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[gouri <stephane.gourichon_lpad@xxxxxxx>]

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https://bugs.launchpad.net/bugs/1547077

Title:
  Some glyphs drawn consistently wrong, bug comes and go

Status in xorg package in Ubuntu:
  New

Bug description:
  # 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)

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