odd_even.cc
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	// Odd/even face coloring code
	//
	// Author : Chris H. Rycroft (LBL / UC Berkeley)
	// Email : chr@alum.mit.edu
	// Date : August 30th 2011

	#include <vector>
	using namespace std;

	#include "voro++.hh"
	using namespace voro;

	// This function returns a random floating point number between 0 and 1
	double rnd() {return double(rand())/RAND_MAX;}

	int main() {
	unsigned int i;
	double x,y,z,rsq,r;
	voronoicell v;

	// Initialize the Voronoi cell to be a cube of side length 2, centered
	// on the origin
	v.init(-1,1,-1,1,-1,1);

	// Cut the cell by 250 random planes which are all a distance 1 away
	// from the origin, to make an approximation to a sphere
	for(i=0;i<250;i++) {
	x=2*rnd()-1;
	y=2*rnd()-1;
	z=2*rnd()-1;
	rsq=xx+yy+z*z;
	if(rsq>0.01&&rsq<1) {
	r=1/sqrt(rsq);x=r;y=r;z*=r;
	v.plane(x,y,z,1);
	}
	}

	// Calculate the orders of the faces and the normal vectors
	vector<int> f_vert;
	vector<double> nor;
	v.face_orders(f_vert);
	v.normals(nor);

	// Output POV-Ray planes with textures based on whether a face is
	// composed of an odd or even number of edges
	const char* parity[2]={"even","odd"};
	FILE *fp=safe_fopen("odd_even_pl.pov","w");
	for(i=0;i<f_vert.size();i++)
	fprintf(fp,"plane{<%g,%g,%g>,0.5 texture{t_%s}}\n"
	,nor[3i],nor[3i+1],nor[3*i+2]
	,parity[f_vert[i]&1]);
	fclose(fp);

	// Save the Voronoi cell as a spheres and cylinders
	v.draw_pov(0,0,0,"odd_even_v.pov");
	}