It shouldn't be too hard to implement probably. You'd need to implement the CompressedTexImage2D and CompressedTexSubImage2D functions (should be straight-forward), and adapt the ChooseTextureFormat function. The radeon deals with compressed textures pretty much the same way as with other textures, you'd just need to set the texture format correctly, and make sure the alignment is correct - the savage might be a bit more complicated, I have no idea how the tiling code works. (As a side note, the savage include files seem to suggest the chip also supports some luma-based s3tc compressed textures. Interesting - I don't think there's an OGL extension to support this though, but if I'd have to guess I'd think that luma values use the same encoding scheme as alpha values in DXT5.)As for the texture compression stuff, I have never tried it myself. Roland Scheidegger has been working on this for the Radeon and r200 drivers. He can probably give you more information about what is needed and how it works. I'm not sure how much work it would take to integrate this into the savage driver. You'd at least have to modify savageChooseTextureFormat and write the texture tiling and upload code for it. The current code is only tested for non-compressed textures.
You can find the radeon/r200 patch here:
http://marc.theaimsgroup.com/?l=dri-devel&m=107527085116767&w=4
you probably don't want to implement the forced texture compression though, it's not OGL-spec compliant and problematic anyway (dynamic textures), if you drop it you can also scratch some of the mesa changes (since with the forced compression mesa needs to check texture format after the ChooseTextureFormat function, not before).
Just a warning: if you intend to ship s3tc enabled products, your legal department should check if that's ok. You might need a license to do so, or maybe not if you don't implement software encoding/decoding (which would make your implementation non-compliant to GL_EXT_texture_compression_s3tc, but for only displaying pre-compressed textures that's enough - unless you hit a software fallback at least). That's of course the reason the newer versions of my patch use an external library, though without the desired result (which was to make it possible to integrate the patch into regular mesa)...
Roland
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