LibGfx/JBIG2Writer+Tests/LibGfx: Add support for files in random access organization #26407
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We now store each segment's encoded data on the encoding context. This will be useful for implementing writing files in the random access organization, and it will hopefully also be useful in cases where we need to partially decode the file we're about to write (for example when refining whole text or halftone regions, or when refining the current page). This requires a few more copies than before, but it's small amounts of data. `compile.sh` time does not change measurably with this. No behavior change.
Files in random access organization first store all segment headers, followed by all segment data. (In contrast, the usual sequential organization writes each segment's header and data in one piece.) For that reason, files in random access organization *must* end with an end_of_file segment, while it's optional for files in sequential organization. Almost all jbig2 decoders in existence can only read jbig2 data when it's part of a PDF. JBIG2 data in a PDF is in the "embedded" organization, which is like the sequential organization without the file header. That means it's a bit difficult to test if random access files are correct. Having said that, `jbig2dec` decodes the files we're writing fine.
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Files in random access organization first store all segment headers,
followed by all segment data. (In conctrast, the usual sequential
organization writes each segment's header and data in one piece.)
For that reason, files in random access organization must end
with an end_of_file segment, while it's optional for files in sequential
organization.
Almost all jbig2 decoders in existence can only read jbig2 data when
it's part of a PDF. JBIG2 data in a PDF is in the "embedded"
organization, which is like the sequential organization without the file
header. That means it's a bit difficult to test if random access files
are correct. Having said that,
jbig2decdecodes the files we'rewriting fine.