Debian Bug report logs - #798805
fonts-cantarell: Switch to autohinting to work around blurry rendering with CFF

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Message #3 received at submit@bugs.debian.org (full text, mbox, reply):

From: Josh Triplett <josh@joshtriplett.org>

To: Debian Bug Tracking System <submit@bugs.debian.org>

Subject: libfreetype6 2.6-1 makes Cantarell blurry (CFF?)

Date: Sat, 12 Sep 2015 21:24:00 -0700

Package: libfreetype6
Version: 2.6-1
Severity: important

[Severity important because this breaks GNOME's primary interface font.]

After upgrading to libfreetype 2.6-1, the Cantarell font shows up as
blurry; lines get smeared across pixels.  This doesn't happen with every
font; for instance, DejaVu Sans seems fine.

I've attached a pair of screenshots to demonstrate.
cantarell-blurry.png shows the blurry rendering of Cantarell; zoom in on
a vertical line such as in the 'n', 't', 'r', or 'f' of "Interface", and
notice that the vertical line gets smeared out across multiple pixels.
sans.png shows the rendering of DejaVu Sans; notice that the same
vertical lines snap to pixel boundaries.

Given that 2.6-1 re-enabled CFF, that seems like a likely culprit,
unless other significant changes occurred in the same version.

Also, given that this has happened multiple times in the past, I wonder
if a "font unit test" would help?  Take a couple of key fonts, such as
the aforementioned DejaVu Sans and Cantarell, render specific letters
with the default parameters, and scan across the resulting image at a
given y to make sure the rendering doesn't smear across pixels.  Such a
test would make sure future changes to libfreetype6 don't re-introduce
critical font rendering errors.

- Josh Triplett

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 4.1.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages libfreetype6 depends on:
ii  libc6       2.19-19
ii  libpng12-0  1.2.50-2+b2
ii  zlib1g      1:1.2.8.dfsg-2+b1

libfreetype6 recommends no packages.

libfreetype6 suggests no packages.

-- no debconf information

Message #8 received at 798805@bugs.debian.org (full text, mbox, reply):

From: Josh Triplett <josh@joshtriplett.org>

To: 798805@bugs.debian.org

Subject: libfreetype6 2.6-1 makes Cantarell blurry (CFF?)

Date: Sat, 12 Sep 2015 21:35:16 -0700

[Message part 1 (text/plain, inline)]

Would help if I actually attached the screenshots.

- Josh Triplett

[cantarell-blurry.png (image/png, attachment)]

[sans.png (image/png, attachment)]

Message #13 received at 798805@bugs.debian.org (full text, mbox, reply):

From: josh@joshtriplett.org

To: 798805@bugs.debian.org

Subject: Status of this bug?

Date: Thu, 17 Sep 2015 09:48:57 -0700

Any feedback on this bug?  This issue makes GNOME's UI painfully blurry,
and the version with this issue just migrated to testing today, exposing
many more people to this issue.

- Josh Triplett

Message #18 received at 798805@bugs.debian.org (full text, mbox, reply):

From: Steve Langasek <vorlon@debian.org>

To: josh@joshtriplett.org, 798805@bugs.debian.org

Subject: Re: Bug#798805: Status of this bug?

Date: Thu, 17 Sep 2015 16:25:30 -0700

[Message part 1 (text/plain, inline)]

On Sat, Sep 12, 2015 at 09:35:16PM -0700, Josh Triplett wrote:
> Would help if I actually attached the screenshots.

Could you please provide for comparison a screenshot using the Cantarell
font when using the older version of freetype (with CFF disabled)?

I can certainly see the differences between the two screenshots, but what I
see when looking at the Sans screenshot is the shaping is horrible - with
the F and T in the headers very crisp but horribly shaped, and the shaping
on "Window Titles" so bad that the dot of the i sits *above* the cross of
the T.  So I would have a hard time arguing that this behavior is more
correct than the behavior shown with Cantarell, which has definitely traded
off crispness for correctness of shape, and I would like to directly compare
before/after of the change in freetype.

Sorry to ask you for this, but I don't run a GNOME desktop, so this seems
the quickest way to get the information needed to move this bug forward.  I
could try running GNOME in a VM but I'm concerned that being in a VM rather
than with a real LCD monitor might prevent accurately reproducing the
behavior you're seeing, and setting up to run GNOME on real hardware would
take me a bit more effort.  I have tried to compare the before/after
behavior of freetype with the Cantarell font on a unity desktop, and despite
the fact that unity and gnome should both be working against the same
fontconfig settings, I'm not able to discern any difference in the
appearance between the old and new freetype when configuring the Cantarell
on unity: neither shows the "snap to grid" behavior of font stems that you
appear to be requesting.


