xinerama and struts

[Havoc Pennington <hp redhat com>]

Hi,

We probably shouldn't put this in 1.2, as I haven't tried implementing
it yet, but I just configured a xinerama setup and am feeling the 
_NET_WM_STRUT-not-working pain. (What does KWin do here?)

First the user-visible behavior I'm after: gnome panel can be on any
of the four sides of any xinerama screen. So if I have two xinerama
screens side by side, the panels are allowed to be on either side of
the dividing line between the monitors. There are 8 total panel
positions.

Window manager panel handling in various cases:
 - when maximizing, it should be to one monitor, avoiding the 4 panels 
   on that monitor
 - desktop icons should avoid all panels, but for the panels 
   in between the two monitors, struts aren't really sufficient;
   icons should be allowed on both monitors, but not underneath 
   the panels in the center.
 - for placing windows, you don't want to place overlapping any 
   panels

Here is a proposed solution that probably allows all of the above:

 _NET_WM_STRUT_XINERAMA

 Like _NET_WM_STRUT but has a 5th integer in the array, for the index
 of the Xinerama monitor the strut applies to. The strut only applies
 to that Xinerama monitor. The strut should be taken with respect to
 the geometry of the Xinerama monitor.

However, gnome-panel would probably use _NET_WM_STRUT_XINERAMA
exclusively, and never _NET_WM_STRUT. And anything you can do 
with _NET_WM_STRUT can be done with _NET_WM_STRUT_XINERAMA.

Perhaps we should just say that _NET_WM_STRUT has an optional 5th
field, and if present it confines that strut to a single Xinerama and
makes it relative to the given Xinerama. Would this count as an
incompatible change?

Havoc