Full-motion zero-copy screen capture in Weston

[Simon Ser]

On Friday, May 31st, 2024 at 16:45, Simon Ser <contact at emersion.fr> wrote:

> > See: https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/124
> > 
> > > My goal is to implement this screen capture with a guarantee that the copy comes from a KMS writeback connector. I know this sounds like an odd thing to insist on. Let's say that in my industry, the system is rarely only running Linux directly on the bare metal. Using the writeback hardware on the display controller allows to get a copy of content from all the virtual machines in the system.
> > 
> > Although the protocol is called "screencopy", it does not need to be
> > implemented via copying. I don't think anything precludes drm
> > write-back or rendering directly to the client-submitted buffers.
> 
> Not sure that's true… With screencopy the client necessarily provides
> buffers that the compositor copies into.

Correction: Andri said that it should be possible to pass client-allocated
buffers to the writeback connector. There might be allocation considerations
to take care of, but it might work fine indeed.