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LibPDF: Don't crash on fixed-width type 1 fonts that use /MissingWidth
Type 1 fonts usually have a m_font_program and no m_font -- they only have m_font if we're using a replacement font for the fonts that were built-in to PDFs before Acrobat 4.0 (and must still work to show existing files). However, SimpleFont::get_glyph_width() used to always return a float, which in Type1Font was only implemented if m_font was set. Per spec, we're supposed to just use /MissingWidth for fonts that are missing an entry in the descriptor's /Width array. However, for built-in fonts, no explicit /Width array is needed (PDF 1.7 spec, Appendix H.3, 5.5.1). So if we just always use /MissingWidth, then PDFs that use a built-in font draw all their text on top of each other (e.g. 000333.pdf from stillhq.com-pdfdb). So change get_glyph_width() to return Optional<float>, return it only in Type1Font if m_font is set, and use MissingWidth if it isn't set. That way, replacement fonts still return a width, and real fonts that are supposed to have /Width and use /MissingWidth for missing entries do what they're supposed to too, instead of crashing. From 20 (6%) to 16 (5%) crashes on the 300 first PDFs, and from 39 (7.8%) to 31 (6.2%) on the 500-random PDFs test.
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6 changed files with 12 additions and 8 deletions
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@ -53,8 +53,10 @@ PDFErrorOr<Gfx::FloatPoint> SimpleFont::draw_string(Gfx::Painter& painter, Gfx::
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float glyph_width;
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if (auto width = m_widths.get(char_code); width.has_value())
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glyph_width = font_size * width.value() / 1000.0f;
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else if (auto width = get_glyph_width(char_code); width.has_value())
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glyph_width = width.value();
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else
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glyph_width = get_glyph_width(char_code);
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glyph_width = m_missing_width;
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draw_glyph(painter, glyph_position, glyph_width, char_code, paint_color);
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