Update: Apple has officially responded that some of the behaviours described below are the result of an OS bug. Full support for 120Hz in third-party apps is coming soon. Original story below.
That means the iPhone 13 Pro models feature new OLED displays that can refresh their screen content at up to 120 times per second, or 120Hz. However, developers receiving their phones today have discovered that, in many circumstances, their animations can only run at 60Hz — the same as the cheaper iPhone 13 and iPhone 13 mini, as well as prior iPhone generations.
As it stands with iOS 15.0, ProMotion takes effect in third-party apps when scrolling or doing full-screen transitions. That means that you will still get a very fluid and responsive experience when scrolling your Twitter timeline, for instance.
However, almost all other animations are capped at 60Hz in third-party apps. This includes special effects and animations for custom components. It can be particularly jarring for the same third-party app to feature smooth scrolling but then less-smooth interaction experience elsewhere. Developer of the Apollo Reddit client Christian Selig has already reported complaints about this from his customers.
A workaround hidden plist-key has been discovered that lifts the limit for SceneKit and SpriteKit based applications, and Dice by PCalc developer James Thomson is currently seeing if it will pass App Review. However, most animations in iOS apps are driven by the Core Animation framework and remain limited to 60Hz, even in the presence of this special undocumented plist entry.
Interestingly, these limits do not apply to third-party apps running on the iPad Pro, which has featured a 120Hz display since 2017.
Apple appears to have specially carved out these restrictions for the new iPhone models. One source suggested that this had been implemented for battery life reasons. However, we don’t know for sure if that is the case.
Perhaps more conspiratorially, examination of iOS 15 code indicates that only third-party apps are being constrained. Code in the OS exempts first-party Apple apps and allows them to run at full 120Hz animation speed all the time.
Apple touts ProMotion on the iPhone as an adaptive system that ramps up and ramps down depending on what the user is doing. For instance, if the screen is dormant, the phone can lower itself to a 10Hz refresh rate to save power. However, customers and developers reasonably expected that app animations would be able to take advantage of the 120Hz hardware for super fluid animations, just like they can get with scrolling. Apple’s apps certainly seem allowed to do just that, as all apps can on the iPad Pro, but not third-party apps on the iPhone 13.
It’s still possible this is all just a bug in the 15.0 implementation, but it sadly seems unlikely in the presence of the code evidence. We’ve contacted Apple about this situation for clarification and will update if we hear back.
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