INTERFACE PGM;

IMPORT Rd, Wr;

TYPE
  T = RECORD
      nx, ny: CARDINAL;
      dxdy: CARDINAL;
      maxval: [0..255];
      v: REF ARRAY OF ARRAY OF CARDINAL
    END;

PROCEDURE New(nx, ny: CARDINAL; dxdy: CARDINAL := 0; maxval: CARDINAL := 255): T;
  (*
    Allocates a new texture, with given dimensions 
    and all zero pixels. *)

PROCEDURE Read(rd: Rd.T): T;
  (*
    Reads a texture from the given stream, assumed to be
    in "PGM" file format, either binary (P5) or ascii (P2). 
    
    The "dxdy" parameter is set to 0. *)

PROCEDURE Write(wr: Wr.T; READONLY t: T; binary: BOOLEAN := TRUE);
  (*
    Writes "t" to the given stream in the "PGM" file
    format; either binary (P5, default) or ascii (P2).
    
    The "dxdy" parameter is not written. *)

PROCEDURE PrintParms(wr: Wr.T; READONLY t: T);
  (* 
    Displays the dimensions and displacements of texture "t" 
    on the given writer. *)

PROCEDURE Reduce(READONLY t: T; VAR x, y, z: INTEGER);
  (*
    Given the grid coordinates of an arbitrary texel of the plane,
    returns the coordinates of an equivalent texel in the 
    fundamental region (the block [0..t.nx-1]x[0..t.ny-1]). *)

PROCEDURE Eval(READONLY t: T; x, y: REAL): CARDINAL;
  (* 
    Returns the value of texture "t" at point (x,y) of the plane,
    taking into account the periods and displacements of "t".
    
    Each texel is assumed to be a unit-side cube, and 
    the domain of texel [0,0] is assumed to be the 
    cube [0__1]^2.
  *)

END PGM.