/* $Id: eval.c,v 1.2 1996/09/15 14:17:30 brianp Exp $ */

/*
 * Mesa 3-D graphics library
 * Version:  2.0
 * Copyright (C) 1995-1996  Brian Paul
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */


/*
 * $Log: eval.c,v $
 * Revision 1.2  1996/09/15 14:17:30  brianp
 * now use GLframebuffer and GLvisual
 *
 * Revision 1.1  1996/09/13 01:38:16  brianp
 * Initial revision
 *
 */


/*
 * eval.c was written by
 * Bernd Barsuhn (bdbarsuh@cip.informatik.uni-erlangen.de) and
 * Volker Weiss (vrweiss@cip.informatik.uni-erlangen.de).
 *
 * My original implementation of evaluators was simplistic and didn't
 * compute surface normal vectors properly.  Bernd and Volker applied
 * used more sophisticated methods to get better results.
 *
 * Thanks guys!
 */



#include <math.h>
#include <stdlib.h>
#include <string.h>
#include "context.h"
#include "draw.h"
#include "eval.h"
#include "dlist.h"
#include "macros.h"
#include "types.h"


/*
 * Tensor product Bezier surfaces
 *
 * Again the Horner scheme is used to compute a point on a 
 * TP Bezier surface. First a control polygon for a curve
 * on the surface in one parameter direction is computed,
 * then the point on the curve for the other parameter 
 * direction is evaluated.
 *
 * To store the curve control polygon additional storage
 * for max(uorder,vorder) points is needed in the 
 * control net cn.
 */

static void
horner_bezier_surf(GLfloat *cn, GLfloat *out, GLfloat u, GLfloat v,
                   GLuint dim, GLuint uorder, GLuint vorder)
{
  GLfloat *cp = cn + uorder*vorder*dim;
  GLuint i, uinc = vorder*dim;

  if(vorder > uorder)
  {
    if(uorder >= 2)
    { 
      GLfloat s, poweru;
      GLuint j, k, bincoeff;

      /* Compute the control polygon for the surface-curve in u-direction */
      for(j=0; j<vorder; j++)
      {
        GLfloat *ucp = &cn[j*dim];

        /* Each control point is the point for parameter u on a */ 
        /* curve defined by the control polygons in u-direction */
	bincoeff = uorder-1;
	s = 1.0-u;

	for(k=0; k<dim; k++)
	  cp[j*dim+k] = s*ucp[k] + bincoeff*u*ucp[uinc+k];

	for(i=2, ucp+=2*uinc, poweru=u*u; i<uorder; 
            i++, poweru*=u, ucp +=uinc)
	{
	  bincoeff *= uorder-i;
          bincoeff /= i;

	  for(k=0; k<dim; k++)
	    cp[j*dim+k] = s*cp[j*dim+k] + bincoeff*poweru*ucp[k];
	}
      }
        
      /* Evaluate curve point in v */
      horner_bezier_curve(cp, out, v, dim, vorder);
    }
    else /* uorder=1 -> cn defines a curve in v */
      horner_bezier_curve(cn, out, v, dim, vorder);
  }
  else /* vorder <= uorder */
  {
    if(vorder > 1)
    {
      GLuint i;

      /* Compute the control polygon for the surface-curve in u-direction */
      for(i=0; i<uorder; i++, cn += uinc)
      {
	/* For constant i all cn[i][j] (j=0..vorder) are located */
	/* on consecutive memory locations, so we can use        */
	/* horner_bezier_curve to compute the control points     */

	horner_bezier_curve(cn, &cp[i*dim], v, dim, vorder);
      }

      /* Evaluate curve point in u */
      horner_bezier_curve(cp, out, u, dim, uorder);
    }
    else  /* vorder=1 -> cn defines a curve in u */
      horner_bezier_curve(cn, out, u, dim, uorder);
  }
}