Texture Filtering Performance

Using SS:SE's Citadel demo again we'll take a look at the rendering performance of the various filter methods available on Parhelia.

Bilinear	640x480	800x600	1024x768	1280x960	1600x1200
1x	61.8	61.0	58.8	51.5	40.1
2x	60.4	59.8	56.8	47.4	34.6

 

Difference	640x480	800x600	1024x768	1280x960	1600x1200
FPS	-1.4	-1.2	-2.0	-4.1	-5.5
%	-2%	-2%	-3%	-8%	-14%

Trilinear	640x480	800x600	1024x768	1280x960	1600x1200
1x	60.9	60.0	59.4	47.9	34.8
2x	60.1	59.0	53.9	39.7	28.3

 

Difference	640x480	800x600	1024x768	1280x960	1600x1200
FPS	-0.8	-1.0	-5.5	-8.2	-6.5
%	-1%	-2%	-9%	-17%	-19%

As we would expect the performance hit for adding 2X Anisotropic filtering is larger when using Trilinear filtering than it is for Bilinear filtering. SS:SE uses lots of texture layers to begin with, so it's likely that the four bilinear sampling units per pipeline are occupied just applying the textures in the first place even with straight Bilinear filtering. Adding more complicated filtering than bilinear probably results in the texturing being applied over multiple cycles. In Trilinear two texture units will be occupied for a single texture map, so adding 2X filtering will result in all four of the texture units per pipe only sampling from a single texture layer per clock cycle.