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Tests/LibGfx: Add a test jbig2 file using TPGDON
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"TPGD" is short for "Typical Prediction for Generic Direct coding",
and the "ON" bit turns it on. In this mode, before decoding a line,
we decode a single bit first that controls if the current line is
just a copy of the previous line. If so, the line's pixels aren't
encoded, the decoder just copies the previous line.

I created this by running

    jbig2 -i Tests/LibGfx/test-inputs/bmp/bitmap -f bmp \
        -o bitmap -F jb2 -ini tpgdon.ini

where tpgdon.ini contained:

    -Gen -Seg 1
    -Gen -Param -TpGDon 1

See previous commits in this directory for details on the `jbig2` tool.

Sadly, the TPGDON writing path in `jbig2` wasn't implemented yet,
so I had to add this. See the PR that added this commit for my
local diff to `jbig2`.

I'm somewhat confident that my change to `jbig2` (and hence the
image added in this commit) is correct because:

1. `jbig2` succeeds in converting this file to a bmp file,
   while it failed without my patch (the decoding codepath in
   `jbig2` does have TPGDON support)

2. Other pdf viewers display the output of
   `Meta/jbig2_to_pdf.py -o foo.pdf path/to/bitmap-tpgdon.jbig2 399 400`
   the same way we do
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nico committed Mar 16, 2024
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