Fast Z Reject: ATI Performance Booster?
Even though ATI RADEON 9800- and X800-hardware performs quite well in Half-Life 2, there may be an additional way to improve the speed of the RADEON graphics processing units. Due to some reason, Valve disabled the so-called Fast Z Reject capability of the RADEON hardware.
According to information from Beyond3D, activation of Fast Z Reject enables Z fill geometry pass in order to speed up rendering of the full scene rendering pass.
Fortunately, FastZReject can be enabled by a console command 'fastzreject 1'. We tried to activate the feature that is present by default on the GeForce FX and GeForce 6 hardware, but is unavailable, at least for now, on ATI's VPUs. We used two of our demos along with the CATALYST 4.12 beta driver to test whether the Fast Z Reject brings any advantages to the RADEON X800 XT Platinum Edition and RADEON X800 PRO.
Well, at least in our conditions the Fast Z Reject brought no performance gains at all; maybe this should be attributed to our demos, maybe CATALYST4.12 beta driver turns this on by default, maybe Valve has quietly enabled Fast Z Reject for the RADEON X800 in a minor update for the game (since we run the game via the Steam software, we receive updates automatically).