Drag and drop surfaces not always showing with multiple outputs

[ids1024]

I'm still trying to figure out exactly what is causing this. I've noticed it testing pop-os/cosmic-workspaces-epoch#101. It seems to work fine on anvil and sway (using the mock-backend feature) so this appears to be an issue in cosmic-comp. With Smithay/client-toolkit#477 I'm able to reproduce this in a more minimal case; again working on other compositors.

This only happens with multiple monitors, doesn't happen in anvil, and is inconsistent, so I think it's some race condition related to multiple kms threads trying to draw the same surface.

COSMIC_DISABLE_DIRECT_SCANOUT=1 seemed to fix this in cosmic-workspaces, but in the sctk example I've seen it with that as well. So maybe that's just changing the timing of a race condition...

In the sctk example, when a drag doesn't show a drag surface, moving the cursor to another output sometimes, but not always, makes it appear. Regardless, the drag works, it's just the surface isn't rendering.

This doesn't seem to be related to the damage returned by the WaylandSurfaceRenderElement, since I still see it after changing that to always be non-empty.

[Drakulix]

Does this maybe fix it? #1080

[ids1024]

Behavior seems largely the same after that. The data_device sctk example still sometimes but not always shows the drag surface.

[Drakulix]

Behavior seems largely the same after that. The data_device sctk example still sometimes but not always shows the drag surface.

I'll try to replicate and debug this then.