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LibPDF: Ignore unknown CFF operators

Browse source 
https://adobe-type-tools.github.io/font-tech-notes/pdfs/5177.Type2.pdf
says "The behavior of undefined operators is unspecified." but
https://learn.microsoft.com/en-us/typography/opentype/spec/cff2
says "When an unrecognized operator is encountered, it is ignored and
the stack is cleared."

Some type 0 CIDFontType0C fonts (i.e. CID-keyed non-OpenType CFF fonts)
depend on the latter, even though they're governed by the former spec.

Fixes rendering of text in 0000521.pdf (e.g. page 10 or 5). The font
there has a bunch of 0 opcodes for some reason.
This commit is contained in:
Nico Weber 2024-02-07 21:44:28 -05:00 • committed by Sam Atkins
parent 9f50ad9208
commit dde11e1757
1 changed files with 10 additions and 1 deletions
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11
Userland/Libraries/LibPDF/Fonts/Type1FontProgram.cpp
View file

@ -716,7 +716,16 @@ PDFErrorOr<Type1FontProgram::Glyph> Type1FontProgram::parse_glyph(ReadonlyBytes
default:
dbgln("Unhandled command: {}", v);
return error("Unhandled command");
// https://adobe-type-tools.github.io/font-tech-notes/pdfs/5177.Type2.pdf
// says "The behavior of undefined operators is unspecified." but
// https://learn.microsoft.com/en-us/typography/opentype/spec/cff2
// says "When an unrecognized operator is encountered, it is ignored and
// the stack is cleared."
//
// Some type 0 CIDFontType0C fonts (i.e. CID-keyed non-OpenType CFF fonts)
// depend on the latter, even though they're governed by the former spec.
state.sp = 0;
break;
}
}
}