[Wayland-bugs] [Bug 101681] How to find which DRI version is used by Wayland, and what is the method to change DRI version on Wayland?

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101681

--- Comment #5 from Daniel Stone <daniel at fooishbar.org> ---
(In reply to _nobody_ from comment #4)
> The primary reason I posted this Bugzilla was to help Sam. But I had aside
> agenda as well. To better understand the whole Xorg server and Wayland
> server  architectures, which you greatly contributed to it/understanding! :-)

Glad to hear it. :)

> And here is what I got from your explanation.
> 
> [1] Regarding X11 clients and Xorg server I am correct, as I see;
> [2] For Wayland clients, the following picture shows correct relations
> between Wayland clients and Mesa, which beneath has something lookalike DRI3
> implementation for the 3D applications:
> https://upload.wikimedia.org/wikipedia/commons/a/a7/
> Wayland_display_server_protocol.svg

Indeed.

> [3] I missed point where X11 client has to connect to Wayland server, if
> Wayland is chosen as server. in such a case, Wayland will continue to
> support legacy Xorg server architecture, but ONLY for DRI3. In other words,
> backward compatibility for X11 clients on Wayland server is supported, but
> ONLY for DRI3.

In that case, the Wayland server starts a separate process, called Xwayland.
Xwayland is an X11 server and a Wayland client: X11 clients connect to Xwayland
(sending buffers over DRI3), and Xwayland then forwards those buffers to the
Wayland server. So X11 clients do not know the difference (they connect to a
real X11 server), and all the translation between X11/Wayland is done inside
this server.

It is _in theory_ possible for Xwayland to implement DRI2 for X11 clients, but
this is much more work than just fixing DRI3 for you; also fixing DRI3 has a
larger benefit for everyone.

> One more question for you, Daniel, if you allow: do you guys, allow Wayland
> clients to run with Xorg server? I assume the answer is NO (forward
> compatibility for Wayland clients on Xorg server is not supported)?

Right, so far there is no kind of reverse-Xwayland. The closest equivalent is
running Weston/Mutter/etc under X11, but this is not seamless in the same way
that Xwayland is (i.e. showing the clients as part of your regular desktop). I
probably wouldn't expect there to be either.

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