XGetImage returns junk with Xorg/dummy_drv/VTs

McDonald, Michael-p7438c Michael.McDonald at gdc4s.com
Mon Nov 24 09:19:49 PST 2008


> -----Original Message-----
> From: Adam Jackson [mailto:ajax at nwnk.net] 
> Sent: Monday, November 24, 2008 8:55 AM
> To: McDonald, Michael-p7438c
> Cc: xorg at lists.freedesktop.org
> Subject: Re: XGetImage returns junk with Xorg/dummy_drv/VTs
> On Fri, 2008-11-21 at 15:23 -0700, McDonald, Michael-p7438c wrote:
> > I'm trying to run the Xorg server using the dummy driver in the
> > "background" in Linux. Everything works fine as long as the 
> dummy Xorg
> > has the VT "focus". If it's in the background, then 
> XGetImage returns
> > junk data.

> Yes, it does that.  When Xorg loses the VT, it empties the 
> clip list for
> the root window.  All drawing to the root window gets thrown away, and
> all readbacks from it do nothing (which looks like 
> uninitialized data).

  Why would it do that? X apps don't know anything about VT switching,
nor should they.

> I believe some combination of -novtswitch and -sharevts should get
> around this by effectively making it so the X server doesn't have a VT
> at all, and thus can't lose it.

Using `sudo X :1 -config /etc/X11/xvfb1.config -ac -sharevts -novtswitch
&` on a RHEL5 machine with the nvidia driver and XGetImage works! Run
the same command on a RHEL5.2 machine with the intel driver and
XGetImage returns garbage. Unfortunately, I ultimately need to run using
the Intel driver in at least three invocations of Xorg.

So maybe this in an Intel driver bug? But I don't understand how the
intel driver could effect a separate process using the dummy driver,
other than some weird interaction with the VT switching stuff.

Mike McDonald

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