All the logic is exactly the same as for x2 upsampling, so this commit
essentially boils down to adding arrays for default weights and the
logic to select the correct array.
This is something I missed when I ported the JPEG XL decoder to the new
plugin interface (decoding the header at creation). First sorry because
that's entirely my fault, second sorry because a test should have caught
that.
Instead of rejecting them, we truncate each value to 8 bits. This is
clearly a hack, but given the lack of support of variable bit-depth in
`Bitmap` this is the only sensible change.
This allows us to display "Iceberg" on https://jpegxl.info/art/.
JPEG-XL is a new image format standardized by the same committee as the
original JPEG image format. It has all the nice feature of recent
formats, and great compression ratios. For more details, look at:
https://jpegxl.info/
This decoder is far from being feature-complete, as it features a grand
total of 60 FIXMEs and TODOs but anyway, it's still a good start.
I developed this decoder in the Serenity way, I just try to decode a
specific image while staying as close as possible to the specification.
Considering that the format supports a lot of options, and that we
basically support only one possibility for each of them, I'm pretty sure
that we can only decode the image I've developed this decoder for.
Which is:
0aff 3ffa 9101 0688 0001 004c 384b bc41
5ced 86e5 2a19 0696 03e5 4920 8038 000b