The other things I notice here:

 - Your screenshots show an antialiasing setting of "grayscale".  A
   zoomed-in view of both screenshots shows that this setting is being
   respected.  In your previous screenshots for bug #730742, it appears that
   subpixel antialiasing was in play.  Is this because you had different
   fontconfig settings selected at that time, or is it because the earlier
   freetype was not correctly respecting the "grayscale" setting?

 - You have a hinting setting of "medium".  How does the appearance of this
   font vary for you with different values of hinting?  Is there no other
   value for the hinting setting that gives the crispness you're looking
   for, or is there some other reason that these other hinting settings are
   unsatisfactory for you?


The Adobe CFF behavior I'm seeing (both in your new screenshots and in my
local testing) suits *my* personal tastes just fine.  Unless you can point
to a specific way in which freetype is buggy when using the Adobe CFF engine
and either misinterpreting a font or failing to respect fontconfig
preferences, I can't see disabling Adobe CFF again in Debian.

In the original bug, there was a comment indicating that a new version of
fontconfig would be released soon that included a configuration setting for
handling different hint styles for CFF fonts vs. others:

  https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=88;bug=730742

That was in 2013, however, and we still have fontconfig 2.11.0 in Debian. 
Time for an upgrade?

There were also the comments on the upstream list that the Cantarell font
itself showed buggy hints:

  http://lists.nongnu.org/archive/html/freetype/2014-01/msg00011.html

There is a new upstream version of Cantarell in Debian since that mail was
written (0.0.16-1, uploaded Sep 2014).  I had assumed that this release
specifically addressed these bugs in the font hints.  Was this not the case?

Particularly as we have other users specifically requesting the CFF engine
(bug #795653) because it substantially improves the display of other fonts,
I don't think we should keep this functionality disabled in freetype
indefinitely to accommodate a buggy font, even if this font is a default for
GNOME.  If no one is going to take care of the bugs on this font, maybe it's
not a good choice of default.

There's also a bug report about cantarell in Fedora, including a fontconfig
setting that would avoid the use of CFF specifically for this font until the
bug can be fixed:

  https://bugzilla.redhat.com/show_bug.cgi?id=1062903


On Thu, Sep 17, 2015 at 09:48:57AM -0700, josh@joshtriplett.org wrote:
> Any feedback on this bug?  This issue makes GNOME's UI painfully blurry,
> and the version with this issue just migrated to testing today, exposing
> many more people to this issue.

Of course, if you considered this bug severe enough to warrant keeping the
package out of testing, the correct thing to have done was to file the bug
at severity: serious.

At the moment, my inclination is to reassign this bug to the fonts-cantarell
package.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek@ubuntu.com                                     vorlon@debian.org

[signature.asc (application/pgp-signature, inline)]

Message #23 received at 798805@bugs.debian.org (full text, mbox, reply):

From: Josh Triplett <josh@joshtriplett.org>

To: Steve Langasek <vorlon@debian.org>

Cc: 798805@bugs.debian.org

Subject: Re: Bug#798805: Status of this bug?

Date: Fri, 18 Sep 2015 00:07:12 -0700

[Message part 1 (text/plain, inline)]

reassign 798805 fonts-cantarell
clone 798805 -1
retitle 798805 fonts-cantarell: Switch to autohinting to work around blurry rendering with CFF
severity 798805 grave
tags 798805 + patch # Include fontconfig <match> below in 31-cantarell.conf
retitle -1 fonts-cantarell: Hints do not accurately identify font stems
tags -1 + upstream
thanks

On Thu, Sep 17, 2015 at 04:25:30PM -0700, Steve Langasek wrote:
> On Sat, Sep 12, 2015 at 09:35:16PM -0700, Josh Triplett wrote:
> > Would help if I actually attached the screenshots.
> 
> Could you please provide for comparison a screenshot using the Cantarell
> font when using the older version of freetype (with CFF disabled)?

Attached.  Notice the rendering behavior on the vertical lines in
"Interface".  With the new version, each vertical line gets smeared
across three pixels, two very faint gray and one solid black.  With the
older version, each vertical line renders as a very dark line and a
solid black line, which does not produce the headache-inducing blurry
effect.

You can see a similar effect in the rendering of other characters, such
as the curve of the 'e'.  Notice how the rendering with 2.6-1 has far
more light-grey pixels on the edges, while the previous version had a
well-defined edge stopping with a dark pixel.

