bugThe FreeType Project - Bugs: bug #24357, Autohinter poorly hints U+0119 ę...

 
 

bug #24357: Autohinter poorly hints U+0119 ę in DejaVu Sans

Submitted by:  Marcin Kowalczyk <qrczak>
Submitted on:  Tue 23 Sep 2008 04:19:41 PM UTC  
Votes:  50  
 
Severity: 3 - NormalItem Group: Incorrect behaviour
Status: ConfirmedPrivacy: Public
Assigned to: David Turner <freetype>Open/Closed: Open
Planned Release: None

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Fri 29 Oct 2010 03:51:21 PM UTC, comment #5:

Although this bug is less important since true type bytecode is enabled by default, I still tried to investigate this issue.

I compiled freetype without truetype bytecode interpreter and tracked down the differences between the two glyphes. I discovered that in af_latin_hint_edges, an anchor edge is computed in the first part of the function. And it is different for the e and the ę (for the ę, I think it's part of the ogonek). This probably happens because freetype uses the first blue edge encountered as an anchor. Then, when snapping the horizontal bar, org_pos, computed as anchor->pos + ( edge->opos - anchor->opos ) is not the same.

I could not investigate more nor try working on a patch because I failed to understand algorithm behind anchor edge (what is it and how does it work?). I also failed to get the big picture of blue edge stuff. Reading "Real-Time Grid Fitting of Typographic Outlines" didn't help.

arno <arenevier>
Sat 03 Oct 2009 09:14:00 PM UTC, comment #4:

Yes, this bug doesn't depend on a font
I produced screenshots (Ubuntu 9.04) with different fonts (some chars got replaced due to the missing glyphs in the char table, but it's easy to see which ones)

i quickly tested Arial, Verdana, DejavuSans, DejavuSerif, TrebuchetMS, NimbusSans and Georgia using Ubuntu font configuration options - ę is broken at some sizes in the 10-14 range in every case. Horizontal line is 1px off, this sometimes happens to the capital letter (Ę) too albeit less often.

While looking carefully at the DejavuSans I noticed that the base shape of the e glyph is distorted when there is some modifier at the bottom (dots, ogonek, whatever). Modifiers above seem not to produce any unwanted effects.
I couldn't check my findings with other fonts because usually they don't cover these obscure e derivatives.

This issue may not appear serious, because only ę is common enough to be included in a common font, but I am sure there would be problems with all unicode fonts having extensive set of glyphs that cover other e's with modifiers. I just don't understand why e is so magic when combined with other stuff :)

This issue may not appear serious but it's annoying to say the least. It's a vowel you can often see multiple times in a single sentence in Polish (for example in the simple sentence "I will love you" you get it 3x) and you literally can't find even single font that scales well in the 10-14 range (especially sansserif type).

(file #18807, file #18808, file #18809, file #18810)

MKK <vaphell>
Thu 21 May 2009 08:35:44 AM UTC, comment #3:

I've also noticed that this doesn't depend on font. I've checked with Liberation font (17pt) and there is the same problem there.

It looks like autohinter fails with this U+0119 composite glyph. Somehow it doesn't work well for it.

Tomasz Kalkosiński <pppspoonman>
Tue 12 May 2009 10:34:09 AM UTC, comment #2:

I confirm that. I've also submitted bug here: http://bugs.freedesktop.org/show_bug.cgi?id=21664 .

David, can you please take a look at this? Thanks in advance.

Tomasz Kalkosiński <pppspoonman>
Sun 05 Oct 2008 07:08:40 AM UTC, comment #1:

[Using DejaVu Sans 2.26]

I can confirm this, using ftstring of the current CVS.
Apparently, the computation of the local constraints are too aggressive, influencing the whole glyph.

David, can you check this?

Werner LEMBERG <wl>
Project Administrator
Tue 23 Sep 2008 04:19:41 PM UTC, original submission:

With autohinting (“slight hinting” in Gnome settings), in DejaVu Sans and Sans Mono, ‘e’ and ‘ę’ at some sizes have the horizontal bar at different heights; ‘e’ is fine, ‘ę’ is ugly.

In the font the ę glyph is made of two subglyphs: ‘e’ + ogonek, so this is not the fault of the font.

Marcin Kowalczyk <qrczak>

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach File(s):
   
   
Comment:
   

Attached Files
file #18810:  trebuchet_ms_14.png added by vaphell (3kB - image/png)
file #18809:  verdana_14.png added by vaphell (4kB - image/png)
file #18808:  dejavu_sans_13.png added by vaphell (3kB - image/png)
file #18807:  arial_12.png added by vaphell (3kB - image/png)
file #18172:  liberation.jpg added by pppspoonman (24kB - image/jpeg - Liberation autohinter failure.)
file #16553:  eogonek.png added by qrczak (25kB - image/png - Firefox screenshot and its HTML source.)
file #16554:  eogonek.html added by qrczak (2kB - text/html - Firefox screenshot and its HTML source.)

 

Depends on the following items: None found

Items that depend on this one: None found

 

Carbon-Copy List
  • -unavailable- added by arenevier (Posted a comment)
  • -unavailable- added by vaphell (Updated the item)
  • -unavailable- added by pmw
  • -unavailable- added by pppspoonman (Posted a comment)
  • -unavailable- added by pppspoonman (Voted in favor of this item)
  • -unavailable- added by wl (Posted a comment)
  • -unavailable- added by qrczak (Submitted the item)
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    Follow 11 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Sat 03 Oct 2009 09:14:00 PM UTCvaphellAttached File-=>Added trebuchet_ms_14.png, #18810
      Attached File-=>Added arial_12.png, #18807
      Attached File-=>Added dejavu_sans_13.png, #18808
      Attached File-=>Added verdana_14.png, #18809
    Tue 18 Aug 2009 10:55:22 AM UTCpmwCarbon-Copy-=>Added -unavailable-
    Thu 21 May 2009 08:37:28 AM UTCpppspoonmanAttached File-=>Added liberation.jpg, #18172
    Tue 12 May 2009 10:32:39 AM UTCpppspoonmanCarbon-Copy-=>Added pppspoonman
    Sun 05 Oct 2008 07:08:40 AM UTCwlStatusNone=>Confirmed
      Assigned toNone=>freetype
    Tue 23 Sep 2008 04:19:41 PM UTCqrczakAttached File-=>Added eogonek.png, #16553
      Attached File-=>Added eogonek.html, #16554

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