outputtriangle.cpp

#include <iostream>
#include <cmath>
using namespace std;

void outputTriangle(double x1, double y1, double z1,
		    double x2, double y2, double z2,
		    double x3, double y3, double z3,
		    double scale,
		    double xcenter, double ycenter,
		    double zcenter) {

  double u1=x2-x1, v1=y2-y1, w1=z2-z1,
    u2=x3-x1, v2=y3-y1, w2=z3-z1;
  
  // vertices are ordered counterclockwise
  double n1 = v1*w2-v2*w1, n2= w1*u2-w2*u1, n3 = u1*v2-v1*u2;
  double norm=sqrt(n1*n1+n2*n2+n3*n3);
  n1=n1/norm; n2=n2/norm; n3=n3/norm;

  x1 = (x1-xcenter)*scale;
  x2 = (x2-xcenter)*scale;
  x3 = (x3-xcenter)*scale;

  y1 = (y1-ycenter)*scale;
  y2 = (y2-ycenter)*scale;
  y3 = (y3-ycenter)*scale;

  z1 = (z1-zcenter)*scale;
  z2 = (z2-zcenter)*scale;
  z3 = (z3-zcenter)*scale;

  cout << "facet normal "
       << n1 << " " << n3 << " " << -n2 << endl
       << "    outer loop" << endl
       << "        vertex " << x1 << " " << z1 << " " << -y1 << endl
       << "        vertex " << x2 << " " << z2 << " " << -y2 << endl
       << "        vertex " << x3 << " " << z3 << " " << -y3 << endl
       << "    endloop" << endl
       << "endfacet" << endl;

}