bugThe FreeType Project - Bugs: bug #23537, When hintstyle=hintslight,...


bug #23537: When hintstyle=hintslight, character is rendered incorrectly (tilde as macron)

Submitted by:  Simos Xenitellis <simos>
Submitted on:  Wed 11 Jun 2008 01:19:26 AM UTC  
Severity:  3 - Normal Item Group:  Incorrect behaviour
Status:  Confirmed Privacy:  Public
Assigned to:  None Open/Closed:  Open
Planned Release:  None

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Sat 14 Jan 2017 08:57:50 AM UTC, comment #10:

Look here


Werner LEMBERG <wl>
Project Administrator
Sat 14 Jan 2017 03:59:37 AM UTC, comment #9:

I've just looked at DejaVu and Liberation fonts. I do not see the problem any more. Can somebody please show how to reproduce it with FreeType 2.7.1?

Alexei Podtelezhnikov <podtelez>
Project Member
Fri 13 Jan 2017 08:58:53 PM UTC, comment #8:

We don't hint AF_DIR_NONE.

If you have a sinus-like curve, let the vertical maximum correspond to value x, and the minimum to value y. Normal fonts have horizontal segments (in the auto-hinter sense) at the extremum values, which results in two `edges'. If |x-y| is less than a certain value, the auto-hinter makes x=y – and this is what should be avoided for tilde-like characters, but what you would expect for larger structures (cf. the Type 1`flex' feature).

Werner LEMBERG <wl>
Project Administrator
Fri 13 Jan 2017 03:17:42 PM UTC, comment #7:

I would argue otherwise. This tilde segments are not horizontal, AF_DIR_NONE should never be hinted, because it removes features. What is so special here?

Alexei Podtelezhnikov <podtelez>
Project Member
Fri 13 Jan 2017 07:42:25 AM UTC, comment #6:

Yes. However, in most situations you want the current behaviour of the auto-hinter to flatten such wiggles. As mentioned earlier, you need `character knowledge' to improve that. Right now I'm brooding on a possible implementation, but please don't expect quick results :-)

Werner LEMBERG <wl>
Project Administrator
Fri 13 Jan 2017 04:33:57 AM UTC, comment #5:

This situation is reminiscent of bug 41334 but in the vertical direction, of course. The hinter is overzealous. If the tilde remained blurry, no one would complain.

Alexei Podtelezhnikov <podtelez>
Project Member
Wed 02 Nov 2016 06:17:43 AM UTC, comment #4:

I would have to add `character knowledge' to FreeType's auto-hinter For the specific case, FreeType would have to know that the character is a tilde, then it could apply more vertical scaling at small sizes before hinting so that the glyph's wiggle stayed visible.

In 2008, there was no HarfBuzz support for FreeType, which meant that getting such information was impossible. This has changed meanwhile, so a fix could be done as outlined above.

However, I currently don't have plans to implement that, but maybe there are volunteers...

Or maybe there are better suggestions?

Werner LEMBERG <wl>
Project Administrator
Tue 01 Nov 2016 10:40:49 PM UTC, comment #3:

bug 49312 was duped to this.

Jungshik Shin <jungshik>
Mon 03 Aug 2015 08:57:37 AM UTC, comment #2:

This bug also manifests in letters like ã/õ (a/o tilde) and occasionally even with the ~ character alone. DejaVu, Liberation, Droid (Sans and Mono) seem to show this around size 10.

Wed 11 Jun 2008 08:17:50 AM UTC, comment #1:

See also discussion at dejavu mailing list,

Simos Xenitellis <simos>
Wed 11 Jun 2008 01:19:26 AM UTC, original submission:

When the following precise conditions apply, a character is rendered incorrectly. A tilde (perispomeni) is shown as macron (flat line).

a. The font is DejaVu Sans Mono (tested with dejavu 2.23 from Ubuntu 8.04, any font version should apply). I also tried FreeSans Mono, and it exhibits the same issue at more font sizes.
b. The font size must be 12pt (96DPI). Other sizes are ok.
c. Hinting should be set to hintstyle=hintslight. Other hinting styles are ok.
d. The character that manifests the problem is U+1FB7, ᾷ

WHAT ACTUALLY HAPPENS: The perispomeni over this character (ᾷ) is shown as if it was a macron (flat horizontal line).

