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D3D Texture sizes...

Started by simon_brown75 Jun 26, 2000 at 6:26 AM 5 replies 300+ views

Original Post

Jun 26, 2000 at 6:26 AM

I have a question about texture sizes in D3D. I''ve written a D3D program with 256*256 textures, and my Voodoo 3 supports this size, but if I shrink the textures to 64*64 I get a 38% speed increase! Now that''s a big difference in performace. I''ve also been looking at a few games, like Quake 2, which also seems to use 64*64 textures. Is there some good reason why using 256*256 textures should be a lot slower or is it just a failing of the V3 or it''s drivers? Thanks, Simon.

WitchLord

Jun 26, 2000 at 6:49 AM

It''s faster with smaller textures because there is less data that needs to be transported from system memory to video memory. If all textures fit in video memory then there should be no speed difference.

- WitchLord

simon_brown75

Jun 26, 2000 at 7:03 AM

Thanks for replying. I've just checked and the textures are definitely in video memory. I'm only using about 250k of vram for the textures so there shouldn't be any problems really.

Actually, i've just been doing some testing and the problem can be even worse than I described. Running in 640*480 without v-sync with 64*64 textures my program runs 253 fps, but the same exe just with 256*256 textures slow down to 140 fps. Has anyone else experienced this, or am I just doing something wrong?
Thanks,
Simon.

Edited by - simon_brown75 on June 26, 2000 8:31:52 AM

mhkrause

Jun 26, 2000 at 9:37 PM

I would wager that the performance increase is due to better utilization of the texel cache in the rasterizer.

The rasterizer on the card maintains a cache of recently hit texels. If the texture is smaller, the odds that the texels needed are in the cache increases.

This is why using mipmaps and texture compression can increase performance.

simon_brown75

Jun 27, 2000 at 8:21 AM

I''m sure that''s true to some extents, but the performance difference I''m getting is huge. From 253fps down to 140fps! Surely there are D3D games out there that use textures bigger than 64*64. Unreal Tournament is fast on my V3 in D3D mode, and surely that uses textures bigger than 64*64?

Mr Cucumber

Jun 27, 2000 at 10:05 AM

Are you sure you use the Voodoo3 card?

Have you enumerated all drivers and chosen the voodoo 3 when you create the DirectDraw object or are you just passing NULL as the guid argument?

Edited by - Mr Cucumber on June 27, 2000 11:06:39 AM

simon_brown75

Jun 27, 2000 at 10:32 AM

Yeah, Voodoo 3 3000 AGP. I''m doing full device enumeration, using much the same method as shown in the SDK tutorials. Also I''m using the last DX7 retail drivers from 3dfx, not the betas. In all cases the larger textures produce a significant slow-down, although I''ve only been able to try the program on Voodoo 1, 2 and 3 cards so far.
Do I gather then that you don''t get the same problem at all with the V3? Also I can send you the code if it''ll help.

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