[ltp] Fglrx big desktop mode

[paquita]

Hello,

I am trying to configure my T42p to use the fglrx driver's big desktop 
mode. I've been playing with big desktop and clone modes over the last 
two days, and also a little with MergedFB when I failed to do what I 
wanted, but I'm stuck with some questions. I'd be grateful if somebody 
could help me with these questions, or point me to a reliable source of 
information, since what I've found up to now has rather confused me, I'm 
afraid!

My system: I'm running Ubuntu Edgy (2.6.17-10 kernel), the laptop's LCD 
has 1600x1200 resolution, and the external screen is an LG 1280x1024 LCD.

What I'm trying to do: ideally, I'd like a big non-rectangular desktop, 
with a 1600x1200 area next to a 1280x1024 one. If that cannot be done, a 
3200x1200 desktop would be ok too, provided the 1280x1024 monitor can 
display at its native resolution.

What I have now:

1. In big desktop mode, I get a 3200x1200 desktop, but the external 
monitor displays 1600x1200 pixels on a 1280x1024 area, and as a result 
of the resampling the picture is too fuzzy to be usable.

Does the virtual desktop have to be rectangular? If no, how do I tell 
xorg.conf? If yes, can I tell the external screen to display only a 
1280x1024 area, and scroll around to follow the mouse when it moves out 
of the displayed area?

2. Scrolling around does not seem to go that well either: if I select 
the 1600x1200 resolution, I get the same picture cloned on both screens 
(as expected), and the 1280x1024 monitor scrolls around to follow the 
mouse (good), but what puzzles me is that the picture on the external 
monitor is still fuzzy (I would have expected that if the 1280x1024 
monitor displays only 1280x1024 pixels out of 1600x1200, I would get the 
normal, undegraded picture). Am I missing something?

3. By contrast, if I select the 1280x1024 resolution, I have the same 
picture on both screens as expected, and the picture on the external 
monitor is of the usual, good quality.

As I'm quite new to this, maybe I'm making false assumptions here. Any 
suggestions welcome! Thanks in advance,
Paquita

######################################
Here are the modes xrandr gives me, and the relevant sections of my 
xorg.conf:

paquita@marlon:~ $ xrandr
 SZ:    Pixels          Physical       Refresh
 0   3200 x 1200   ( 805mm x 302mm )   60 
 1   1600 x 1200   ( 805mm x 302mm )   60 
*2   1280 x 1024   ( 805mm x 302mm )   75   70  *60 
 3    800 x 600    ( 805mm x 302mm )   75   72   70   60   56   47 
 4   1152 x 864    ( 805mm x 302mm )   60   75   70 
 5   1024 x 768    ( 805mm x 302mm )   60   75   72   70 
 6   1024 x 480    ( 805mm x 302mm )   60 
 7    848 x 480    ( 805mm x 302mm )   60 
 8    720 x 576    ( 805mm x 302mm )   60 
 9    720 x 480    ( 805mm x 302mm )   60 
 10   640 x 480    ( 805mm x 302mm )   75   72   60 
 11   640 x 400    ( 805mm x 302mm )   75   60 
 12   640 x 350    ( 805mm x 302mm )   60 
 13   512 x 384    ( 805mm x 302mm )   60 
 14   400 x 300    ( 805mm x 302mm )   75   60 
 15   320 x 240    ( 805mm x 302mm )   75   60 
 16   320 x 200    ( 805mm x 302mm )   75   60 
Current rotation - normal
Current reflection - none
Rotations possible - normal
Reflections possible - none

#################################
Section "Monitor"
    Identifier   "aticonfig-Monitor[0]"
    Option        "DPMS" "true"
EndSection

Section "Device"
    Identifier  "aticonfig-Device[0]"
    Driver      "fglrx"
    Option        "DesktopSetup" "horizontal,reverse"
    Option        "Mode2" "1280x1024,800x600"
    BusID       "PCI:1:0:0"
EndSection

Section "Screen"
    Identifier "aticonfig-Screen[0]"
    Device     "aticonfig-Device[0]"
    Monitor    "aticonfig-Monitor[0]"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Depth     24
        Modes    "1600x1200" "1280x1024" "800x600"
    EndSubSection
EndSection

Section "ServerLayout"
    Identifier     "Default Layout"
    Screen      0  "aticonfig-Screen[0]" 0 0
    InputDevice    "Generic Keyboard"
    InputDevice    "Configured Mouse"
    InputDevice    "Synaptics Touchpad"
EndSection

Section "DRI"
    Mode         0666
EndSection

Section "Extensions"
    Option        "Composite" "0"
EndSection
####################################