Following initial testing of iOS 15 that found many third-party apps could not exceed the standard 60Hz refresh rate of the screen, Apple has now clarified the situation. The good news is that developers will be able to take full advantage of the 120Hz ProMotion display soon.
Apple says that developers will need to add a new Info.plist key to opt-in, and documentation is coming soon. In addition, a forthcoming software update will resolve a bug where animations driven by Core Animation were not able to reach the fluid 120Hz refresh rates.
Standard animations and scrolling interactions are automatically enhanced by ProMotion without developers having to write any custom code. This includes the power efficiency savings when the screen can ramp down to 10Hz, not just maxing out at fluid 120Hz.
For battery life reasons, apps will need to opt-in to 120Hz support if they are doing particular custom rendering, like games.
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