[Bug 679030] New: [freetype] uneven rendering quality when bytecode is enabled

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Summary: [freetype] uneven rendering quality when bytecode is enabled

https://bugzilla.redhat.com/show_bug.cgi?id=679030

           Summary: [freetype] uneven rendering quality when bytecode is
                    enabled
           Product: Fedora
           Version: 15
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: unspecified
          Priority: unspecified
         Component: freetype
        AssignedTo: mkasik(a)redhat.com
        ReportedBy: jfrieben(a)hotmail.com
         QAContact: extras-qa(a)fedoraproject.org
                CC: behdad(a)fedoraproject.org, kevin(a)tigcc.ticalc.org,
                    fonts-bugs(a)lists.fedoraproject.org, mkasik(a)redhat.com
    Classification: Fedora


Description of problem:
After updating to the latest FreeType build for which the bytecode interpreter
has been enabled, fonts are rendered with uneven quality. The system font used
e.g. for button labels is very thin now and certain popular web fonts (e.g.
Verdana) are rendered surprisingly poorly.
Look at the four attached screenshots which demonstrate the various
combinations for which the bytecode interpreter is enabled (disabled) and
webcore fonts are installed (removed).

Version-Release number of selected component (if applicable):
freetype-2.4.4-3.fc15

How reproducible:
Always.

Steps to Reproduce:
1. Launch firefox.
2. Open http://www.bbc.co.uk .

Actual results:
Partially poor rendering depending on whether the bytecode interpreter is
enabled or not.

Expected results:
Acceptable rendering quality throughout all font families.

Additional info:
Reverting to freetype-2.4.4-2.fc15 restores globally good font rendering.

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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https://bugzilla.redhat.com/show_bug.cgi?id=679030

--- Comment #1 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-21 05:54:48 EST
---
Created attachment 479866
  --> https://bugzilla.redhat.com/attachment.cgi?id=479866
Screenshot of http://www.bbc.co.uk with system fonts and bytecode interpreter

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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https://bugzilla.redhat.com/show_bug.cgi?id=679030

--- Comment #2 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-21 05:55:38 EST
---
Created attachment 479869
  --> https://bugzilla.redhat.com/attachment.cgi?id=479869
Screenshot of http://www.bbc.co.uk with web core fonts and bytecode interpreter

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #3 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-21 05:56:31 EST
---
Created attachment 479870
  --> https://bugzilla.redhat.com/attachment.cgi?id=479870
creenshot of http://www.bbc.co.uk with system fonts and -no- bytecode
interpreter

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #4 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-21 05:57:16 EST
---
Created attachment 479871
  --> https://bugzilla.redhat.com/attachment.cgi?id=479871
Screenshot of http://www.bbc.co.uk with web core fonts and -no- bytecode
interpreter

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #5 from Kevin Kofler <kevin(a)tigcc.ticalc.org&gt; 2011-02-21 09:29:37 EST
---
Hmmm, are you sure you aren't mixing up the system fonts vs. web core fonts
screenshots?

So we have 2 separate issues there:

* re DejaVu, I know that the font looks very different with and without the
hinting bytecode. As a long-time maintainer of freetype-freeworld, I'm well
aware of this problem. The thing is, some people, and that includes the
upstream developers of DejaVu, actually LIKE the rendering with the bytecode,
and in fact DejaVu upstream recommends enabling the BCI for their fonts. I used
to disable the BCI for the DejaVu family in my freetype-freeworld packaging
because of complaints such as yours, but then I got complaints about it being
disabled (see e.g. https://bugzilla.rpmfusion.org/show_bug.cgi?id=198). Then I
reenabled it and got at least one complaint about it being enabled. You just
cannot please everyone… It is possible for you as a user to disable the BCI for
DejaVu using a config file like this:
http://cvs.rpmfusion.org/viewvc/rpms/freetype-freeworld/F-12/99-DejaVu-au...
There have been complaints to DejaVu upstream about the discrepancy, but they
say this is all by design.

* re Verdana, I think we need to figure out whether the rendering is as
intended by the font designers (as in Deja Vu's case) or whether there's a bug.
(It might be that "freetype uses hinting bytecode even at sizes so small that
the font wants to be rendered without antialiasing" issue which is already
reported somewhere.) It can be worked around with a per-font policy using a
config file similar to the above, but really, we want the BCI fixed instead.

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #6 from Kevin Kofler <kevin(a)tigcc.ticalc.org&gt; 2011-02-21 09:39:09 EST
---
I guess that, if the Verdana issue is really a size issue (unfortunately, I
can't find the report for that issue anymore), a possible solution would be to
check the font's tables for the minimum supported antialiasing size (which is
normally the minimum size the hinting bytecode was tested with), and if the
requested size is smaller than that, force autohinting (similar to how the
auto-autohint patch handles fonts with no bytecode at all). On the other hand,
that may be overly conservative.

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #7 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-21 11:15:23 EST
---
(In reply to comment #5)
No, the screenshots are labeled correctly. In attachment 479866 and in
attachment 479870, the text body is rendered using a rather ugly font, some
DejaVu variant, I guess.
Note the (Fedora) font used in the address bar which is very slim when the
bytecode interpreter is enabled. Unfortunately, the new user interface does not
allow in a straightforward manner to change hinting between "slight" and
"medium" which could be used to improve the rendering.
Freetype rendering of web core and Luxi fonts is sort of an eternal story as
underlined by bug 198082 which I reported back in 2006.

