#include "geom_tin.h"


///////////////////////////////////////////////////////////////////////////////
// determinant - computes the determinant of a 2x2 matrix
//
long determinant(COORD a, COORD b,COORD c,COORD d){
  return ((a*d) - (b*c));
}

///////////////////////////////////////////////////////////////////////////////
// interpolate - given and triangle and x,y; interpolate z
//
long interpolate(COORD* p1, COORD* p2, COORD* p3, COORD px, COORD py) {
  long d1 = determinant((p2[Y]-p1[Y]), (p2[Z]-p1[Z]), 
			  (p3[Y]-p1[Y]), (p3[Z]-p1[Z])); 
  long d2 = determinant((p2[X]-p1[X]), (p2[Z]-p1[Z]), 
			  (p3[X]-p1[X]), (p3[Z]-p1[Z])); 
  long d3 = determinant((p2[X]-p1[X]), (p2[Y]-p1[Y]), 
			  (p3[X]-p1[X]), (p3[Y]-p1[Y])); 
                                                                               
  /* d3 should never be 0 */                                                   
  if (d3 == 0){                                                                
    printf("determinant should never be 0\n");                                 
    exit(1);                                                                   
  }                                                                            
                                                                               
 return ((( ((py - p1[Y]) * d2) - ((px - p1[X]) * d1) ) / d3) + p1[Z]);       
                                                                               
}

///////////////////////////////////////////////////////////////////////////////
// findError - find the error of a given point in a triangle
//
long findError(int row,int col, int height, TRIANGLE* t) {
  long err = interpolate(t->p1,t->p2,t->p3, row, col);
  return  fabs((long)height-err);
}


/* /////////////////////////////////////////////////////////////////////////////// */
/* // determinant - computes the determinant of a 2x2 matrix */
/* // */
/* double determinant(COORD a, COORD b,COORD c,COORD d){ */
/*   return ((a*d) - (b*c)); */
/* } */

/* /////////////////////////////////////////////////////////////////////////////// */
/* // interpolate - given and triangle and x,y; interpolate z */
/* // */
/* double interpolate(COORD* p1, COORD* p2, COORD* p3, COORD px, COORD py) { */
/*   double d1 = determinant((p2[Y]-p1[Y]), (p2[Z]-p1[Z]),  */
/* 			  (p3[Y]-p1[Y]), (p3[Z]-p1[Z]));  */
/*   double d2 = determinant((p2[X]-p1[X]), (p2[Z]-p1[Z]),  */
/* 			  (p3[X]-p1[X]), (p3[Z]-p1[Z]));  */
/*   double d3 = determinant((p2[X]-p1[X]), (p2[Y]-p1[Y]),  */
/* 			  (p3[X]-p1[X]), (p3[Y]-p1[Y]));  */
                                                                               
/*   /\* d3 should never be 0 *\/                                                    */
/*   if (d3 == 0){                                                                 */
/*     printf("determinant should never be 0\n");                                  */
/*     exit(1);                                                                    */
/*   }                                                                             */
                                                                               
/*  return ((( ((py - p1[Y]) * d2) - ((px - p1[X]) * d1) ) / d3) + p1[Z]);        */
                                                                               
/* } */

/* /////////////////////////////////////////////////////////////////////////////// */
/* // findError - find the error of a given point in a triangle */
/* // */
/* double findError(int row,int col, int height, TRIANGLE* t) { */
/*   double err = interpolate(t->p1,t->p2,t->p3, row, col);     */
/*   return  fabs((double)height-err);                    */
/* } */