This patch is a major overhaul of nsBMPDecoder.
The patch improves the code in the following ways.
- It converts nsBMPDecoder to use StreamingLexer, which makes it much easier to
read.
- It adds a detailed comment about the BMP format at the top of
nsBMPDecoder.cpp.
- It fixes lots of inconsistent indenting.
- It moves |bihsize| from |mBFH| to |mBIH| to match the file format and common
sense. The avoids the need for the confusing LENGTH/INTERNAL_LENGTH
distinction.
- It renames most of the types in BMPFileHeader.h, so they have better names,
in StudlyCaps form, and within the new |bmp| namespace.
- It removes the BMP_HEADER_LENGTH struct and inlines its values directly into
the two places they were used.
- It removes the MOZ_LOG logging done on some of the failure cases. (Most
failure cases lacked logging so why bother with some?)
- It removes over 200 lines of code, despite the addition of the big format
comment.
The patch changes the way BMPs are decoded as follows.
- It adds stricter testing of the InfoHeader length, rejecting files with bad
values.
- It moves all header sanity checking that can lead to file rejection into the
metadata decode phase. (Previously, bpp/compression consistency checking did
not occur during a metadata decode.)
- It removes BMPINFOHEADER::ALPHABITFIELDS, which was (a) a weird WinCE-only
thing, and (b) we didn't actually allow it, and (c) we used the value 4
instead of 6(!).
- It rejects the previously-accepted compression==RLE4 && bpp=1 combination
because it doesn't make sense.
- It removes a fudge in RLE absolute mode handling that permitted one pixel too
many in a row but only if the row's width was odd(!)
- It now rejects a file with a negative gap between the color table and the
pixel data.
The patch leaves the following problems unaddressed.
- If bpp==32 we totally ignore compression==BITFIELDS and treat it like
compression=RGB.
- Transparency as specified in WinBMPv{4,5} isn't handled at all.
These will be fixed in follow-ups.
All these changes affect (for the better) the results of the following tests
that will be added in part 2:
- g/pal8v4.bmp
- g/pal8v5.bmp
- q/pal8os2sp.bmp
- q/pal8os2v2.bmp
- q/pal8os2v2-16.bmp
- b/badheadersize.bmp
- b/badpalettesize.bmp
- b/badrle.bmp
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