MTLVertexStepFunction

The vertex function fetches attribute data once and uses that data for every vertex.

The vertex function fetches and uses new attribute data for every vertex.

The vertex function regularly fetches new attribute data for a number of instances that is determined by stepRate.

The post-tessellation vertex function fetches data based on the patch index of the patch.

The post-tessellation vertex function fetches data based on the control-point indices associated with the patch.