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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Ben Laenen <bl.bugs(a)gmail.com&gt; changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bl.bugs(a)gmail.com

--- Comment #8 from Ben Laenen <bl.bugs(a)gmail.com&gt; 2011-02-22 07:17:48 EST ---
I don't think that first screenshot really shows the body text with the
bytecode interpreter enabled. It's rendered exactly the same as the third
screenshot.


Anyway, there are many different ways to handle hinting, and if people claim
about bad rendering of Verdana with BCI enabled, it's because Verdana was
hinted without anti-aliasing in mind. With anti-aliasing some artifacts are
shown, especially in the diagonals which can sometimes even become almost
invisible. In DejaVu we have hinting designed for anti-aliasing (DejaVu will in
its turn be rendered worse if you disable anti-aliasing).

Next, there's also a minimum font size (defined in the tables in the font
itself) that says below which no more hinting should be applied at all (this is
usually a number like 8 or 9 ppem).


The reason why we from DejaVu recommend the bytecode interpreter is because we
can actually control that. We get a large amount of bugs reported which are
caused by the autohinter, and each time we have to say "sorry, there's nothing
we can do to fix this" (it's actually the first thing I look at if bad
rendering is reported: does this user use the autohinter?). And an autohinter
will always be worse than BCI hinting because the autohinter is unable to keep
everything consistent, and I'd say consistency is a feature you really want to
have in a font...

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #9 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-22 08:17:21 EST
---
(In reply to comment #8)
>  I don't think that first screenshot really shows the body text
> with the
>  bytecode interpreter enabled. It's rendered exactly the same as the third
>  screenshot. 
Maybe you have a second look and convince yourself first that there exist 2 x 2
= 4 combinations (with and w/o BCI; with and w/o web core fonts) which
correspond to the 4 (different (!)) attached screenshots. If you wonder that
the text body of screenshots 1 and 3 look the same then you should also look at
the URL bar which undeniably shows a clear difference in the way the default
sans serif text is rendered. I can hardly imagine that while BCI is used for
rendering GTK widgets it is not by Xulrunner. As a matter of fact, button
labels in case 3 without active bytecode interpreter looks clearly better (in
my opinion). Case 1 reminds me of older Ubuntu releases which always suffered
from too skinny characters.

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #10 from Ben Laenen <bl.bugs(a)gmail.com&gt; 2011-02-22 14:14:07 EST ---
(In reply to comment #9)
>  Maybe you have a second look and convince yourself first that there
> exist 2 x 2
>  = 4 combinations (with and w/o BCI; with and w/o web core fonts) which
>  correspond to the 4 (different (!)) attached screenshots. 
I didn't argue that. I just said that the body text in #1 clearly does not show
a font which is using the BCI, for whatever reason that may be. I'm just
clearing this out since it's 90% of the screenshot.

>  If you wonder that
>  the text body of screenshots 1 and 3 look the same then you should also look at
>  the URL bar which undeniably shows a clear difference in the way the default
>  sans serif text is rendered. 
I also did not argue that.

>  I can hardly imagine that while BCI is used for
>  rendering GTK widgets it is not by Xulrunner. 
It's much harder to imagine that the autohinter would come up with exactly the
same rendering for a font as when it's using the BCI.

My guess is that with all the fallback rules the font chosen to render the body
is FreeSans, which has no hinting instructions at all, so freetype falls back
to autohinting in screenshot 1.

>  As a matter of fact, button
>  labels in case 3 without active bytecode interpreter looks clearly better (in
>  my opinion). Case 1 reminds me of older Ubuntu releases which always suffered
>  from too skinny characters. 
Well, the keyword in that is "in my opinion". Let me tell you that the GUI font
in #1 (DejaVu) is how font developers designed it to look like. None of the
screenshots is showing how Verdana was designed to look like.

How you want your fonts to look on your screen is totally up to you to decide
(I cannot stand bitmapped fonts so I chose to have Verdana anti-aliased
myself). I'm only giving the facts here about what the rendering should look
like if you want it like the font designers designed it.

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #11 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-23 05:07:48 EST
---
Created attachment 480400
  --> https://bugzilla.redhat.com/attachment.cgi?id=480400
Screenshot of http://www.bbc.co.uk rendered by IE8 (Windows XP)

(In reply to comment #10)
>  None of the screenshots is showing how Verdana was designed to look
> like. 
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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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--- Comment #12 from Joachim Namislow <jfrieben(a)hotmail.com&gt; 2011-02-24 03:25:21 EST
---
Created attachment 480684
  --> https://bugzilla.redhat.com/attachment.cgi?id=480684
Screenshot of liberation font with bytecode interpreter

Part of a web page rendered by firefox. No fonts other than the system default
fonts have been installed. Note that the character "u" differs significantly
from the other ones. The font seems to belong to the "Liberation" font family.

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--- Comment #13 from Kevin Kofler <kevin(a)tigcc.ticalc.org&gt; 2011-02-24 10:10:13 EST
---
This one looks like a font bug, it should probably be filed against
liberation-fonts.

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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Fedora End Of Life <endoflife(a)fedoraproject.org&gt; changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |CLOSED
         Resolution|---                         |WONTFIX
        Last Closed|                            |2012-08-07 13:23:12

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[Bug 679030] [freetype] uneven rendering quality when bytecode is enabled

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