How to tell X.org 7.1.1 the absolute position of its Screens?

[Leif Bergerhoff]

Hi all.

I'm working on a research project at university. Part of it is a 2x2 video 
wall with HD-projectors which are controlled by a linux-pc. X.org 
7.1.1 is running on it and additionally a proprietary software that manages 
things like the calibration of the projectors (the projectors are mounted in 
such a way that their pictures overlap each other - as you can see in my 
draft below).
Now my idea is to use only the X-Server (if it's possible) to do most of what 
this software does.
But therefore i still have a couple of questions:

1. How can I move a Screen, defined in xorg.conf?

  or in other words

  I want to change the absolute position of a screen (just because about 100 
pixels of the hd-projectors image get lost at the left border of the video 
wall...)

  -> I just experimented around with Modelines but I just got a 'Not supported 
by Hardware' message

2. As I said before (and I hope you can see it from my draft below), there are 
different areas of my video wall, where at least one screen overlaps another 
one. Of course the X Window System treats the 4 defined Screens as 4 
independent displays without knowing they overlap each other, so that 
information is lost in the * and # marked fields.
Is there a possibility - let's say - to tell X to send the information of the 
last 100 lines of information of Screen 1 to Screen 3, too?

3. Can I use X.org to put an alpha-mask on my displays?
   My aim is to double information as mentioned above in 2. and do something 
like soft blending.

+-------------+-----+-------------+
|             |*****|             |
|  Screen 1   |*****|   Screen 2  |
|             |*****|             |
+ - - - - - - + - - + - - - - - - +
|*************| ### |*************|
|*************| ### |*************|
+ - - - - - - + - - + - - - - - - +
|             |*****|             |
|  Screen 3   |*****|   Screen 4  |
|             |*****|             |
+-------------+-----+-------------+

* = 2 Screens overlapping
# = 4 Screens overlapping

 It would be great if someone could help me.

 Thanks,
 Leif