[Wayland-bugs] [Bug 83881] Generic dmabuf protocol

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=83881

--- Comment #8 from Nicolas Dufresne <nicolas.dufresne at collabora.co.uk> ---
(In reply to Benjamin Gaignard from comment #6)
> Which GStreamer video sink do you use as client ?
> How do you allocate the buffers in this sink ?

The GStreamer part should probably be discussed here.
https://bugzilla.gnome.org/show_bug.cgi?id=711155

I'll try to comment base on what should concern wayland, adding a little
context. In GStreamer there will is two possible display element working on
Wayland, glimagesink and waylandsink.

glimagesink uses client side EGL/OpenGL/GLES2 to render the video. It will most
likely never allocated DMABUF, but will most likely be able to import them.
This can already be implemented without any changes to current Wayland
protocols.

waylansink, uses wayland specific representation for wrapping video memory.
It's a smarter choice, since it gives the compositor the choices of the
smartest renderer. Adding DMABUF in this case requires protocols. The patches
submitted at the beginning of the year were not merged because of open issues,
including usage of driver specific APIs and that this new protocol was still
changing very quickly. What has been proposed to Benjamin was to focus on
getting importation of DMABUF first, and come back with allocation when this
problem get resolved in a better way. The allocation of DMABUF remains an open
issue for everyone.

A small comment though, if we want this work to be usable in waylansink. By
it's nature, the alignment of a DMABUF frame received might not match the
required alignment by the GPU or HW mixer, or any HW involved. A miss-match
should never prevent the rendering of a buffer unless the buffer is not
mappable to user space. This is often not so simple as only kernel space can
figure-out there is a miss-match (at least at the moment). It is important to
handle this nicely and manage non-destructive fallback.

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