Separate X Screens - possible on Intel Integrated HD Graphics?

[Simon McVittie]

On 17/01/16 16:49, Ken Taylor wrote:
> On 01/17/2016 10:05 AM, rhkramer at gmail.com wrote:
>> On Sunday, January 17, 2016 08:10:38 AM [Michal] wrote:
>>> The usual pattern is that people ask about multiple screens but do not
>>> really want them. Having multiple screens only limits what you can do
>>> and gives you no meaningful benefits.
>>
>> On some of the industrial (process control) systems I've been
>> responsible for,
>> we put up to 4 monitors (with different displays) driven by one
>> computer in
>> front of a single operator.

Multiple heads/outputs/monitors do not have to imply multiple X11
'screens'. They can, but they don't have to, and it's very rare to
prefer multiple screens.

'Screen' is a jargon term in this context, like 'display' - I'm putting
it in quotes to be unambiguous. If all your applications run with
DISPLAY=:0, or equivalently DISPLAY=:0.0, you have one X11 'screen',
potentially outputting to multiple monitors. If some of your
applications run with DISPLAY=:0.1 and are permanently tied to a
different set of monitors (probably a set of size 1), *that* is a second
X11 'screen'.

If you have multiple LCD/CRT/whatever monitors on one desk, or a laptop
and a monitor, or a laptop and a projector, the option that is usually
preferred is a single X11 'screen' spanning multiple monitors, with
optional runtime switching between mirroring (same content on each
output) and non-mirroring (different content on each output). That's
what Xrandr normally does on modern systems, and as far as I'm aware,
what all current desktop environments optimize for. It's also the X11
equivalent of all the supported arrangements in Windows and OS X.

For instance, on the laptop where I'm typing this (with Intel HD
graphics, as it happens), here's what my output looks like:

|----------|
| monitor  ||--------|
|          || laptop |
|----------||--------|

DISPLAY :0 --- screen :0.0 /-- HDMI2 --- monitor
                           \-- LVDS1 --- laptop

The equivalent with multiple 'screens':

DISPLAY :0 /-- screen :0.0 --- HDMI2 --- monitor
           \-- screen :0.1 --- LVDS1 --- laptop

would mean I wouldn't be able to drag windows to and from the laptop, or
copy and paste between the two screens, and I don't have enough
historical X11 knowledge to know whether I'd need a second keyboard and
mouse for that setup.

>> I have to admit that the Linux / X window (and successor) terminology
>> confurses me--when I say multiple screens, I mean multiple monitors
>> driven by
>> a single PC and different content on each, and, ideally (but not
>> always the
>> case) the ability to move content between displays and copy and paste
>> to and
>> from each.

It sounds as though rhkramer may be one of the people Michal is thinking
of, who has been confused by the unfortunate historical terminology,
does want multiple monitors, but does not necessarily want multiple of
the historical X11 construct whose jargon term is 'screen'.

> I appreciate the vote of confidence.  Perhaps "separate X screens" is
> something which only a small percentage of user are multi-tasking enough
> to take advantage of. However, I am one of them.

>From other emails, it sounds as though you (for disambiguation: Ken) are
one of the minority that genuinely does want multiple X11 'screens',
with no copy/paste between them, and no ability to move windows between
them. I'm not sure how this actually improves your experience when
multi-tasking when compared with a Xrandr-style large 'screen' spanning
multiple monitors, but "you asked for it/you got it"[1].

However, this is a sufficiently small minority that it seems reasonable
to ask "are you *sure* this is really what you're looking for?" when
someone asks for it, because it's fairly common for people who are
confused by the terminology to think they want multiple (jargon)
'screens' for their multiple (non-jargon) screens, even though that
leads to reduced functionality.

If your goal is to have immovable displays appearing on particular
monitors, that's also possible to achieve within a single 'screen' by
modifying or configuring a window manager or compositor to place windows
where you want them. (For instance, tiling window managers like
Awesome[2] tend to support this sort of thing.)

-- 
Simon McVittie
Collabora Ltd. <http://www.collabora.com/>

[1] the lesser-known opposite of WYSIWYG
[2] http://awesome.naquadah.org/wiki/Using_Multiple_Screens