Very good, this worked. Thanks very much! And it would seem that I need to do further reading about Swift, immutable and assignable. Cheers, thanks again

That is pretty interesting in a few different ways - And it compiles! Thanks so much for your response & solution, particularly in the WWDC aftermath ~ JL

Alignment really can cause issues when setting up buffers. Also, as was mentioned earlier, using a bridging header can give you a lot of control over the sizes of structs that Metal sees and that Swift can also write to. There is a great Swift sample project - https://github.com/MetalKit/metal/tree/master/raytracing from Marius Horga which explores one way to set up some triangle meshes. He recreates a project from Apple which was written in Objective C. Metal has really developed since then and you can do a phenomenal amount of path tracing with very few pipelines.

Very good, thanks so much! Will look through the Satin source code on GitHub.

I concur with the above request - MetalFX will be such an important framework going forward ( MTLFXTemporalScaler in particular ). The Boost performance with MetalFX Upscaling video was great, but there will still be some subtle choices to be made when setting up the textures. I've implemented MPSSVGFDenoiser ( following WWDC 2019 ) which has been incredibly useful, and I relied heavily on adapting the sample code. Thanks so much!

Fantastic, a sample project to explore... https://developer.apple.com/documentation/metalfx/applying_temporal_antialiasing_and_upscaling_using_metalfx ... Thanks!