[maxp] Attempt to improve fixup of bad 'maxp' version numbers. #267
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khaledhosny
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Nov 11, 2023
If the version number is not explicitly v0.5 (0x00005000), try to read it as v1.0. (The version field will be corrected to one of the valid versions during serialization.) This handles cases where the table was intended to be v1.0 (for a font with TrueType data), but the version field was set incorrectly (e.g. to 0x00000100, as seen in mozilla/pdf.js#16839). Also make the max_zones fixup more general, as the example font from the above issue has max_zones=512(!). Correcting it to 2 should be harmless.
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If the version number is less than 0x00010000 (e.g. an example reported at mozilla/pdf.js#16839 apparently has 0x0100), it will be treated as version 0.5 and only the num_glyphs field is kept.
However, this can prevent the font working on Windows, which apparently requires the full version 1.0 maxp table for truetype fonts.
So if the version number was bad, but there is in fact enough data to parse as version 1.0, let's try correcting it to 1.0 rather than 0.5.
(Test not included because the example in the issue appears to be a derivative of a proprietary font.)