Implement root_change

[Monsterovich]

This also fixes the crash when the root window size has changed which caused the backend to be destroyed.

[absolutelynothelix]

this change makes xrender and dummy backends segfault.

[Monsterovich]

this change makes xrender and dummy backends segfault.

I added a check for root_change, because it's not present in these backends (there should be some implementation at least in xrender, idk).

[yshui]

not commenting on whether this is something we want to do, but this change only masks the real problem: stale flags when the backend is destroyed. we need to investigate why that's happening.

[Monsterovich]

not commenting on whether this is something we want to do, but this change only masks the real problem: stale flags when the backend is destroyed. we need to investigate why that's happening.

I honestly don't know why this is happening either. Maybe if we resolve the misuse of deinitialization, it will "fix" itself.

Because I always use unredir_if_possible and I don't see this assert crashing every time.

[yshui]

it will "fix" itself.

i don't think this is a good attitude towards bugs.

[Monsterovich]

i don't think this is a good attitude towards bugs.

Yeah, well, try to catch a bug that pops up once a week.

I'm sure that's not the only reason, in this ticket I was catching the same crash in this assert when just switching windows but only in a specific program.

[haarp]

fwiw, I can reproduce the Stale flags set for mapped window 0x0123456789 during backend destruction bug almost daily. It seems to happen when the machine wakes up from suspend to a different monitor layout and then everything goes bonkers trying to set up monitors while the screensaver tries to keep stuff hidden.

Will try this patch.

[Monsterovich]

Will try this patch.

I have this patch fixing this problem entirely, and I've been running this patch for months now. Without it, picom is unusable for me.

[haarp]

Haven't had anymore crashes when changing the monitor layout with this patch. Thanks! Would be great to get it merged :)

fixed