[Intel-gfx] [PATCH v3] drm/i915: add immutable zpos plane properties

[Simon Ser]

On Thursday, April 18, 2019 8:20 AM, Simon Ser <contact at emersion.fr> wrote:
> On Wednesday, April 17, 2019 11:35 PM, Simon Ser contact at emersion.fr wrote:
>
> > In terms of graphs, if a plane is a node and a two-plane overlap is an
> > edge, it means we want a complete graph (each node has an edge to all
> > other nodes). If we only have square planes, it's already impossible to
> > get a solution for 4 planes (the graph contains an edge that crosses
> > another edge [1]).
>
> The following is only true if all planes have an identical size (the
> transformation from planes to the graph is lossy otherwise). It's
> possible to choose different plane sizes and still be able to find a
> solution without an alpha channel for 4 planes [1]. Thanks Léo Andrès
> for pointing this out!
>
> Will investigate a little bit more, to see if I can find a general
> formula for n planes.
>
> [1]: https://www.zapashcanon.fr/~leo/lohi2.png

Discussed with Ville, and this solution won't work as older hardware
doesn't have an alpha channel for overlay planes.

Discussed with Martin, and the most reasonable solution seems to keep
it simple and draw as many frames as there are planes. Frame i would
show plane i as fullscreen and all planes but plane i as small
squares on top or under it. This simple approach makes it easier to
debug and still uses just a few frames.