Developers earlier this week have begun to notice that third-party apps were not able to run at 120 frames per second on the iPhone 13 Pro’s ProMotion display which offers a variable 120Hz refresh rate. Even though ProMotion worked while scrolling or using full-screen transitions, most animations on third-party apps were locked at the standard 60Hz, including special effects and pop-up menus.
The resulting experience was described as jarring, seeing as how scrolling through the affected apps was “twice as smooth” as the apps’ other animations. Christian Selig, the creator of a Reddit reader app called Apollo, is one of many developers that have brought this issue to light:
Am I correct in seeing that UIView.animateWithDuration APIs aren't clocked at 120Hz on iPhone 13? On UIScrollView, system ones, and Metal by the looks of it, rest is still 60Hz? pic.twitter.com/t3MeM9cj0E
— Christian Selig (@ChristianSelig) September 24, 2021
What’s more peculiar is that this limitation does not seem to apply to apps on the iPad Pro, which has had a 120Hz-capable display since 2017. In response to this issue, Apple has updated the developer documentation clarifying that all apps are actually able to take advantage of ProMotion.
To achieve that, developers need to add a custom key that has been specified by the documentation into a file called Info.plist to opt-in for the higher refresh rates. The company also added that there is a bug affecting some animations built using Core Animation and that a fix is coming soon in an update.
Both the new iPhone 13 Pro and the larger iPhone 13 Pro Max feature the Super Retina XDR OLED display with ProMotion, which is Apple’s name for its adaptive refresh rate screen. The display can use anywhere from a maximum of 120Hz and go all the way down to 10Hz when not in use, which saves on battery life. In Malaysia, all models within the iPhone 13 and iPhone 13 Pro family will be available for pre-order on 1 October while general rollout will take place one week later.
(Source: Apple Developer Documentation via 9to5mac.)