics update, which is a major plus for games but also could mean improvements in other applications. Let's hope Apple continues this trend and works to improve all areas of the graphics system, for the benefit of both gamers and the rest of us.