This repository contains an iOS project written in Swift 3.0 where I've tried to recreate a parallel prefix sum algorithm written in Metal for educational purposes and then compare against validity and performance of the MPSImageIntegral class provided by Apple. Given a first attempt it's not even that bad (around ~70 FPS on a 720p image with my implementation as compared to ~260 FPS with MPSImageIntegral on a iPhone 6S). I've tried to optimize if by fixing the algorithm to a specific block size, unrolling all loops and using float4 values in each thread in order to save global memory bandwith.
The TestClassfile gives an idea on how to use the IntegralImage class. It's basically instantiating the class via
IntegralImage(device: MTLDevice, library: MTLLibrary, width: Int, height: Int, inclusive: Bool)
where inclusive indicates whether the computed sums at (x,y) should include I(x,y).
Feel free to experiment and check out the source. The repository is not maintained and I don't guarantee validity (even though all tests are passing just fine).