Public bug reported:
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).
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.
So logging in with the dual-monitor side-by-side setup causes 3D
acceleration to be broken for that session (even when it switches to
single monitor by configuration). However going back to lightdm,
unplugging the external monitor, then log in and reconnect the external
monitor is ok.
** Affects: lightdm (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1292467
Title:
Lightdm on dual-screens can break 3D acceleration
Status in “lightdm” package in Ubuntu:
New
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).
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.
So logging in with the dual-monitor side-by-side setup causes 3D
acceleration to be broken for that session (even when it switches to
single monitor by configuration). However going back to lightdm,
unplugging the external monitor, then log in and reconnect the
external monitor is ok.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1292467/+subscriptions
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