Snapshot problems

[Graham Samuel]

I suppose it's just finger trouble, but I'm having great difficulty  
using import snapshot and export snapshot - the RunRev docs seem not  
to be completely specific on this. For example, while apparently I can  
take a snapshot of something that isn't open and isn't visible (the  
docs say so!), I don't seem to be able to take a snapshot of an object  
whose loc is outside the visible area. For example I have an image  
which I've placed out of site at 2000,2000 based on a quite small  
stack, say 800 by 600 pixels. I'm used to this technique for hiding  
stuff from the user, and also for working with objects larger than the  
visible area - in this case, I am doing both of these. Now I want to  
tinker with the image. The statement

import snapshot from rect 1375,2592,1749,2625 of this stack

compiles OK but results in an execution error. Experiments seem to  
show that a statement of the same form restricted to the bounds of the  
stack's window work OK.

What I'm actually trying to do is to create a composite image at  
screen resolution, by overlaying images on top of one another and then  
taking a snapshot of the resultant screen area, but all without the  
user seeing anything. My experiments appear to show that I can do it  
while the various objects are visible (in the visible area) but not  
otherwise. Can anyone explain how this could be done?

TIA

Graham