[luatex] Strange behavior with fonts.

Paul Isambert zappathustra at free.fr
Wed Apr 20 15:29:48 CEST 2011

Additional information (don't know why I didn't spot it before):

I had set the expansion step to 30, the same value as shrink and 
stretch, pretty stupidly. Anyway, if I put it to something lower, I 
apparently have to increase the glyphs' expansion_factor for the problem 
to show up. For instance, with step = 10, expansion_factor should be at 
least 1214.

(Also, my LuaTeX is v0.66 rev 4136. And I had left a useless inspection 
of post_linebreak_filter in the file I've sent, sorry for that.)


Le 20/04/2011 15:14, Paul Isambert a écrit :
> Hello there,
> I think I've found a bug, but since I'm still a bit uncomfortable with 
> fonts and I can't reproduce the problem with luaotfload (haven't tried 
> very hard, though), I think it wise to ask knowledgeable people before 
> polluting the bug tracker.
> The problem is entirely contained in the attached files.
> The Lua code is an extremely blunt font loader, as minimal as possible 
> while still displaying the problem; it is also extremely stupid: on 
> first use, it sets the glyph to their Unicode slots; the second time, 
> it puts small caps in the slot of the lowercase letters (it is meant 
> to spot Minion's small caps). In other words, after:
> \font\fontone=MinionPro-Regular.otf at 10pt
> \font\fonttwo=MinionPro-Regular.otf at 10pt
> \fontone writes normally, while \fonttwo writes in small caps. That's 
> the way I use a font with small caps (I suppose that's the only way, 
> unless you change glyphs in callbacks). I've used Minion because it is 
> distributed freely with Adobe Reader.
> Now, if you look at the PDF or compile the source, you can see that 
> it's all wrong; sizes are at random and the paragraph is like 
> raggedright. If \fonttwo isn't loaded, everything is fine; otherwise, 
> disaster, even though \fonttwo is loaded /after/ the paragraph has 
> been built, which seems to indicate something has gone wrong when 
> outputting to PDF (of course the problem also shows up when \fonttwo 
> is loaded before the paragraph). Judging from what I can read in the 
> uncompressed PDF file when comparing to an unproblematic file, spaces 
> between characters are all wrong (I don't know where those spaces come 
> from, by the way; there are no font kerns with this fontloader).
> A few remarks about the behavior:
> - It depends on font expansion; without \pdfadjustspacing, everything 
> is fine.
> - It also depends on the value given to the glyphs' "expansion_factor" 
> field; if 484 or higher, it goes wrong; if 483 or lower, everything is 
> fine. The value of that threshold depends on the font (e.g. it is 909 
> for Chaparral).
> - If there is a one-line paragraph before the first paragraph, 
> everything is fine.
> - If there is a page break before the second font is loaded, again 
> everything is fine.
> - The fonts should be loaded at the same size; if e.g. \fonttwo is 
> 10.1pt, the problem vanishes.
> Did I do anything wrong or is that a patented bug? (Actually, I think 
> that even if I did anything wrong the behavior is so strange that it's 
> very probably a bug anyway.)
> Best,
> Paul
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