...and add a test case that shows why it's incorrect.
If one dimension is 2^n + 1 and the other side is just 1, then the
topmost node will have 2^n x 1 and 1 x 1 children. The first child will
have n levels of children. The 1 x 1 child could end immediately, or it
could require that it also has n levels of (all 1 x 1) children. The
spec isn't clear on which of the two alternatives should happen. We
currently have n levels of 1 x 1 blocks.
This test case shows that a VERIFY we had was incorrect, so remove it.
The alternative implementation is to keep the VERIFY and to add a
if (x_count == 1 && y_count == 1)
level = 0;
to the top of TagTreeNode::create(). Then we don't have multiple levels
of 1 x 1 nodes, and we need to read fewer bits.
The images in the spec suggest that all nodes should have the same
number of levels, so go with that interpretation for now. Once we can
actually decode images, we'll hopefully see which of the two
interpretations is correct.
(The removed VERIFY() is hit when decoding
Tests/LibGfx/test-inputs/jpeg2000/buggie-gray.jpf in a local branch that
has some image decoding implemented. That file contains a packet with
1x3 code-blocks, which hits this case.)
Most JPEG2000 files put the codestream in an ISOBMFF box structure
(which is useful for including metadata that's bigger than the
~65k marker segment data limit, such as large ICC profiles), but
some files just store the codestream directly, for example
https://sembiance.com/fileFormatSamples/image/jpeg2000/balloon.j2c
See https://www.iana.org/assignments/media-types/image/j2c for the
mime type.
The main motivation is to be able to use the test data in J.10 in
the spec as a test case.
A tag tree is a data structure used for deserializing JPEG2000
packet headers.
We don't use them for anything yet, except from tests.
The implementation feels a bit awkward to me, but we can always polish
it later.
The spec thankfully includes two concrete examples. The code is
correct enough to pass those -- I added them as test.
For text, we always ended up with a leading \0 byte (on little-endian),
which prints as nothing. Since that's the only thing we do with this
data, no actual behavior change.
We don't do anything with this (except log the contents if
JPEG2000_DEBUG is 1).
The motivation is that we now decode all marker segments that are
used in all JPEG2000 files I've seen so far, allowing us to make
remaining unknown marker types fatal.
The T.800 spec says there should only be one 'colr' box, but the
extended jpx file format spec in T.801 annex M allows having multiple.
Method 2 is a basic ICC profile, while method 3 (jpx-only) allows full
ICC profiles. Support that.
For the test, I opened buggie.png in Photoshop, converted it to
grayscale, and saved it as a JPEG2000, with "JP2 Compatible" checked
and "Include Transparency" unchecked. I also unchecked "Include
Metadata", and "Lossless". I left "Fast Mode" checked and the quality
at the default 50.
JPEG2000 is the last image format used in PDF filters that we
don't have a loader for. Let's change that.
This adds all the scaffolding, but no actual implementation yet.
