Wayland / Weston Multi Display Client-Side Functionality

Scott Anderson scott.anderson at collabora.com
Mon Feb 25 11:11:45 UTC 2019

On 25/02/19 8:21 pm, AMAR SEN wrote:
> Hi,
> 1. Is there any client side functionality to handle multiple displays? 
> It can be seen as like a particular client has some options that can 
> direct the server to show frames on either of the displays or both 
> (multiple displays) of them at the same time. If it has such 
> functionality, can somebody point me to an example implementation of 
> such client?

A normal Wayland client has no control regarding how it is placed by the 
compositor, which is an intentional design decision.
The most control I can think of (which may fit your use case), is that a 
client can ask to be placed fullscreen on a particular output using the 
fullscreen-shell protocol

> 2. As I have read at multiple places that weston supports multi-display 
> for drm based devices, is it also possible for fbdev backend, or it has 
> some functionality constraint that do not let that to work on fbdev?

I _think_ the fbdev backend does support multiple outputs. I've never 
actually used the fbdev backend before, but the code implies that it 
does. Either way, I would strongly recommend that you use the DRM 
backend instead.

> 3. I am actually using weston-3.0.0 version for my project, does it have 
> multi-display support for any backend? If yes, can someone please help 
> me findĀ  the commit to the wayland weston project which brought in the 
> multi-display support?

Just to be absolutely sure, are you just referring to having multiple 
computer monitors ("heads") connected? I believe weston has always had 
support for that.
Later versions of weston are capable of cloning a monitor's contents 
efficiently across multiple monitors, which may potentially be useful 
for you.

> Thanks,
> Amar Sen

If you require more complex control of how Weston does window 
management, writing a Weston plugin would be the way to do that, as 
opposed to a client trying to take control (which it can't).


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