Remove outputs when switching away from VT

[emersion]

When switching away from VT, remove the wlr_outputs (same as unplug). When switching back, re-add them (same as hotplug).

This would avoid connector/CRTC state inconsistencies (e.g. how to modeset when DRM FD is paused). This would be consistent with input devices.

---

wlroots has migrated to gitlab.freedesktop.org. This issue has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/2370

[ammen99]

This would require the compositor to keep track of which output each view is on and restore that. Wayfire currently doesn't do it :/
How would it work in Sway (if it works at all)?

[emersion]

Ah, yes, that is correct. I just assumed everybody does it.

Sway migrates workspaces from one output to the other, and keeps a list of "output priorities": https://github.com/swaywm/sway/blob/6991ac8c70869ca19a87cfc173e280cab7ff20d0/include/sway/tree/workspace.h#L42

[agx]

just for the record: phoc doesn't (yet) keep a list either but that's on the todo list.

[ammen99]

One naive question: Why can't the DRM backend just reinitialize the outputs without unplugging and replugging them?

[emersion]

The problem I'm trying to fix is that things are weird when switching VTs:

• All operations on the output are invalid: can't page-flip, can't modeset, can't enable/disable, etc. IIRC right now the DRM backend fakes success (and defers till next VT switch) and that's not great (maybe the deferred operation will fail and put the output in a bad state).
• I don't want the DRM backend to change output state behind the compositor's back
• Outputs can be unplugged and hotplugged, but the compositor won't notice it
• Other compositors might change the output state