[GSoC] Some questions about wayland clients with no outputs present

[Eugen Friedrich]

Hi Armin,

first of all I wish you existing and successful project experience!

About the missing output for clients, have just an idea: how about creating
some fake output object, maybe defined in weston.ini and send this to the
clients.
Client needs also the information that current output is a fake output in
order to decide what to do: just continue or wait for a real one.
Compositor could just pass the buffers that are arrived on the fake output
to the real one, ones its available.

Just an idea.
Am 30.04.2016 5:20 nachm. schrieb "Armin Krezović" <krezovic.armin at gmail.com
>:

> Hi all,
>
> Now that I've analyzed the weston codebase a bit, I'm ready to
> bombard you people with some questions :).
>
> For those that aren't yet aware, I'll be working on making weston
> able to run with no outputs and survive with all outputs plugged
> out at runtime.
>
> For starters, I've simply commented out the output backend load code
> in src/main.c to see what would happen. To my surprise, the compositor
> didn't crash, but the desktop-shell did.
>
> I'm currently guessing that it crashes because the clients that use
> clients/window.c code look for outputs in the registry. Of course,
> there are none because the backend that updates the global registry
> isn't loaded.
>
> Now, my conclusion is: In order to make weston work without any outputs
> present is to make clients work without any outputs present. This will
> probably require people to update their toolkits and apps.
>
> As I've originally proposed, I see two different ways in achieving this:
>
> First and easiest way is use of a virtual output. I could modify the
> DRM backend to add a virtual output if no physical outputs are found
> and remove the output when a physical output is connected. Add similar
> behavior on phyisical screen unplug. If there are none left, add a virtual
> output. If I remember correctly, Pekka once noted that DRM backend already
> supports output hotplugging, more or less, but it doesn't support the
> primary output unplugging.
>
> Now, the first question is: Even if this way is picked, would clients or
> something else require much work to make them behave correctly when
> the primary output is unplugged?
>
> The second and more harder way is to simply cope with no outputs present
> and
> watch for output plugging/unplugging. This would require clients to watch
> for
> output changes and take apropriate action.
>
> The second question then might be: What should clients do in such case?
>
> 1. Do they only need to schedule redraw and toggle back fullscreen if it
> was on?
>
> 2. Do they need to resize/scale relative to the size of new screen? (eg, a
> maximized
> app on 1920x1080 screen would not be entirely visible on 1600x900 one).
>
> 3. Is there something as "move an app to different screen" that can be
> issued
> by compositor? Or do apps need to do that too?
>
> 4. Is there anything special needed for XWayland or is it just another
> wayland client?
>
> That would be all for now.
>
> Armin.
>
>
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>
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