Draw a stand-in for a font the file does not carry - #9
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A PDF need not carry the font its text is set in. Fourteen faces every reader is expected to have of its own, and in practice a file names any font at all and hopes. Of the 95 818 corpus pages that show text, 40 437 name a font the file does not carry and 38 663 carry none whatever. Drawing nothing for those is two pages in five with no text on them. Arimo, Tinos and Cousine are metric-compatible with Helvetica, Times and Courier — the same advances, glyph for glyph — so a stand-in gives the text the width it was meant to have even where the document gives no widths of its own, which one of the standard fourteen never does. For any other name the descriptor's flags say whether it wanted a serif, a sans or a typewriter. Only one weight of each is carried, so a bold is drawn by stroking the outline as well as filling it and an italic by leaning it over — what a typesetter calls a faux bold and a faux italic, and what every reader does with a face it has not got in the weight asked for. Symbol, the dingbats, composite fonts and Type 3 fonts are left alone. A composite font is addressed by glyph number and a stand-in's numbers are its own, so drawing one would put arbitrary letters on the page; and no face here carries Symbol's glyphs. Something is not better than nothing when the something is the wrong alphabet. Measured on the sample by hashing every page's pixels: 334 of 4 057 changed, 333 of them gaining ink. What this cannot do is invent a font's shapes: a page set in a face nobody has is a page set in something else, and it says so nowhere — which is what every reader does, and better than a blank page by the width of the text on it.
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A PDF need not carry the font its text is set in. Fourteen faces — four weights each of Helvetica, Times and Courier, plus Symbol and ZapfDingbats — every reader is expected to have of its own; and in practice a file names any font at all and hopes.
I counted. Of the 95 818 corpus pages that show text:
/WidthseitherDrawing nothing for those is two pages in five with no text on them.
What it draws instead
Arimo, Tinos and Cousine are metric-compatible with Helvetica, Times and Courier — the same advances, glyph for glyph — so a stand-in gives the text the width it was meant to have even where the document gives no widths of its own, which one of the standard fourteen never does. (Tinos was not bundled until fonts#10;
HasWidthis pdffont#2.)For any other name, the descriptor's flags say whether it wanted a serif, a sans or a typewriter.
Only one weight of each is carried, so a bold is drawn by stroking the outline as well as filling it and an italic by leaning it over — a faux bold and a faux italic, which is what every reader does with a face it has not got in the weight asked for.
What it leaves alone
Symbol, the dingbats, composite fonts and Type 3 fonts. A composite font is addressed by glyph number and a stand-in's numbers are its own, so drawing one would put arbitrary letters on the page; and no face here carries Symbol's glyphs. Something is not better than nothing when the something is the wrong alphabet.
Measured
334 of 4 057 pages changed, 333 of them gaining ink — and this sample is arXiv figures; a corpus of documents would show far more. The one page that lost any lost 0.17% of a very inky page. Robustness unchanged: 4 108 pages, no panics, six blank.
What this cannot do is invent a font's shapes. A page set in a face nobody has is a page set in something else, and it says so nowhere — which is what every reader does, and better than a blank page by the width of the text on it.
100% statement coverage.