WHAT SHOULD HAPPEN: The perispomeni should appear properly (as it does in other sizes, similar to the tilde).

Simos Xenitellis <simos>


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    Follow 25 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    Wed 02 Nov 2016 06:21:43 AM UTC wl Carbon-CopyRemoved perhaps also a release. -email is unavailable- => -
    Wed 02 Nov 2016 06:21:27 AM UTC wl Carbon-CopyRemoved be a freetype bug rather than a dejavu bug. this is with freetype from cvs as of june 05. i believe there were some more changes since then => -
    Wed 02 Nov 2016 06:21:21 AM UTC wl Carbon-CopyRemoved then => -
    Wed 02 Nov 2016 06:21:15 AM UTC wl Carbon-CopyRemoved 15 and 16 pt/em. this may => -
    Wed 02 Nov 2016 06:21:10 AM UTC wl Carbon-CopyRemoved 11 => -
    Wed 02 Nov 2016 06:21:03 AM UTC wl Carbon-CopyRemoved it is hard to read at any size below 15 or 16. but the autofitter still ends up with more of a macron at 10 => -
    Wed 02 Nov 2016 06:20:56 AM UTC wl Carbon-CopyRemoved given the instructions => -
    Wed 02 Nov 2016 06:20:51 AM UTC wl Carbon-CopyRemoved and as expected => -
    Wed 02 Nov 2016 06:20:45 AM UTC wl Carbon-CopyRemoved 11 and 10 pt/em. without anitaliasing => -
    Wed 02 Nov 2016 06:20:38 AM UTC wl Carbon-CopyRemoved 15 => -
    Wed 02 Nov 2016 06:20:33 AM UTC wl Carbon-CopyRemoved 16 => -
    Wed 02 Nov 2016 06:20:27 AM UTC wl Carbon-CopyRemoved 19 => -
    Wed 02 Nov 2016 06:20:21 AM UTC wl Carbon-CopyRemoved 20 => -
    Wed 02 Nov 2016 06:20:17 AM UTC wl Carbon-CopyRemoved 21 => -
    Wed 02 Nov 2016 06:20:09 AM UTC wl Carbon-CopyRemoved the tilde looked like a macron at 22 => -
    Wed 02 Nov 2016 06:20:00 AM UTC wl Carbon-CopyRemoved i saw a clear tilde at all readable pt sizes. with forced autofitting => -
    Wed 02 Nov 2016 06:19:38 AM UTC wl Carbon-CopyRemoved pt size ≡ pt/em.) with the bytecode interpreter and grayscale => -
    Wed 02 Nov 2016 06:19:32 AM UTC wl Carbon-CopyRemoved at ftview's default dpi => -
    Wed 02 Nov 2016 06:19:25 AM UTC wl Carbon-CopyRemoved is shown incorrectly. it is shown as with a simos> macron (horizontal line) instead of something like a tilde. i just tried it in ftview. (aiui => -
    Wed 02 Nov 2016 06:19:17 AM UTC wl Carbon-CopyRemoved at size 12 and rendered with simos> dejavu sans mono => -
    Wed 02 Nov 2016 06:19:10 AM UTC wl Carbon-CopyRemoved ᾷ => -
    Wed 02 Nov 2016 06:18:53 AM UTC wl Carbon-CopyRemoved at size 12 (greek small alpha with perispomeni+ypogegrammeni) from: james cloos - 2008-06-10 20:36 >>>>> "simos" == simos xenitellis writes: simos> i just noticed that u+1fb7 => -
    Wed 02 Nov 2016 06:18:38 AM UTC wl Carbon-CopyRemoved re: [dejavu-fonts] u+1fb7 in dejavu sans mono => -
    Tue 18 Aug 2009 11:02:03 AM UTC pmw Carbon-Copy- => Added the tilde looked like a macron at 22
        Carbon-Copy- => Added 21

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