Hi Stefan, thanks for your answer. I've checked the nvidia texture tools but, sadly, I think it's impossible to use them in wine: while they have c bindings, those bindings lack the essential function nvttSetOutputOptionsOutputHandler(NvttOutputOptions * outputOptions, nvttOutputHandler outputHandler, nvttImageHandler imageHandler) (commented out in the headers), so the output can only be written to a file. What about going the mesa way, where the drivers aren't linked with any s3tc library, but load it at runtime if it is present? Any idea is welcome.