Bug 1374989

Summary: Qt 5 uses wrong fontconfig defaults at least for subpixel antialiasing
Product: [Fedora] Fedora Reporter: Kevin Kofler <kevin>
Component: qt5-qtbaseAssignee: Than Ngo <than>
Status: CLOSED EOL QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: low Docs Contact:
Priority: low    
Version: 24CC: jgrulich, jreznik, mike, ovasik, rdieter, than
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2017-08-08 17:16:59 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:

Description Kevin Kofler 2016-09-11 13:02:10 UTC
Description of problem:
Qt 5 appears to not enable subpixel antialiasing by default when freetype-freeworld is installed, whereas Qt 3 and 4 do. Only when I explicitly enable subpixel antialiasing in KDE System Settings, Qt 5 picks it up.

Version-Release number of selected component (if applicable):
qt5-qtbase-5.6.1-3.fc24

How reproducible:
Always? Feedback wanted…

Steps to Reproduce:
1. Install freetype-freeworld.
2. Restart your session.
3. Look at the antialiasing of various Qt applications. Use KMag to make sure you can see the effect.

Actual results:
While Qt 3 and 4 applications use subpixel antialiasing (i.e., you can see colors in KMag), Qt 5 applications do not (i.e., you see only grayscale).

Only if you explicitly enable subpixel antialiasing in KDE System Settings (rather than keeping it at the default "System default" setting) and then restart your session again (or at least the applications you are checking), you will see the wanted effect in Qt 5 applications.

Expected results:
Qt 5 applications should automatically be subpixel-antialiased if freetype-freeworld is installed, as Qt 3 and 4 applications are.

Additional info:
There is a point&click workaround (explicitly enable subpixel antialiasing in KDE System Settings), thus the low severity and priority.

Comment 1 Rex Dieter 2016-09-11 13:37:31 UTC
It may depend on the fontconfig default for subpixel rendering (I *believe* it is disabled by default).

For example, if you link/copy:
/usr/share/fontconfig/conf.avail/10-sub-pixel-bgr.conf
to
/etc/fonts/fonts.conf.d/

does that help?

Comment 2 Rex Dieter 2016-09-11 13:38:16 UTC
Or use one of:
/usr/share/fontconfig/conf.avail/10-sub-pixel-rgb.conf   /usr/share/fontconfig/conf.avail/10-sub-pixel-vrgb.conf
/usr/share/fontconfig/conf.avail/10-sub-pixel-bgr.conf  /usr/share/fontconfig/conf.avail/10-sub-pixel-vbgr.conf

depending on what you want, of course.

Comment 3 Kevin Kofler 2016-09-11 20:30:57 UTC
But why does it work out of the box in Qt 3 and 4 then? Are they the ones not honoring the system defaults?

Comment 4 Fedora End Of Life 2017-07-25 22:58:10 UTC
This message is a reminder that Fedora 24 is nearing its end of life.
Approximately 2 (two) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 24. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
of '24'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version'
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not
able to fix it before Fedora 24 is end of life. If you would still like
to see this bug fixed and are able to reproduce it against a later version
of Fedora, you are encouraged  change the 'version' to a later Fedora
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's
lifetime, sometimes those efforts are overtaken by events. Often a
more recent Fedora release includes newer upstream software that fixes
bugs or makes them obsolete.

Comment 5 Fedora End Of Life 2017-08-08 17:16:59 UTC
Fedora 24 changed to end-of-life (EOL) status on 2017-08-08. Fedora 24 is
no longer maintained, which means that it will not receive any further
security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this
bug.

Thank you for reporting this bug and we are sorry it could not be fixed.