multihead support across GNOME

[Mark McLoughlin <mark skynet ie>]

Hi Guys,
	Jonathon and myself were discussing a patch to make
gnome-settings-daemon render the background on all available screens.
Jonathon, of course, was immediately interested in what other work
would be required for multihead support in the control center. So, I
thought I'd clarify to the list what 'multihead' support is and what
work has been done already ...

	So gtk+ HEAD provides three types of multihead support:

	1) multiscreen - this is the most commonly requested feature.
	   Basically, you have more than one physical screen and when
	   you start up GNOME, you expect each screen to behave more
	   or less like a seperate workspace.

	2) xinerama - this is similar to multiscreen, except each
	   physical screen isn't like a seperate workspace but are
	   configured to behave like a single virtual screen.

	3) multidisplay - this is where a single application can be
	   running on multiple distinct X displays at once.

	So, what's been done already ? (on various branches etc.)

	* In a multiscreen configuration the panel will bring up at
	  least one panel on every screen. All launched apps and
	  dialogs etc. will come up on the same screen as the panel
	  from which you launched the app or dialog .. The tasklist
	  will only display apps running on that screen .. Nautilus
	  will draw the same background on all screens, dialogs,
	  main windows, launched apps etc. will all come up on the
	  correct screen ... Metacity will manage all screens at the
	  same time, you'll have a distinct set of workspaces on each
	  screen etc. If Nautilus isn't drawing the background, g-s-d
	  will draw the same background on each screen.

	* With Xinerama, most things will Just Work without any
	  modifications to the app. The only two exceptions I can
	  think of to this is that the panel doesn't extend across the
	  virtual screen but only extends across the physical screen -
	  so it behaves similarily to a multiscreen setup - and
	  Metacity's maximisation behaviour is different.

	* So far, absolutely zero multidisplay work has been done -
	  and that's because no-one has thought of a good use for it
	  yet. Why would you want your app running on two display's at
	  the same time? The only use I can think of is in Bonobo,
	  because a component could be running on several displays at
	  once.

	Anyway, I hope that clears up any confusion ...

Good Luck,
Mark.