Public bug reported:
# Summary
* Some glyphs badly drawn at some moments.
* When happens, same glyph drawn on various windows shows same corruption.
* Problem comes and go.
# Context
Laptop, using Intel driver.
Expected: all glyphs rendered correctly.
Observed: some glyphs not rendered correctly
* sometimes (problem comes and go, severity varies)
* *some* glyphs are affected. For example, letter 'a' of a certain size will be
replaced by colored garbage at many places where it appears (see
2016y02m18d_16h05m35s_0100Z_same_corruption_on_different_windows.png ), but
other 'a' with different size, italic, bold, etc will be unaffected
* in some applications (e.g. xfce whisker menu), some glyphs are rendered
correctly or not depending on the direction of mouse hovering. See video
2016y02m16d_21h41m14s_0100Z_whisker_menu_missing_glyphs.mp4 .
* in menu of gtk application, some glyphs are "fixed" by opening the menu, but
not all. For example, in xfce4-terminal, letter A of "Affichage" and its menu
content as well as "Aide" is affected. Opening "Affichage" menu does not fix
anything. Opening "Aide" menu fixes the "A" of "Aide". Changing window size
reactivates the bug on "A" or "Aide". See video
2016y02m18d_16h14m25s_0100Z_glyph-redrawn-bug.mp4 .
* text under icons on desktop is affected, but shadows are not. See
2016y02m16d_21h32m11s_0100Z_x_bug_reenabling_antialias_reactivates_problem_shadow_unaffected.png
# Affected applications
Affected applications include:
* xfce whisker menu,
* xfce4-terminal,
* firefox (see 2016y02m17d_18h08m27s_0100Z_x_bug_glyph_firefox_gnome_org.png
2016y02m16d_21h32m11s_0100Z_x_bug_reenabling_antialias_reactivates_problem_shadow_unaffected.png
),
* thunderbird (see
2016y02m16d_21h28m35s_0100Z_x_bug_affects_thunderbird_terminal.png ),
* emacs (see
2016y02m10d_18h41m49s_0100Z_wow_screen_flickers_and_most_glyphs_wrong_00.png
and subsequent ),
* superswitcher ( a gtk/gdk app)
* *NOT* affected: xterm, xmessage. Perhaps only gtk/gdk/pango/cairo are
affected.
# Additional information
This looks like a cache corruption somewhere.
On IRC #ubuntu+1, someone suggested a bug in Intel driver.
Running `xfce4-appearance-settings` and there changing any of:
* antialiasing enable/disable,
* hinting strength,
* subpixel alignment
* or dpi
immediately cures the bug (see
2016y02m16d_21h31m52s_0100Z_x_bug_disabling_antialias_immediately_cures_problem.png
)
Setting back the exact same parameters immediately reactivates the bug
(see
2016y02m16d_21h32m11s_0100Z_x_bug_reenabling_antialias_reactivates_problem_shadow_unaffected.png).
It is believed that keeping any new settings for a while will have the
bug reoccur.
It is not like bug 1536751. That one affects rendering quality of *all* glyphs,
at all times, depending on dpi. This is not the case here: *some* glyphs
(randomly chosen) are drawn corrupted (replaced by garbage or absent), not
always.
# Other
1) The release of Ubuntu you are using, via 'lsb_release -rd' or System
-> About Ubuntu
export LC_ALL=C ; lsb_release -rd
Description: Ubuntu Xenial Xerus (development branch)
Release: 16.04
2) The version of the package you are using, via 'apt-cache policy
pkgname' or by checking in Software Center
apt-cache policy xorg
xorg:
Installed: 1:7.7+13ubuntu1
Candidate: 1:7.7+13ubuntu1
Version table:
*** 1:7.7+13ubuntu1 500
500 http://fr.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
100 /var/lib/dpkg/status
3) What you expected to happen
4) What happened instead
Written above.
ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xorg 1:7.7+13ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-4.19-generic 4.4.1
Uname: Linux 4.4.0-4-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: XFCE
Date: Thu Feb 18 16:03:55 2016
InstallationDate: Installed on 2016-02-03 (14 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160203)
SourcePackage: xorg
Symptom: display
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: xorg (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug corruption xenial
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https://bugs.launchpad.net/bugs/1547077
Title:
Some glyphs drawn consistently wrong, bug comes and go
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