headless wayland sessions, wayland apps displayed to apps

[Pekka Paalanen]

On Mon, 3 Dec 2012 19:02:06 -0500
David Jackson <djackson452 at gmail.com> wrote:

> With Wayland will we be able to:
> 
> Have multiple seperate wayland sessions on the same computer, as many as
> one wishes,

Yes.

> with many of them being headless, accessible if the user wishes
> through a remote desktop solution such as VNC?

Sure, but that is not a Wayland protocol or libwayland thing. The only
Waylandy thing there is that the (headless) server needs to be a
Wayland server, naturally. Where that server pushes surfaces to and
gets user input from can be anything.

> Will be able to use a
> command line switch or environment variable to determine which wayland
> session an application should be started in on a per application basis?

Yes, it already exists.

> Does the wayland environment provide information on what areas of the
> screen are visible to apps, similar to Expose events? This could also be
> done with a pointer to shared memory data structure that contains a list of
> exposed areas. If this is not provided, I would be concerned applications
> will waste time drawing areas of their window that are not visible.

No.

See wl_surface::frame request[1] instead. Clients always provide
complete frames.

> I previously asked if one can run an rootless and an session in-window X
> Server as a wayland client, to a wayland session, so x applications can be
> displayed on a wayland display, and if one can display a wayland session
> and even individual wayland apps onto an X server. I think that these are
> very important features.

XWayland already exists, and offers at least rootless X app support on
Weston.

Weston can already run on an X server, one X window per Wayland output,
with the x11 backend. That is like rootful, not rootless.

> Being able to display  individual wayland apps to an X server selectable at
> runtime, is a highly desirable feature, this would solve the need for
> headless remote desktop sessions, since I could display wayland apps to
> Xvfb (headless) and use x11vnc with Xvfb.

Not implemented, and I cannot see the usefulness of this in the long
term, but it is definitely possible to implement.

> These features will be necessary. The fact is, toolkits and applications
> cannot be trusted to provide runtime switchable display targets between
> wayland and X11. We've had experience with similar situations that shows
> that application developers will neglect this. Back when XRender extension
> was implemented, a large number of X applications ended up not supporting a
> fallback for servers that did not support XRender, despite the assurances
> that they would. This led to X applications not working at all on servers
> that did not support X render. The situation will be similar this time
> around. A number of applications will neglect support for display to x11.

If you say so.

> Users should not be forced to give up their x11 environment, many of us
> have specially tuned X window manager configurations,  and the way to
> assure that this will not happen is to gaurantee that individual wayland
> only applications can be displayed to an X server through some facility for
> this purpose, allowing us to run wayland applications inside our X sessions
> with our preferred X window manager.

There are no technical reasons preventing you from implementing that,
if the only aim is to get Wayland applications to show up in an X
server. When desktop shell protocols evolve, even the window
decorations might not be a problem.


Thanks,
pq

[1] http://wayland.freedesktop.org/docs/html/