Apple - Yosemite: Accessibility zoom + multiple monitors = poor performance

This is now fixed in OS X 10.10.2

There is a workaround posted on the Apple forums.


  • The mouse/key entry performance does "feel" significantly better, as does the momentum zoom.
  • Zoom is per-screen, rather than both at once


  • It is still not nearly as performant as it was in Mavericks. The site will still not render at 60fps while zooming.
  • While this workaround does make multiple-screen performance somewhat better in Yosemite, it makes single-screen performance much worse! Single screen performance is already "perfect" using the default "Full Screen" zoom and this is a step backwards.


  • In System Preferences-Accessibility, set the Zoom Style to Picture-in-picture.

System Preferences - Accessibility

  • Click More Options...

System Preferences - Accessibility - More Options...

  • Click Adjust Size and Location
  • You will see a rectangular magnified panel with an "OK" button in the middle. Drag the corners to the upper-left and bottom-right corners of the screen. Click OK.

Now, when you zoom, it is usable, but still noticeably slow.

Best workaround so far:

In System Preferences-Accessibility, select Increase contrast (which will implicitly select Reduce transparency). This seems to improve performance in some circumstances, but it does dramatically affects aesthetics. The slider on is smooth while zoomed in. There are still some circumstances where zooming is a little sluggish, but it is not nearly as bad as before.

Edit: After several hours of running with Increase contrast enabled (and upgrading to Yosemite 10.10.1), I can say performance is now back to an acceptable level.

I'm still not thrilled about having to enable an accessibility feature I don't want or need to improve performance. I really don't like the appearance of Increase contrast: solid black outlines around text inputs & buttons, the zebra-stripe effect on lists, etc. is all a bit jarring coming from the subtlety of OS X.

I tried just enabling Reduce transparency (which gets implicitly selected when you enable Increase contrast) but that setting alone doesn't help: both need to be enabled to see any performance gain.

Screenshot: Normal appearance Normal appearance

Screenshot: Appearance with 'Increase contrast' enabled Appearance with 'Increase contrast' enabled