Why don't modern GPUs support palettized textures

Andy W · 2015-12-19T01:46:40

I'm just removing support for palettized textures from an engine at the moment as we're unlikely to release a game on any hardware that supports them. It got me thinking though... why have palettized textures lost so much popularity that they're effectively non-existent these days? I get that block compression is going to produce better quality and size results in typical cases, and I get that you could cobble together your own inefficient texture LUT support in a fragment shader. But it seems to me that there are some textures where a 256 colour 8888 palette would do a much better job than, e.g. a DXT5 or a PVRTC4. There are also some cases where palette switching tricks would be a handy memory saving trick, e.g. for applying team colours to a sprite. And GPU support for palettization seems simple (from my naive standpoint as a user of GPUs rather than a designer of one!) a 256 colour 32-bit palette would only take 1K of texture cache, texture unit hardware copes with far more complex encodings than a straightforward lookup table. I guess I understand why texture palettes fell out of vogue, I don't understand why they are completely dead. I think I'm missing something.

Graphics and GPU Programming Programming

Started by C0lumbo December 18, 2015 08:12 AM

10 comments, last by Infinisearch 8 years, 4 months ago

samoth

9,833

December 18, 2015 05:59 PM

A 64x64 texture would probably gain more by using palettes over BC1 compression. But as the resolution goes higher; the compressed version will almost always win. There's no way a 2048x2048 palette texture would be better than a compressed version.

Well, it would be better if it encodes for example the 16 customizable colors (in 16 shades each) that make up a character's personalized clothes, and you draw 300 characters each with individually colored clothes, only indexing into a different part of the palette for each, and they all use the exact same texture.

But... that is admittedly a very contrieved case which not a lot of people will need every day (and if they need it, they can implement it in the shader!).

Dingleberry

924

December 18, 2015 10:59 PM

That is why they need to introduce a 'texture shader' stage. A shader stage that would feed unfiltered texels into the texture cache, which a shader could then sample from.

We don't necessarily need a new stage for that, access to groupshared (LDS) memory outside of compute shaders would go a long way

I'd be really happy with either :(

Infinisearch

3,058

December 19, 2015 01:46 AM

Didn't hardware palettized textures also have dedicated memory for the lookup table? That would help out with performance as well.

We don't necessarily need a new stage for that, access to groupshared (LDS) memory outside of compute shaders would go a long way

Trying to make async shaders harder to implement I see.

-potential energy is easily made kinetic-

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