bugThe FreeType Project - Bugs: bug #44241, Font with overlaping paths...

 
 

bug #44241: Font with overlaping paths autohinted into nothing.

Submitted by:  bungeman <bungeman>
Submitted on:  Fri 13 Feb 2015 08:28:03 PM UTC  
 
Severity: 3 - NormalItem Group: None
Status: FixedPrivacy: Public
Assigned to: Werner LEMBERG <wl>Open/Closed: Closed
Planned Release: 2.6.0

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Tue 03 Mar 2015 10:26:02 AM UTC, comment #2:

Thanks for the report; this is now fixed in git.

This font lies, as you've correctly noted, but it was easy to work around this very problem by rejecting glyphs that have less than three points.

Werner LEMBERG <wl>
Project AdministratorIn charge of this item.
Fri 20 Feb 2015 06:51:53 PM UTC, comment #1:

I think I know what is happening now. I went and fixed the issues with the font outlines overlapping, and generally fixed things up, but the issue persisted. That's when I noticed that this font is being subset by some means which, instead of removing characters and glyphs, is instead setting unused glyphs to trivial paths. So in this font A-Z and b-z and a number of others are all 'empty glyphs', where by empty I mean 'have two points, one on top of the other'.

As a result, it appears the autohinter is trying to find the features of these degenerate glyphs and decides (probably correctly, given the information in the font) that all of the features are of zero width, and so hints that way. Not sure if this should be detected of not.

bungeman <bungeman>
Fri 13 Feb 2015 08:28:03 PM UTC, original submission:

This was an issue originally reported against Chromium, see https://crbug.com/394373 . The webfont in question there can currently be found at http://www.ebooksystem.net/downloads/tuned/Tuned/Fonts/NumbersRedbird.ttf .

Loading this font into ftview with any size 8pt or greater when forcing on autohinting (the 'f' key) causes most glyphs in this font disappear. Taking a look in FontForge, it reports a number of places where this font self intersects, mostly at places where the path doubles back on itself (usually by 1 FUnit) or the path has multiple consecutive points at the same location.

I realize that this font isn't up to spec, but it seems that it would be helpful if the autohinter realized that things weren't going to work out and there were some sort of fallback. When this happens, the FT_Render_Glyph call returns 0, so I don't think even an error is being propagated out.

bungeman <bungeman>

 

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  • -unavailable- added by wl (Posted a comment)
  • -unavailable- added by bungeman (Submitted the item)
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    Follow 4 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Tue 03 Mar 2015 10:26:02 AM UTCwlStatusNone=>Fixed
      Assigned toNone=>wl
      Open/ClosedOpen=>Closed
      Planned ReleaseNone=>2.6.0

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