Dual display in clone mode or extended mode with Weston

[Pekka Paalanen]

On Wed, 13 Jun 2018 17:40:59 +0530
Ashvini Deshmukh <ashvini2781 at gmail.com> wrote:

> Hello All,
> 
> I have read queries for dual display on freedesktop.org
> 
> I need your help in the same context.
> 
> Currently we are creating one application to support multiple displays with
> Wayland.

Hi,

you are developing an application, ok. I assume that means a Wayland
client specifically.

> We are unaware that one compositor will be sufficient for dual display.

Sorry, I don't understand. Are you asking whether one Wayland
compositor could driver multiple displays? Yes, they can in general.
Capabilities will vary between different compositor implementations.

> We need to know about how virtual framebuffer is created per display.

As an application developer, why would you care about that? That is a
compositor internal implementation detail.

Why virtual? Real outputs do not have virtual framebuffers, they have
real framebuffers as far as the compositor is concerned.

> As DRM supports only one compositor,
> How to display same content on second display OR can we have different user
> events on second display monitor.

What do you mean?

If a Wayland compositor supports and has been configured to show the
same content on multiple displays, then it will do that. From a Wayland
client perspective, there is nothing you need to do to have your
window show up on cloned displays compared to a single display case.

By user events, do you mean input events?

It is certainly possible to write a compositor that dedicates one set
of input devices for one display and another set of input devices for
the other display.

Applications are expected to support multiple wl_seat globals (similar
to multi-pointer X in essence). There is nothing else they would need
to specifically support for a compositor that had multiple outputs,
cloned outputs, or divided input devices in any arbitrary way.

I did not understand your requirements well enough to say how well
Weston would work for you.

For example, Weston currently does not support multiple KMS devices,
but it does support multiple displays on a single KMS device. Support
for multiple KMS devices is desired in Weston though, so maybe it will
in the future.

Weston's clone mode is currently limited to sharing a CRTC between all
displays, assuming someone reviews the final patch needed to configure
it. Support for this configuration does not seem to be common among PC
graphics hardware, embedded boards may have better chances.


Thanks,
pq
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