OpenGL vsync bug in macOS Ventura affects frame flip detection in PsychoPy

There is an OpenGL vsync bug in macOS Ventura 13.0 and 13.1 that affects vsync detection in PsychoPy. If you run “” or “” (see Demo->timing), you will see dropped frames and a mean win.frameIntervals that is incorrect (shows an odd bimodal distribution). For example, on a 60 Hz iMac monitor it shows a mean of 8.27 ms, whereas it should be ~16.67 ms.

OpenGL vsync detection works fine in macOS Monterey (tested on Intel and M1 Macs). Thus, best to avoid macOS Ventura when running PsychoPy experiments on a Mac until this bug is fixed (hopefully in macOS 13.2).