GSoC : Multiscreen management

[Will Stephenson]

On Friday 02 April 2010 00:09:01 Björn Ruberg wrote:
> > I have to check the difference between "Monitor", "Screen", "Display" and
> > "Head" or are those actually the same thing ?
> 
> "Monitor", "Display" and "Head" are probably the same - in Kephal they are
> named as "Output". "Screen" ist actually something different. A screen can
> have several outputs ordered left to right. If you have two monitors with
> 1600x1200 pixels beside each other, you have a screen of 3200x1200 pixels
> and two outputs in it. One at position 0x0 and one at 1600x0.

Aike, could you shed some light on this question?  Or Aaron, if you have the 
overview of how Kephal works from mentoring Aike?

Björn's description matches the xrandr model, but not the Kephal one.  Xrandr 
1.3 has a single Screen numbered 0 but does not support additional Screens; 
xrandr Screens are distinct from the screennumber in X's $DISPLAY, and 
multiple Screen support is being discussed again for xrandr 1.4 according to 
one of our local Xorg guys.

Kephal has both multiple Outputs and multiple Screens in its model.  A screen 
owns zero or more Outputs, But it also seems that one Screen per output is 
created, looking at the usage of Kephal in KRunner, Plasma and KWin, which 
iterate, because they iterate the screens, react to screen added/removed 
signals, and use screen ids for panel and popup placement.  If this is the 
case I'm not sure why there are both Screens and Outputs.   Perhaps it's 
future-proofing for when xrandr supports multiple Screens.  But if that is 
true, I don't know why Plasma and KWin react to Screen changes but not Output 
changes.

Will