Certainly Cantarell could have better hinting than it does, but the new
version of libfreetype6 has definitely regressed in the quality of its
rendering of Cantarell.

Now, that said, with some further investigation at other sizes, I
noticed something interesting.  With the new version, Cantarell renders
blurry at all sizes (or all those I tried, anyway).  However, even with
the old version, a few sizes of Cantarell render with a similar
blurriness.  The new version still seems worse, but there certainly
seems room to blame Cantarell as well.

> I can certainly see the differences between the two screenshots, but what I
> see when looking at the Sans screenshot is the shaping is horrible - with
> the F and T in the headers very crisp but horribly shaped, and the shaping
> on "Window Titles" so bad that the dot of the i sits *above* the cross of
> the T.  So I would have a hard time arguing that this behavior is more
> correct than the behavior shown with Cantarell, which has definitely traded
> off crispness for correctness of shape, and I would like to directly compare
> before/after of the change in freetype.

That sounds like the standard difference between Windows-style font
rendering and Apple-style font rendering.  Apple-style ignores pixels
and considers font shape sacrosanct, so it gives better font shape at
the expensive of blurriness.  Windows-style acknowledges the limits of
DPI and snaps to pixels, giving crisper fonts at the expense of font
shape.  Hints allow the renderer to implement such snapping to pixels,
while in the absence of good hints (or autohints), rendering has nothing
to go on but the font shape, and thus ends up with Apple-style rendering.

So if you find the new, blurry rendering more to your personal tastes,
you might prefer Apple-style rendering in general, favoring font shape
over cripsness.

> The other things I notice here:
> 
>  - Your screenshots show an antialiasing setting of "grayscale".  A
>    zoomed-in view of both screenshots shows that this setting is being
>    respected.  In your previous screenshots for bug #730742, it appears that
>    subpixel antialiasing was in play.  Is this because you had different
>    fontconfig settings selected at that time, or is it because the earlier
>    freetype was not correctly respecting the "grayscale" setting?

The former.

>  - You have a hinting setting of "medium".  How does the appearance of this
>    font vary for you with different values of hinting?  Is there no other
>    value for the hinting setting that gives the crispness you're looking
>    for, or is there some other reason that these other hinting settings are
>    unsatisfactory for you?

As far as I can tell, Cantarell looks *identical* with all values of
hinting; in all cases it looks identically blurry.

> The Adobe CFF behavior I'm seeing (both in your new screenshots and in my
> local testing) suits *my* personal tastes just fine.  Unless you can point
> to a specific way in which freetype is buggy when using the Adobe CFF engine
> and either misinterpreting a font or failing to respect fontconfig
> preferences, I can't see disabling Adobe CFF again in Debian.
> 
> In the original bug, there was a comment indicating that a new version of
> fontconfig would be released soon that included a configuration setting for
> handling different hint styles for CFF fonts vs. others:
> 
>   https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=88;bug=730742

That change doesn't actually solve the problem, though.  Note my
subsequent comments, first suggesting that that fontconfig snippet
seemed to fix the problem, but then noting that "some things still
render differently", such as tab labels.  And guess what font tab labels
render in? :)

So, that fontconfig snippet doesn't actually fix the rendering of
Cantarell.

> There were also the comments on the upstream list that the Cantarell font
> itself showed buggy hints:
> 
>   http://lists.nongnu.org/archive/html/freetype/2014-01/msg00011.html

That would certainly explain a great deal.  If Cantarell's hints don't
actually accurately reflect the "important stems", that sounds like a
bug in Cantarell, which could then make Cantarell more sensitive to the
details of font rendering.

> There is a new upstream version of Cantarell in Debian since that mail was
> written (0.0.16-1, uploaded Sep 2014).  I had assumed that this release
> specifically addressed these bugs in the font hints.  Was this not the case?

A quick check upstream confirms that the hints did not change in 0.0.16.
Nor have the hints for Cantarell Regular changed after 0.0.16, either.

> Particularly as we have other users specifically requesting the CFF engine
> (bug #795653) because it substantially improves the display of other fonts,
> I don't think we should keep this functionality disabled in freetype
> indefinitely to accommodate a buggy font, even if this font is a default for
> GNOME.  If no one is going to take care of the bugs on this font, maybe it's
> not a good choice of default.
> 
> There's also a bug report about cantarell in Fedora, including a fontconfig
> setting that would avoid the use of CFF specifically for this font until the
> bug can be fixed:
> 
>   https://bugzilla.redhat.com/show_bug.cgi?id=1062903

That setting actually switches to the autohinter rather than the font's
own hints.  Which does indeed seem to work around the problem.  With
that setting, libfreetype6 2.6-1 renders Cantarell crisply again.

