[regression] [USE_MODERN_COMPIZ_GL] Launcher overdrawn; transparency lost and white line appears.

It appears this bug and bug 1036575 only happens when no window is underneath the launcher.

If a window is under the launcher and triggering damage then it's all rendered correctly.

Further testing shows the trigger for this bug is damage to the panel (or under it).

The problem is that redrawing the panel causes the launcher to be redrawn too, even though there was no damage under the launcher.

Looks like the real issue is the new full screen buffer swapping in gles2. It's allowing plugins to render outside of the damage region (which was previously hidden).

This is probably the same root cause as bug 1026986 and bug 1022463.

Analysed the the content of wt->GetDrawList() and confirmed the cause. When just the panel is damaged, the DrawList does not contain any geometry/region for the launcher, yet somehow a launcher redraw is always triggered by panel damage.

One simple fix is:

void UnityScreen::nuxDamageCompiz()
{
  cScreen->damageScreen();
}

It's robust but arguably not ideal. If nux needs to redraw on any monitor it will trigger full screen damage (all monitors). Though nux should not need to redraw at all for most frames, so maybe it's not an issue...

Fix committed into lp:unity at revision 2586

This bug was fixed in the package unity - 6.4.0-0ubuntu1

---------------
unity (6.4.0-0ubuntu1) quantal-proposed; urgency=low

  [ Łukasz 'sil2100' Zemczak ]
  * New upstream release.
    - Software Center add to launcher icon animation is delayed when the
      launcher is in auto-hide mode (LP: #1012896)
    - Home lens: Applications show up in Music category (LP: #1040101)
    - WARN unity.hud.hud Hud.cpp:185 Attempted to close the hud connection
      without starting it (LP: #1039451)
    - Text field textures do not update when maximum width changes.
      (LP: #1037187)
    - An application is closed if manually removed from favorites on gsettings
      (LP: #1032157)
    - The switcher (Alt+Tab) is showing incorrect windows after using Deskop
      Wall (Ctrl+alt+<direction>) (LP: #1031959)
    - Dragging icons to reorder -away from launcher causes the dragged icon
      image edges to fade away(cut off) (LP: #1026247)
    - Screen flickers when changing launcher icon size. (LP: #1024113)
    - Arrow for indicating lenses points empty space on alt+F2 (LP: #998752)
    - [previews] Music album tracks do not have a scroll-bar when needed.
      (LP: #1039462)
    - [USE_MODERN_COMPIZ_GL] With unity scrollbar support enabled, hotplugging
      monitors doesn't work (LP: #1039410)
    - [previews] Track titles aren't escaped (LP: #1039020)
    - Launcher - Edge of tiles (with backlight disabled) is too opaque
      (LP: #1038138)
    - [USE_MODERN_COMPIZ_GL] Benchmark window appears behind the Unity shell
      now (LP: #1036609)
    - [GLES] [USE_MODERN_COMPIZ_GL] Unity shell (Launcher and Panel) are
      missing if framebuffer_object is disabled (LP: #1036569)
    - [USE_MODERN_COMPIZ_GL] Benchmark window is mostly invisible, shrunken
      and displaced (LP: #1036528)
    - Unity quicklist menu items leak memory (LP: #1036338)
    - Icon resized between 32 - 48 - 64 look jaggy (LP: #1036231)
    - [Regression] Hideous low-res icon when using the HUD with autohide
      enabled. (LP: #1035951)
    - [regression] Selecting an item of the BFB quicklist when the dash is
      open, causes it to hide (LP: #1035641)
    - Launcher - Switch on "backlight toggles" mode by default (LP: #1033866)
    - Unity spends 15% of time in PlacesGroup::ComputeContentSize when opening
      dash (LP: #1033306)
    - Launcher dragged icon is not redrawn when the mouse pointer is not moved
      (LP: #1032700)
    - Bottom - Up key navigation is broken in dash filterbar (LP: #1028810)
    - Launcher - SD card can not be ejected by drag-n-dropping to trash
      (LP: #960910)
    - Alt-tab - The app name in the integrated menu should not change during
      Alt-tab switching (LP: #950782)
    - Dash - If only one Category Header is displayed, it should be
      automatically expanded (LP: #950710)
    - Launcher - Unity mouse wheel scroll too small (LP: #906072)
    - boot moves desktop icons (LP: #886667)
    - Alt-tab - Reduce the spread delay for all items other than the initial
      item the select lands on after alt-tab opens (LP: #838232)
    - Launcher - Launcher should never autohide when the cursor is positioned
      over the Launcher (e.g. When ...