Dual display in clone mode or extended mode with Weston

[Matheus Santana]

On Thu, Jun 21, 2018 at 5:11 AM, Pekka Paalanen <ppaalanen at gmail.com> wrote:

> 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.
>

I'm curious about what you specifically mean by KMS device. Each graphics
card?

I've just tried Weston with two displays and it worked out on the fly
("extended mode").


> 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.
>

What does CRTC stand for?

>
>
> Thanks,
> pq
>
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>
>

Best regards,
Matheus
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