That seems like an appropriate workaround to put in place.  Copying it
here for the record:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE fontconfig SYSTEM "../fonts.dtd">
<fontconfig>
  <match target="font">
    <test name="family">
      <string>Cantarell</string>
    </test>
    <edit name="autohint" mode="assign">
      <bool>true</bool>
    </edit>
  </match>
</fontconfig>

(The match section could go in the existing 31-cantarell.conf in
fonts-cantarell.)

This doesn't seem like the right permanent fix, as a look at the
upstream Cantarell repository turns up mentions that the autohinter
doesn't always do a good job either, but nonetheless it produces much
better results than 2.6-1's default rendering.  So, until the hints get
fixed, this workaround works.

> On Thu, Sep 17, 2015 at 09:48:57AM -0700, josh@joshtriplett.org wrote:
> > Any feedback on this bug?  This issue makes GNOME's UI painfully blurry,
> > and the version with this issue just migrated to testing today, exposing
> > many more people to this issue.
> 
> Of course, if you considered this bug severe enough to warrant keeping the
> package out of testing, the correct thing to have done was to file the bug
> at severity: serious.

I didn't feel I could justify more than "a bug which has a major effect
on the usability of a package, without rendering it completely unusable
to everyone."  The package certainly isn't "unusable to everyone", not
least of which because only Cantarell seems affected, and not everyone
uses that font, though many Debian users do.

> At the moment, my inclination is to reassign this bug to the fonts-cantarell
> package.

With the control commands at the top of this mail, I've generated two
such bugs against fonts-cantarell: one about its hints, and one to
include the above fontconfig snippet.

- Josh Triplett

[libfreetype6-2.5.2-4-cantarell.png (image/png, attachment)]

Message #40 received at 798805-close@bugs.debian.org (full text, mbox, reply):

From: Fabian Greffrath <fabian@debian.org>

To: 798805-close@bugs.debian.org

Subject: Bug#798805: fixed in fonts-cantarell 0.0.16-2

Date: Mon, 21 Sep 2015 07:19:02 +0000

Source: fonts-cantarell
Source-Version: 0.0.16-2

We believe that the bug you reported is fixed in the latest version of
fonts-cantarell, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 798805@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Fabian Greffrath <fabian@debian.org> (supplier of updated fonts-cantarell package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)


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Hash: SHA256

Format: 1.8
Date: Mon, 21 Sep 2015 08:31:44 +0200
Source: fonts-cantarell
Binary: fonts-cantarell
Architecture: source all
Version: 0.0.16-2
Distribution: unstable
Urgency: high
Maintainer: Debian Fonts Task Force <pkg-fonts-devel@lists.alioth.debian.org>
Changed-By: Fabian Greffrath <fabian@debian.org>
Description:
 fonts-cantarell - sans serif font family designed for on-screen readability
Closes: 798805
Changes:
 fonts-cantarell (0.0.16-2) unstable; urgency=high
 .
   * Reportedly, Cantarell looks blurry when rendered with the CFF
     engine enabled in freetype 2.6-1. As a work-around, force
     auto-hinting in the fontconfig snippet (Closes: #798805).
 .
   * Clarify copyright of files in debian/*.
   * Run "wrap-and-sort -asb".
   * Update Uploaders field to my <fabian@debian.org> account.
   * Bump debhelper compat to 9.
   * Bump Standards-Version to 3.9.6.
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Message #43 received at 798805@bugs.debian.org (full text, mbox, reply):

From: pkg-fonts-devel@lists.alioth.debian.org

To: 798805@bugs.debian.org, 798805-submitter@bugs.debian.org

Subject: Pending fixes for bugs in the fonts-cantarell package

Date: Mon, 21 Sep 2015 07:56:25 +0000

tag 798805 + pending
thanks

Some bugs in the fonts-cantarell package are closed in revision
58e5678120d7d2439544688184fb3345351c109f in branch 'master' by Fabian
Greffrath

The full diff can be seen at
http://anonscm.debian.org/gitweb/?p=pkg-fonts/fonts-cantarell.git;a=commitdiff;h=58e5678

Commit message:

    Reportedly, Cantarell looks blurry when rendered with the CFF
    
    engine enabled in freetype 2.6-1. As a work-around, force
    auto-hinting in the fontconfig snippet (Closes: #798805)

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To: 798805@bugs.debian.org

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