(************************ ISOTROPIC INVARIANTS ***************************)

TYPE
  StateInvariants = ARRAY [0..State.N-1] OF RealInvariants;
  (*
    The five local isotropic invariants of order 2 at some texel
    of a texture.  See "ComputeInvariants" below for the formulas. *)

  RealInvariants = ARRAY [0..4] OF REAL;
  (*
    Isotropic invariants for one layer of the texture *)

PROCEDURE InvariantsFromDerivatives(
    READONLY v: RealDerivatives;
    VAR p: RealInvariants;
  );
  (*
    Computes the five isotropic order-2 local invariants
    "p[0..4]" from the spatial derivatives "v[0..5]", for 
    a single layer of a texture. *)
  
PROCEDURE StateInvariantsFromStateNeghborhood(
    READONLY n: StateNeighborhood;
    VAR p: StateInvariants;
  );
  (*
    Computes the local invariants at a  texel for all layers
    of the texture, given the neighborhood "n" of th texel. *)