Gl ztrick

Name: gl_ztrick
Default value: "1"
Cvar flags: None
FTEQW Builds: OpenGL Renderer Minimal GL Build Merged Build Linux Build

~copied from FuhQuake manual~
gl_ztrick (0/1) {GL only}
This variables toggles the use of a trick to prevent the clearning of the
z-buffer between frames. When this variable is set to "1", the game will not
clear the z-buffer between frames. This will result in increased performance
but might cause problems for some display hardware.
0 = Do not use the z-buffer trick.
1 = Use the z-buffer trick.

IRC QUOTE:
�LordHavoc� Moodles: GF3 and Radeon and later cards have zbuffer optimizations that only work if ztrick is off
�LordHavoc� Moodles: mainly Radeon I believe

QuakeSRC Wiki Quote:

gl_ztrick enables/disables the use of a trick that allows the renderer to avoid clearing the depth buffer every frame. This results in a slight speed increase, with a trade off for less depth precision.

(The performance gained from turning this on is barely noticeable on newer accelerator cards, so it would be better to turn it off if you have a TNT2 or better)