drm: transform plane damage to framebuffer-space for FB_DAMAGE_CLIPS

[Ph4ntomas]

Description

Right after rendering, DrmCompositor build a PlaneDamageClips object, which is used to populate the FB_DAMAGE_CLIPS plane property. This property may be used by drivers to repaint only the damaged part of the plane, and is expected to be a bunch of rectangles in framebuffer coordinate-space. Current implementation uses the render_damage directly, which are transformed following the output_transform. If the device driver respect the FB_DAMAGE_CLIPS and only repaint those areas, this breaks rendering for any transform but normal since the actual damage and the reported one are misaligned.

Fix: apply the output inverted transform on the damage rectangle before passing them to PlaneDamageClips::from_damage.

Fixes: #1651

Note for review

There are two things I'm not 100% sure about this PR:

1. I went to the change with the least possible side-effect, so damages are transformed to framebuffer-space at the last possible moment. I'm unsure if the transform should be applied to the Vec returned to calling code. My gut feeling is that it shouldn't however.
   Transforming the damage in damage_bag.render_output would fix winit backend in anvil for free, but also introduce a lot of side effects (I don't think I've seen any code re-transforming the damages returned by that function), but I'd like to have someone else input on this.
2. Size for the transform area is output_geometry.size because that's what has been used in damage computation.
   I'm unsure if it's should be changed to config.properties.dst which is the un-transformed output size (and would need an additional transform). As far as I can tell, the two are equal anyway, so output_geometry.size felt like a good fit.

EDIT: There's a second call to PlaneDamageClips for direct scanout, which might require some changes too. I haven't managed to hit that code while testing yet. I'll add a commit if I do and it's buggy.
EDIT 2: Well, still haven't hit that code, but I think element_config() does the right transformation before building the PlaneDamageClips.

Checklist

• I agree to smithay's Developer Certificate of Origin.

[tux-linux]

This fixed the issue we had on Quill OS with portrait mode not working. It was previously described here: niri-wm/niri#2741
Since niri does not yet seem to support the latest smithay commits, I found it was easier just making a new commit with this commit's contents on our forked branch to make things work for now.

Kind request: if everything passes your tests and requirements, please merge the PR when it's possible for you. Thanks!

[Ph4ntomas]

Ping @cmeissl, IIUC you're the one dealing with most of the DRM stuff.

Do you mind having a look whenever you have some time?

[cmeissl]

Thanks for working on this!

[cmeissl]

Thanks!