[Webkit-unassigned] [Bug 202269] New: [iOS 13] requestAnimationFrame runs at 90Hz in low power mode

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=202269

            Bug ID: 202269
           Summary: [iOS 13] requestAnimationFrame runs at 90Hz in low
                    power mode
           Product: WebKit
           Version: Other
          Hardware: iPhone / iPad
                OS: Other
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Canvas
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ashley at scirra.com
                CC: dino at apple.com

On iOS 13 / 13.1, requestAnimationFrame runs at 90 Hz when low power mode is enabled.

Demo URL: https://www.scirra.com/labs/bugs/safari13raf/index.html

Steps to reproduce:
1. Ensure low power mode is disabled
2. Visit demo URL in Safari and observe FPS reading is 60 (tested on an iPhone 7 Plus, which has a display rate of 60 Hz)
3. Go to settings and enable low power mode
4. Switch back to Safari

Expected result:
FPS reading either the same or dropping to 30 (as I believe previous releases did)

Observed result:
FPS reading is now about 90 FPS, which is higher than the display rate of the device.

Originally discovered in this tweet: https://twitter.com/chribbe1/status/1176767527797579776
The issue appears to affect several web frameworks, indicating a general problem with requestAnimationFrame. I suspect a new 30 Hz timer is being set, but the old 60 Hz timer is not cancelled, resulting in adding together to make a 90 Hz callback frequency.

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