Similarly like pixel size is stored in uncompressed images, block size
makes it possible to perform size checks on passed data, slice the images
and so on. It only took over a decade to get that done.
The block properties coming from CompressedPixelStorage are currently
expected to be either not set at all or exactly match what's stored in
the image for given format. The PixelStorage will get eventually
deprecated in favor of a simpler and more flexible representation, but
that's another big chunk of work so it's first done like this.
The GL library tests currently blow up on various assertions and it
isn't yet updated to make use of the known format properties instead of
querying them from GL. That'll be done in the following commits.
In case of compressed images the tests were absolutely insufficient, as
they were always verifying just a single block, and thus they passed
even though the actual calculation was wrong in several ways.
And then the occupiedCompressedImageDataSize() wasn't tested at all,
even though it should return something completely different from the
function it delegates to.
Fixes to both in the next commit.
Vladimír Vondruš