What happened to 3Dc, ATI’s texture compression system for normal maps?
AFAIK there was an extension for it in some of their drivers, there’s ATI’s whitepaper, but it seems there’s no extension specification.
Why did ATI kill 3Dc? Did they?
AFAIK, both are verbatim copies of the alpha channel compression used in DXT5. The NVidia extension also supports LATC1 as well, for when you only want to compress one component.