How to convert BC7 to ASTC directly and fastly?

Question

I have prepared-well BC7 tetxure, how to convert it to astc format (e.g., ASTC_12x12) directly? Not decompress BC7 -> compress ASTC, It's too slow.

Is there any algorithm or tool that can convert BC7 directly to standard ASTC format? No high image quality required

Answer 1

There are some transcoding tools from Khronos which compress to a UASTC intermediate format, which can be transcoded efficiently into BC7 or ASTC on the target device once you know what you need. The bitrate choices are somewhat limited - transcoding needs the destination formats to have broadly similar compression ratios - so the most direct conversion would be to a 4x4 encoding which is 8bpp in both formats.

I'm not aware of any tools that do direct conversion from BC7 to ASTC.