Basis non-RDO BC7 benchmark

This graph shows the performance of ispc_texcomp at each of its supported opaque profiles (from ultrafast to slow) vs. Basis's non-RDO BC7 encoder at various settings. I haven't decided on the settings to use for each of our profiles yet, which is why I'm generating graphs like this.

For reference, BC1 non-perceptual gets ~36.92 dB on this test set, so even just mode 6 BC7 (the first data points on the bottom left) is superior to BC1's quality.

Basis non-RDO BC7 also has a "ultra" profile which is ~.49 dB better than ispc_texcomp's slow profile (its highest quality mode), but you pay a steep price in encoding time (959 secs vs. ~350 secs for ispc_texcomp's slow profile). In this mode Basis is even better than the reference BC7 encoder in NVidia's NVTT (but we're ridiculously faster):

Basis BC7 ultra:   953.2 secs   47.255552 dB
Basis BC7 slow:    365.5 secs   47.162389 dB
NVTT:              28061.9 secs 47.141580 dB
ispc_texcomp slow: 353.6 secs   46.769749 dB

The leftmost bottom samples are mode 6 only (ispc_texcomp's ultrafast profile). We are 19% faster at slightly higher quality here.

Basis non-RDO BC7 supports a powerful perceptual mode which I'll benchmark tomorrow. In this mode we kinda wreck ispc_texcomp at the same Luma PSNR (but to be fair ispc_texcomp doesn't support a perceptual mode at all, which is a serious deficiency).