Multiple Servers (Was RE: XGetImage returns junk with Xorg/dummy_drv/VTs)

Peter Harris peter.harris at
Mon Nov 24 17:06:08 PST 2008

McDonald, Michael-p7438c wrote:
>   I still feel that Xorg+dummy_drv should return a valid image but we
> can agree to disagree on that.

Actually, I agree with you on that point (and said so a few messages
back). Where we can agree to disagree is on the topic of weather
GetImage(root_window) is a useful operation in general.

>   So, my problem is I need at least three X servers running on a single
> machine. Each X server needs to support hardware accelerated OpenGL and
> XVideo-MotionCompensation. Our underlying hardware is Intel GM45 based.
> The three servers need to be completely independent of each other for
> security reasons. None of the three will have access to any real
> displays. We'll use access to the framebuffers (XGetImage would have
> been nice but we're willing to modify the driver if necessary) to
> composite the three outputs into a single, combined out.

>   Any suggestions on a better approach?

If performance matters (and if you need XvMC, I'm guessing it does), you
may be better off biting the bullet and writing a stronger set of Xace
hooks to get the security you need from a single server. You won't get
performance with GetImage.

Other than that, perhaps you can use the Composite extension to redirect
drawing into pixmaps, which (unlike windows) can be reliably retrieved
with GetImage.

xcompmgr (and/or compiz) might be an interesting base to start from.

Peter Harris
     Hummingbird Connectivity - A Division of Open Text
Peter Harris          
Research and Development        Phone: +1 905 762 6001
peter.harris at    Toll Free: 1 877 359 4866

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