OK, I don't exactly want to stir up this hornets nest *again*, but a couple of things aren't entirely clear to me and I'd appreciate any clarifications.
As I understand it, the situation is as follows:
The S3TC algorithm is patented and therefore no-one can distribute an implementation of the algorithm without a licence from the patent holders.
S3TC decompression must be implemented in the hardware (otherwise what's the point), therefore hardware which uses S3TC can be assumed to have a valid licence to use the code, otherwise the patent owners would be down on the hardware manufacturers like the proverbial ton of bricks.
Patent law is actually more complicated than that. I'm not in a position to go into it, but it gets complicated when you have multiple components (i.e., software and hardware) working together to implement something.
As far as I'm aware, the main users of S3TC are modern games with their vast arrays of textures -- presumably such games come with the textures precompressed, or are able to compress them and cache the compressed textures themselves. Presumably again, the authors of the games have paid for a licence to use the S3TC algorithm from the patent holders.
Now, if an OpenGL application has a pile of textures already compressed with the S3TC algorithm, then I don't understand why the dri drivers can't simply offer the S3TC interfaces to the hardware, pass the compressed textures to the hardware and let the hardware get on with its licensed decompression of the textures as required. Likewise, if the OpenGL application passes compressed textures to the S3TC API then how it gets hold of the compressed textures in the first place is it's own responsibility -- the OpenGL API just passes them on.
Look at the ARB_texture_compression and EXT_texture_compression_s3tc specs again. You can specify uncompressed textures and have the driver compress the AND you can specify compressed textures and have the driver decompress them (to read them back into the application). For example, Quake3 can use the S3's vendor-specific extension (can't remember the name of it right now), but it does NOT have ANY textures pre-compressed. It expects the driver to do the work.
Can we add this to the FAQ, please?
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