The reason for those smooth iPhone X gestures? 120Hz touch input sampling

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Before actually getting to use the iPhone X last week, we were a bit on the fence about its new gesture-based navigation of swiping up, holding, or flipping through recent apps. Could these really replace the simple act of tapping the legacy home key? 

Our worries, it turned out during the review process, were in vain. Not only are the gestures very intuitive, and easy to become second nature, but also the sheer responsiveness of the display while executing those made us wonder what could be behind the smooth operation. We din't encounter a stutter, slowdown or skipped animation framing once, even with plenty of processes kept in the background.

Well, remember those rumors that the iPhone X will sport the same ProMotion display refresh technology that is available on Apple's newer iPad Pros? ProMotion is Apple's marketing name for doubling the typical 60Hz refresh rate of a mobile display, and that 120Hz refresh makes everything scroll, swipe and animate smooth as silk. The upcoming Razer Phone does that, too, and it is one of the crown jewels in its gaming street cred. 

The iPhone X, however, doesn't have a true ProMotion 120Hz display refresh rate, so how come the gesture response is so instantaneous? What the iPhone X does have, is the next best thing  - a 120Hz touch sampling rate, as you can see in Apple's developer support table below. It means that when you place your finger(s) on the display, it refreshes with double the usual rate, ready to follow every flick and whim of your fingertip(s) with lightning speed, then throttles things down to the normal rate to save on tasking the graphics subsystem and the battery. Could this be the reason for the touch layer freezes in cold weather temps? It remains to be heard, but Apple promised a software fix, so that might have something to do with it.

Or, as Apple puts it for its developers: "When the capture rate is higher than the delivery rate, multiple events are coalesced into one touch event whose location reflects the most recent touch. However, the additional touch information is available for apps that need more precision." Not ProMotion, but a welcome promotion to the good ol' touch layer nonetheless, and a good compromise between performance and power draw.

source: Apple

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