John SiracusaMar 31, 2023

I've been tracking this one down for a few days. Ever since I updated to macOS 13.3, window dragging sometimes looks like this.

It happens with any window in any app. It stops when I hide some(?) other windows. Not sure why and which windows, but I'm working on it…

Show threadJohn SiracusaApr 24, 2023

Here's a better screen recording of the laggy-window-dragging bug I described earlier (currently filed with Apple as FB12122106)

https://youtu.be/h0bKmcsMFvw

FB12122106 Demonstration

YouTube
Show threadSteve Troughton-SmithApr 24, 2023
@siracusa that jittering tells me some other process is trying to update the window position as you're dragging it
Show threadJohn SiracusaApr 24, 2023
@stroughtonsmith I’ve been assuming it’s the snap-to-window-edge feature that was added to macOS several years ago, but somehow going haywire since 13.3 was released.
Show threadSteve Troughton-SmithApr 24, 2023
@siracusa I would be very surprised if it’s not at all related to third party software. It looks like something is looping over your window list and reading/setting frames 👀 I can open a hundred TextEdit windows here without seeing any slowdown to snap, and I'm just on a Mac mini
Show threadJohn SiracusaApr 24, 2023
@stroughtonsmith It started immediately after I updated to macOS 13.3, so if it’s third-party, then it’s a third-party conflict with 13.3.
Show threadSteve Troughton-SmithApr 24, 2023
@siracusa could be something like the window list API changed internally to something slower than before, another one of those 'hope nobody notices' things?
Show threadJohn SiracusaApr 24, 2023
@stroughtonsmith Maybe, but then what’s reading the list? And if it’s the window server (or WindowManager) then why isn’t it happening to everyone? Mysterious. I will continue investigating…
Show threadChris Turner
@siracusa have you tried doing an strace (or whatever the macOS equivalent is) of windowmanager with and without the bug occurring? it would be a lot of output to mull through but you might see a difference that could be helpful
Apr 25, 2023 at 1:27amWeb
Show threadChris TurnerApr 25, 2023
@siracusa looks like it’s dtruss and you need to disable SIP to use it. Meh. If I can manage to reproduce on one of my macs I’ll try it and report back.
Show threadJohn SiracusaApr 25, 2023
@megachris sc_usage and fs_usage can get you a lot too, but I already did spindumps which cover a lot of the same area.