Very bad performance for small UIViewControllerPreviewing.sourceRect

Number:rdar://35883989 Date Originated:December 6 2017, 11:50 AM
Status:Open Resolved:
Product:iOS + SDK Product Version:11.2
Classification:Performance Reproducible:Always

When UIViewControllerPreviewing.sourceRect is small popping previewing view controller is very slow.

It's a regression on iOS 11. It worked fine on iOS 10.

Steps to Reproduce:
1. Launch sample app on an iOS device that supports 3D Touch. If possible use an iPhone X because I feel this issue is more severe on iPhone X.
2. 3D touch the pink rectangle whose I deliberately set very small to make the issue more obvious.
3. Watch the slow peeking.



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