Z Rejection Performance

Dependant on the organisation of the pipelines the Z rejection rate may scale with the shader pipelines. We'll take a look using the GL_REME application that test various render orders, looking at them in relation to the back to front order, which is the worst case scenario for early pixel rejection.

GL_Reme (FPS) Back to Front Front to Back Random % Improvement from Back to Front
Front to Back Random
7800 GTX Overdraw Factor 3 1507.4 3110.5 2113.5 106% 40%
Overdraw Facter 8 594.2 2166.5 1316.4 265% 122%
6800 Ultra Overdraw Factor 3 1017.6 2297.5 1482.7 126% 46%
Overdraw Facter 8 395.7 1735.3 949.3 339% 140%

Here we see that although the 7800 GTX has a higher performance in each of the modes, the 7800 GTX isn't quite as efficient as the 6800 Ultra. The difference is not significant enough to suggest that there is much in the way of differences between the two but perhaps there is a little loss of efficiency due to the wider pipeline of the 7800.


Stencil Performance

Game Test 2 in Futuremark's benchmark application 3DMark03 uses an early Z pass and stencil buffered shadows, so we'll look at the rendering performance of the 7800 GTX in this to see how it fares in relation to the 6800 Ultra in a stencil heavy scene.

3DMark03 - GT2 640x480 800x600 1024x768 1280x1024 1600x1200
7800 GTX 194.5 163.9 130.6 97.4 75.1
6800 Ultra 155.6 130.4 103.6 77.4 60.3

640x480 800x600 1024x768 1280x1024 1600x1200
7800 GTX % Faster than 6800 Ultra 25.0% 25.7% 26.1% 25.8% 24.5%

As we've seen before, the double Z rate of previous NVIDIA parts carries across to G70 hence the 7800 GTX still has a performance advantage over the 6800 Ultra in this test. The difference is, in fact, larger than the pure stencil performance difference would suggest, which is likely due to the increased shader capabilities.