[winswitch] Question: How does Xpra communicate with X11-apps?

[Antoine Martin]

On 08/02/2020 04:56, Olbert, Nils via shifter-users wrote:
> Hello,
> 
> I am currently doing some research about alternatives to (plain) X11 and stumbled about this project.
> I did some successful tests on my system and checked the wiki, anyways I was unable to find the answer to the following question:
> I wonder if there is a technical overview of how Xpra works, especially how it interacts with X11-apps.
The simplistic answer is that it doesn't interact with X11 apps directly.
In its most common mode of operation, the "seamless" mode, xpra acts as
a compositing window manager: the X11 server where the X11 applications
are running will forward all window updates to the xpra server.
Instead of displaying those windows on the X11 server display, xpra then
forwards the window contents to any client connected.
Obviously, there's a lot more to it than that, but that's the gist of it.
> As far as I understand Xpra uses its own enhanced protocol, but how does Xpra communicate with a "dumb" X11-app which doesn't "speak" the xpra-protocol?
Xpra's own protocol is only used between the xpra server and its
clients. X11 applications should not be aware of it at all.
The connection between X11 applications and the X11 server is the same
as always.
Everything is mediated through the X11 server.
> Does it use an internal Xvfb (or XDummy) to communicate with the applications or does an Xpra-host support both xpra-protocol and x11-protocol? Or is it completely different?
What is "Xpra-host"? Do you mean the xpra server?
As per above, the xpra server connects to the X11 server using the X11
protocol, and to its clients using the xpra protocol.
This allows xpra to support clients that do not have X11 support, ie:
MacOS, Windows, browsers, etc.

Cheers,
Antoine


> 
> Thanks in advance