How does import capture obscured windows?

[Dero]

Hi,

I'm running up-to-date Ubuntu with up-to-date ImageMagick and I have noticed that the import tool is able to capture a window that is partially or completely obscured by another window. In other words - the window I'm capturing needn't to be the topmost window. My question is - how does it do that?

xwd tool is unable to produce the same effect and while looking into the import source code, I wasn't able to identify the idea behind this. I would greatly appreciate any help. Does it rely on XComposite extension somehow or is there a way to achieve such result in "bare" X?

Thank you!

[anthony]

It depends on the XServer. I am not certain what 'X:' uses but it has to get the data from the x server. I would not rely on it.

Xwd probably requests a specific section of the display root window. so it is always the top most obscure window.