displacement_init Function

    type(displacement) function displacement_init(prim, func) result(out)
        !! Initialise the displacement modifier for a SDF.

        !> SDF to modify
        class(sdf_base), target :: prim
        !> Function to displace the SDF with.
        procedure(primitive) :: func

        out%func => func
        out%prim => prim

        out%optProps = prim%optProps

        out%layer = prim%layer
        out%transform = identity()

    end function displacement_init