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

[Simon Ser]

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