What is wesron_plane?

[Pekka Paalanen]

On Fri, 04 May 2018 19:32:44 +0000
Sichem Zhou <sichem.zh at gmail.com> wrote:

> Hi all,
> 
> Many data structure in libweston is straightforward, but I don't really
> know what does weston_plane do in the compositor. As it seems I don't need
> to deal with it alot. It seems that it's a abstract place to stack
> `weston_output` and `weston_views`. Like a virtual plane to draw all the
> outputs on it. What is the relationship between `weston_plane`,
> `weston_view` and `weston_output`?

Hi,

weston_plane is an intermediate compositing entity to support
hardware overlays. A backend uses the display hardware to composite
several weston_planes for a single weston_output. A backend uses a
renderer to composite weston_views into the primary weston_plane.

For one weston_output, if the backend implements the assign_planes
hook, the backend may lift some weston_views from the primary
weston_plane to additional weston_planes. On the additional
weston_planes, the renderer is not supported, and there is assumed
to be at most one weston_view to one additional weston_plane, to be
shown by hardware overlays.

weston_planes are manipulated by the libweston backends, and never
by libweston users.


Thanks,
pq
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