Okay it looks like things have changed a bit, and a little reading of the original instructions at: https://developer.apple.com/documentation/scenekit/scnshadable#1654834 have cleared things up for me. In short, my float2 should be described as: #pragma arguments float2 worldDimensions; and after that the #pragma body #pragma transparent The shader now works fine again. Also, the SIMD files are presumably empty because they are deprecated in favor of just using the float2, float4 Metal types directly.

Well... it works if I split uniform float2 worldDimensions; into the more verbose uniform float worldX; uniform float worldY; Which is very annoying. Looking inside the <simd/simd.h> it looks empty? Like all these structs in <simd/vector_types.h> have been taken out??