XGetImage returns junk with Xorg/dummy_drv/VTs

Peter Harris peter.harris at hummingbird.com
Mon Nov 24 14:02:18 PST 2008

Peter Harris wrote:
> McDonald, Michael-p7438c wrote:
>>   In the X protocol, there is no concept of the root window being
>> obscured.
> I don't see why not. If I am running multiple desktops, the root of one
> desktop may be obscured if I am viewing a different desktop.

I forgot to remind you about Xsecurity/Xace. In a properly secured
setup, any attempt to do an XGetImage on the root window will result in
BadAccess (and no image); doing a GetImage on your own bottommost
root-sized window will result in an empty image.

This isn't just theoretical; SSH -X tunnels typically set this up by
default, for example.

In this case, you might as well imagine that the root window is
obscured, at least from the perspective of your application. The
obscuring is artificial, granted, but still present. Your app isn't
allowed to see bits from other applications, so it doesn't.

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

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