scene: add support for damage tracking

[emersion]

Introduce wlr_scene_output to have per-output state in the scene-graph.

I've decided to not make wlr_scene_output a wlr_scene_node to make a clear cut between elements that are rendered on screen and viewports in the scene.

Depends on: #1966
Cage patch: cage-kiosk/cage#203

[emersion]

This is ready for review.

[ifreund]

I wonder if any compositor that doesn't already use wlr_output_layout will use the scene graph API. It seems like some integration there could save almost every compositor some boilerplate.

[emersion]

I wonder if any compositor that doesn't already use wlr_output_layout will use the scene graph API. It seems like some integration there could save almost every compositor some boilerplate.

Yes, likely, but I'd prefer to keep this as a separate patch (feel free to submit a PR built on top of this one!). One still unanswered question is how we should plug existing wlroots modules to the scene-graph. Should the scene-graph add support for wlr_output_layout, or should wlr_output_layout add optional support for the scene-graph? In other words, should we have wlr_scene_create_with_output_layout(output_layout) or wlr_output_layout_create_with_scene(scene)? (API subject to be tweaked a bit to allow better extensibility.)

[ammen99]

wlr_output_layout_create_with_scene(scene)

Would this support NULL scene? In Wayfire, I'd like to use wlr_output_layout but not scene for obvious reasons ..

[emersion]

Yes, of course. output-layout and the scene-graph will both stay optional and compositors will still be able to use one without the other.

[emersion]

Rebased on top of @djpohly's #3140.

[djpohly]

Something is off with wlr_scene_output positioning. Here's the scene-graph example running Alacritty:

I added the line

wlr_scene_output_set_position(output->scene_output, 30, 10);

and - if I had to guess - it looks like the damage rectangles are correctly translated with respect to the viewport, but the rendered surfaces are missing a pair of minus signs somewhere.:

[emersion]

Something is off with wlr_scene_output positioning

Indeed, must've missed something in a refactoring. Fixed in "scene: fix wlr_scene_render_output offset".

[djpohly]

Here is a MWE for another issue I'm seeing. Run on DRM backend, move the (invisible) mouse cursor to generate redraws, notice the flickering rectangle, and click to exit.

I'm still not very confident in my understanding of double-buffering and damage, but it looks like... maybe existing bits of scene aren't ending up being rendered to one of the buffers when a new output is created? I'm not actually sure whether the problem is specific to the scene-graph code.

[emersion]

Indeed, what you're seeing is a wlr_output_damage issue, fixed here: #3175

[djpohly]

Not sure whether this belongs here or there, but with #3175 applied, I still get the behavior when the scene_output is created after the initial output_commit (MWE).

[emersion]

I've updated this branch to call wlr_output_damage_add_whole in wlr_scene_output_create to make sure this doesn't happen. Have you fetched the latest force-push from this branch before applying #3175?

[djpohly]

It's possible that I missed that push. I'll give it a full recheck and report back.

[djpohly]

Guess this one was PEBKAC - sorry about that! (I'm still trying to track down another issue with what looks like the wrong regions being damaged on my second monitor, but I don't have anything too useful yet.)

[bl4ckb0ne]

LGTM!