Ryan,

You should definitely say "monitor" not "screen" as the latter is easily 
confused with "Screen", which as Bryce points out, often has several monitors.  
The only case where there are multiple root windows is where there are multiple 
Screens, each with its own root.  Multiple Screens is generally a less flexible 
configuration than Xinerama, except that it does allow monitors (and usually 
multiple video cards) with different colour depths and Visuals.  A multi-Screen 
configuration is basically a set of independent displays with a common keyboard 
and mouse, but supported by a single X server.  Rarely seen these days.

On a broader issue, I think you are trying to tackle too narrow a problem.  The 
resolution changing problem is a special case of a more general situation - 
something wants to take the display hardware (or some subset of it) away from 
the Window Manager, perhaps also the X server, and existing clients, without 
altering their stored state.  This is exactly what happens when you switch VTs, 
which is already well supported.  (In fact switching VTs seems a reasonable 
work-round for the full-screen-with-resolution-change problem, at least when 
VTs are available.)  The only difference I would see is that you want 
applications to take a subset of the monitors in some cases.  Looked at like 
this, asking the WM to change the resolution looks too specialised.  It should 
be OK for the application to change the resolution, so long as the WM knows to 
do nothing about it.  For this to work well, the solution involves both the WM 
and X server, but that was probably true of your original prop
 osal.

> ...  figuring out how to specify a monitor to go fullscreen ...

What is wrong with _NET_WM_FULLSCREEN_MONITORS?

Giles



-----Original Message-----
From: wm-spec-list-boun...@gnome.org [mailto:wm-spec-list-boun...@gnome.org] On 
Behalf Of Bryce Harrington
Sent: 01 November 2012 11:57 AM
To: Ryan C. Gordon
Cc: wm-spec-list@gnome.org
Subject: Re: Proposing _NET_WM_STATE_FULLSCREEN_EXCLUSIVE

On Thu, Nov 01, 2012 at 12:26:00AM -0400, Ryan C. Gordon wrote:
> Two other unrelated n00b questions from me, to make sure I'm understanding 
> the system correctly:
> 
> - Should all the places we say "screen" in this spec really say "monitor"? 
> I'm using a lot of overloaded X11 vocabulary interchangeably, and I probably 
> shouldn't.

On a multi-head RANDR system, there is a single "Screen" stretched
across the multiple displays or monitors.

> - Is there always one root window per monitor? I have text for setting a root 
> window property, and it's more useful if it can note the current fullscreen 
> window for that monitor (to cover Martin's concerns). If there's only one 
> root window that covers all monitors, I need to change this to be an array. 
> My understanding is that Xinerama stretches the root window across multiple 
> monitors, but my reading of XRandR is that this isn't true there. You can see 
> the text in question, in both forms, here:
> 
>      http://hg.icculus.org/icculus/wm-fullscreen-spec/rev/50b9d9a09539
> 
> ... the _NET_RESOLUTIONS property as it currently stands is only useful if 
> the app can effectively enumerate multiple root windows, too, or if the app 
> doesn't care what monitor it lands on.
> 

RANDR uses one screen for multiple monitors, and one root window for
that screen.  Thus one root window for all monitors.

Xinerama uses multiple screens which are stitched together.

I don't know about use cases where there are multiple root windows in an
X session, but that would be an uncommon layout at best.

Bryce
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