#include "prototype.h"

/****** Function g_snell */

void g_snell(int *flag_R, double *x, double *y, double *angle_rad, double *phi_out, double *phi_prim,
	     double angle_rad_in, double phi_in, double n1, double n2, double r1, double r2)

  {
    
    double alpha;

    *flag_R = 1;
    *phi_prim = asin((n1/n2)*sin(phi_in));
    *phi_out = asin((r1/r2)*sin(phi_prim));

    if(*phi_out == 0)
      {
	if(r1 == r2)
	  alpha=PI-*phi_prim-*phi_out;
	else
	  alpha=*phi_out-*phi_prim;
      
	*angle_rad=angle_rad_in+alpha;

	*x=r2*cos(*angle_rad);
	*y=r2*sin(*angle_rad);

      }
    else
      {
	flag_R=0;
	*angle_rad=angle_rad_in;
	*x=r2*cos(*angle_rad_in);
	*y=r2*sin(*angle_rad-in);
      }

  }