RandR 1.5 "Monitors" and splitting a single physical display

Jack Coulter jscinoz at jscinoz.so
Tue Mar 7 23:56:55 UTC 2017


With version 1.5 of the RandR protocol, "Monitor" objects were
introduced which, according to the documentation:

> • A 'Monitor' is a rectangular subset of the screen which represents a
> coherent collection of pixels presented to the user
> • Each Monitor is be associated with a list of outputs (which may be
> empty).

As I understand it, RandR 1.5 Monitors are mainly intended to handle MST
displays where multiple physical connections to the same display are
required for sufficient bandwidth, and this new extension allows the two
halves of the display to once more be treated as a single display.

I am trying to figure out if it is possible to use this new
functionality to do the inverse; to split a single display into two or
more monitors which would be treated largely independently by window
managers & applications. Thi would be particularly useful for extremely
wide (21:9, or even 24:9 as we're starting to se) monitors, and devices
such as [1] that present a single large display to the host machine, but
send different regions to different downstream displays.

As far as I understand the protocol document, this _should_ be possible
(since Xinerama information now comes from the configured RandR
monitors), but doesn't appear to be the case with the current xrandr CLI:

Initial output of xrandr --listmonitors:

> Monitors: 2
>  0: +*DP-1-1-1 1920/509x1080/286+0+0  DP-1-1-1
>  1: +eDP-1-1 1920/346x1080/194+1920+0  eDP-1-1

Try to split monitor 0 vertically:

> xrandr --setmonitor test 960/254x1080/286+0+0 DP-1-1-1

xrandr --listmonitors:

> Monitors: 2
>  0: test 960/254x1080/286+0+0  DP-1-1-1
>  1: +eDP-1-1 1920/346x1080/194+1920+0  eDP-1-1
Monitor 0 is now correctly half width, using the left half of DP-1-1-1

Try to add a monitor for the right half of DP-1-1-1:

> xrandr --setmonitor test2 960/254x1080/286+960+0 DP-1-1-1
xrandr --listmonitors:

> Monitors: 2
>  0: test2 960/254x1080/286+960+0  DP-1-1-1
>  1: +eDP-1-1 1920/346x1080/194+1920+0  eDP-1-1
Monitor "test2" has replaced the monitor "test" configured above, and
applications are now displayed only in the right half of DP-1-1-1

Is it possible for there to be multiple monitors for a single output, at
least as far as the RandR protocol is concerned, and is support simply
needed in xrandr, or is what I'm trying to do simply not possible?

Kind regards,

[1] http://www.matrox.com/graphics/en/products/gxm/th2go/digital/

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