When I added mp_regular_imgfmt, I made the chroma subsampling use the
actual chroma division factor, instead of a shift (log2 of the actual
value). I had some ideas about how this was (probably?) more intuitive
and general. But nothing ever uses non-power of 2 subsampling (except
jpeg in rare cases apparently, because the world is a bad place).
Change the fields back to use shifts and rename them to avoid mistakes.
This tests the RGB repacker code in zimg, which deserves to be tested
because it's tricky and there will be more formats.
scale_test.c contains some code that can be used to test any scaler. Or
at least that would be great; currently it can only test repacking of
some byte-aligned-component RGB formats. It should be called
repack_test.c, but I'm too lazy to change the filename now.
The idea is that libswscale is used to cross-check the conversions
performed by the zimg wrapper. This is why it's "OK" that scale_test.c
does libswscale calls.
scale_sws.c is the equivalent to scale_zimg.c, and is of course
worthless (because it tests libswscale by comparing the results with
libswscale), but still might help with finding bugs in scale_test.c.
This borrows a sorted list of image formats from test/img_format.c, for
the same reason that file sorts them.
There's a slight possibility that this can be used to test vo_gpu.c too
some times in the future.
