Multiprocess rendering in wayland - webkitgtk+

[Iago Toral]

Hi,

I am working on porting WebKitGTK+ to Wayland and we are having some 
difficulties figuring out the proper way to deal with the multiprocess 
architecture introduced with WebKit2.

In WebKit2 we have two processes that are responsible for rendering the 
contents of a webpage. The WebProcess takes care of parsing HTML, 
identifying the various layers that are part of that HTML (that will be 
rendered separately) and the composition of all these layers to create 
the final view of the page. This composition stage is done with OpenGL. 
Once the composition is done, the other process (UIProcess) needs a way 
to access the results of the composition and paint them on the screen.

In X11, this is achieved by having the WebProcess render the 
composition results to an offscreen XWindow and sharing the XWindow ID 
between the two processes. XComposite is used to redirect the XWindow to 
a pixmap. The pixmap is painted in the UIProcess.

As far as we know, there is no API in Wayland to allow two different 
processes to share a surface, so we are not sure if the architecture I 
describe above is currently supported in Wayland.

So I guess my questions are:
- Is there a way to share a surface between two processes?
- If not, is there a way to implement this architecture in Wayland as 
it is now?
- Would it be possible/interesting to add surface sharing API to 
Wayland so that it supports this type of architectures naturally?

We would really love to see WebKitGTK+ fully ported to Wayland and this 
is probably the major obstacle we have at the moment so we are really 
looking forward to seeing the options we have available to make this 
happen.

Also, notice I am adding two colleagues of mine to the CC who are not 
subscribed to this list. If you reply, please remember to keep them in 
the loop.

Iago