[PATCH] drm: two planes with the same zpos have undefined ordering

[Daniel Vetter]

On Thu, Sep 19, 2019 at 11:02 AM Pekka Paalanen <ppaalanen at gmail.com> wrote:
>
> On Thu, 19 Sep 2019 10:18:04 +0200
> Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> > On Thu, Sep 19, 2019 at 9:18 AM Pekka Paalanen <ppaalanen at gmail.com> wrote:
> > >
>
> ...
>
> > > Right, and we are suffering from that confusion already. Should
> > > userspace use ID order if zpos property is not there or not? I have no
> > > idea.
> >
> > Nope. I think the only options for this case are:
> > - file bug against upstream driver so they add zpos
> > - you magically know how planes work on that hw
> > - you don't overlap planes at all
> > - cursor is above primary, that much we can guarantee
> >
> > Yes it's kinda uapi fail we didn't add zpos from the start :-/
>
> Good. Weston does the last two. The confusion did not last long
> enough to let us add code using the object ID to infer stacking order.
>
> Although, Weston does have the assumption that overlays are in unknown
> order between primary and cursor, which now seems false.

I think cursor is always on top, but some of the overlays can be underlays.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch