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[Rael <rael.gc@xxxxxxxxx>]

Interesting. My previous version was 12.04. And I spent a huge time
wondering why I'm facing bad performance when enabling the 3D card +
external monitor.

Wondering if every people complaining about the poor 3D accel + external
monitor get to know about this bug, the size of "affects X people" will
increase a lot.

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You received this bug notification because you are a member of Desktop
Packages, which is subscribed to unity-greeter in Ubuntu.
https://bugs.launchpad.net/bugs/1292467

Title:
  Dual screen greeter can break 3D acceleration

Status in Release Notes for Ubuntu:
  Fix Released
Status in unity-greeter package in Ubuntu:
  Triaged

Bug description:
  When booting with two screens (internal LVDS and VGA), lightdm comes
  up in a mode where it displays separate screen content on both
  displays (so no mirror mode). These screens seem to be arranged side-
  by-side regardless of the fact that (like in my case) the combined
  width can be greater than 2048 and that is not supported with 3D
  acceleration at least on that older i945GME graphics.

  This results in very poor graphics performance and compiz using a lot
  of cpu cycles (which are rather limited on this Atom N270 anyways).
  Even worse, this does not get resolved when changing the setup in
  system settings to either only having one screen active or arranging
  them on top of each other).

  WORKAROUND:
   * Plug in external monitor after login (1)
   * Boot with "video=LVDS-1:d" (2)

  (1) Booting with only the internal screen and then plugging in the
  external one after login seems to handle this better (although I
  probably need to remove any previous config to get into a kind of
  vanilla state again). Also it seems to be ok when I had the dual
  monitor boot and lightdm coming up side-by-side, when unplugging the
  external monitor before logging in.

  (2) This will completely disable the internal screen for that boot. It
  cannot be enabled through the settings dialogue.

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