If a layer cannot be mapped to a plane, make it so all layers under it also fail
plane allocation so that they can be properly composited on the primary plane.
A test was incorrect and has been fixed. Another test had two possible solutions
and has been updated with the one libliftoff yields.
This commit adds special handling for the layer zpos property. Setting it won't
forward it to KMS, instead it will be handled internally.
The plane zpos (either retrieved from KMS if the property is supported, or
guessed from the plane type and ID) is checked during plane allocation to have
the same ordering as the layer zpos. This adds more constraints to the
allocation.
Note that the new constraints are too strict. In case two layers don't overlap,
there's no need for one plane to be on top of the other. See [1].
Also, the new constraints don't account for underlay planes [2].
[1]: https://github.com/emersion/libhwc/issues/3
[2]: https://github.com/emersion/libhwc/issues/7
Closes: https://github.com/emersion/libhwc/issues/4
In case we can't do better than the current best allocation even if we manage
to allocate all remaining planes, we bail out early. However the bailout
condition was incorrect and didn't account for the current score.
Sometimes the properties applied on a layer are missing on a plane. Instead of
making the whole allocation fail, just mark the plane as incompatible with the
layer.
Given a primary plane with zpos=0 and overlay planes with zpos 1 2, we want
first to allocate the primary plane, then the furthest overlay plane, then the
remaining one: 0 2 1.
References: https://github.com/emersion/libhwc/issues/3
If zpos is present, instead of guessing the zpos from the plane type, just use
it. If two planes have the same zpos, we consider their relative position as
undefined.
We don't handle the case where some planes have zpos set but some others don't.
References: https://github.com/emersion/libhwc/issues/4
Many drivers don't expose the zpos plane property. We can guess it from the
plane type though: primary, overlay, cursor. Except some drivers expose
underlays too: underlays, primary, overlay, cursor. Underlay planes don't have a
special type, they are just marked as overlays. To detect them, check whether
their plane ID is less than the primary plane ID.
References: https://github.com/emersion/libhwc/issues/3
