I finally bit the bullet and installed iOS 9 Beta 2 on my iPad Air 2. This has allowed me to extend my OS X Metal Particles project with a new target: an iOS device!
The Swift ParticleLab class and the Metal shader code are shared between both targets - true cross platform coding!
Both my iPad Air 2 and my Macbook Pro (3 GHz Intel Core i7) manage about 30fps with four million particles on a 1024 x 768 texture - so performance is pretty much the across both devices. This may well changes as both iOS 9 and OS X 10.11 evolve - it will be interesting to see how the two classes of device evolve over the next few months.
After first installing iOS 9, I was unable to launch any Metal apps on my iPad with Xcode returning:
failed assertion _interposeHandle != NULL at /BuildRoot/Library/Caches/com.apple.xbs/Sources/Metal/Metal-54.7/Framework/MTLDevice.mm:110 MTLInitializeInterpose...this was rather worrying and I even created a Radar to report it. Luckily it was resolved by rebooting both my iPad and MBP - phew!
The new source code, which works under Xcode 7 Beta 2, is available at my GitHub repo here. I have heard the results are a bit ropey with some graphics chipsets - I'd love to hear your results.