Dual display in clone mode or extended mode with Weston

[Matheus Santana]

On Thu, Jun 21, 2018 at 3:44 PM, Matheus Santana <embs at cin.ufpe.br> wrote:

>
>
> 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?
>

Found the response for this in SoC ideas page
<https://www.x.org/wiki/SummerOfCodeIdeas/>:

Weston supports multiple outputs, but currently limits them to a single
> GPU. Add support to Weston's DRM backend to open several KMS devices, with
> the ability to use outputs from all of them.
>


>
> 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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>> wayland-devel at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/wayland-devel
>>
>>
>
> Best regards,
> Matheus
>
>
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