Wednesday, August 22, 2007

Texture Compression Is Your Friend

Try this experiment: take three screen-shots (use ctlr-; to get a stable, clear view), with these settings:
  1. Extreme res, with tex compression
  2. Extreme res, without tex compression
  3. Very high res, without tex compression
Now consider the effect on VRAM. Each time you go down a texture resolution level, tex sizes are cut in half, and you cut VRAM use by a factor of 4.

If you use texture compression, you cut VRAM use by a factor of 4 for textures with alpha and a factor of 6 for textures without alpha. (Some textures are unaffected because they are internally marked as "never compress".)

Now look at your visual results. I would argue two things:
  • At extreme res, turning off texture compression doesn't make the image a whole lot nicer. (It does make the machine a whole lot slower!)
  • Texture compression is a lot nicer than going down a res level.
I suspect that if your machine can't handle extreme res, you can get similar results running the whole experiment down one notch.

I think that almost everyone who has a limited machine is running with texture compression these days - we default with it on and it helps fps. I would only argue that any users who are running with a huge machine and compression off might consider turning it back on. It doesn't hurt much and it does make the machine run faster.

(Even if you have a ton of VRAM, X-Plane can be limited by how fast texture data transfers from VRAM to the GPU, within the card. Texture compression helps this.)

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