Amazing Physically Based Rendering using the new iOS 10 SceneKit
Code for the following blog post
Requires Xcode 8, Swift 3, iOS 10, watchOS 3. Run on devices, not the simulator. Only devices support the Metal rendering API.
Sadly, the Apple Watch does not currently support Metal rendering. Hopefully Apple adds the capability for physical rendering in a future version of watchOS. H/T Stack Overflow question