Apple finally brought its ProMotion adaptive refresh rate technology to the iPhone with the release of the iPhone 13 Pro. The latest model’s Super Retina XDR display will allow developers to make their animations seem as smooth as possible thanks to its peak 120Hz refresh rate—at least in theory. It turns out supporting the new ProMotion display requires a bit of finagling.
A new guide called “Optimizing ProMotion Refresh Rates for iPhone 13 Pro and iPad Pro” explains how app developers can adapt their apps to the new-to-the-iPhone display technology. (ProMotion has been part of the iPad Pro lineup since 2017.) But at least part of that process will require those developers to accept that Apple doesn’t offer much control over ProMotion.
“You can’t force a ProMotion display to show your content at any specific rate,” Apple said. “The refresh rate of a ProMotion display behaves differently than a traditional display. The system insulates the ProMotion’s actual refresh rate from your app.” Developers can merely “provide hints to Core Animation about what refresh rates the app prefers for its animations.”
That means developers are supposed to optimize the animations in their apps for refresh rates and timings that range from 10Hz (100ms) to 120Hz (8ms) on the iPhone 13 Pro lineup and 24Hz (41ms) to 120Hz (8ms) on the iPad Pro. All told there are 12 different refresh rate and timing settings on the iPhone 13 Pro and five different settings on the iPad Pro to support.
“Custom animations in your app need to be able to adapt to changes in refresh rates,” Apple said. “Display refresh rates can change for many reasons and your app must not presume any specific refresh rate, at any time. For example, the system disables faster refresh rates in low power mode or if a device gets hot.”
Those are just the animations themselves. Adding support for ProMotion to an app also requires modifying the app’s Property List File (.plist) on the iPhone 13 Pro as well as properly implementing a variety of Apple-provided frameworks, classes, and other operating system-level technologies over which the developer has limited control at best.
Apple said that some apps “may already be capable of taking advantage of these new refresh rates without any changes” on the developer’s part thanks to the UIKit, SwiftUI, and SpriteKit frameworks as well as the “abstract superclass for animations in Core Animation” called CAAnimation. (Though it seems that still requires the .plist modification on iPhone 13 Pro.)
All of which means that enabling support for the iPhone 13 Pro and iPhone 13 Pro Max’s new adaptive refresh rate display won’t be as simple as flipping a switch, and even when developers implement everything properly, the system can decide not to support a higher refresh rate because of Apple’s concerns about battery life and operating temperatures.
