surface
swap_trace(float swap = 0,
				 ri = 0.5;
		   color surfcolor = (1,1,1))
{
vector  i = normalize(I);
normal  n = normalize(N),
        nf = faceforward(n, i);
color   reflectioncolor = 0;


Ci = Cs;


Oi = Os;

if (swap == 0)
{
	if(nf.-i > 0)
    {
    vector reflectDirection = reflect(i, nf);
    reflectioncolor += trace(P, reflectDirection);
    }
}else{

	if(nf.-i > 0)
    {
    vector reflectDirection = refract(I, nf, ri);
    reflectioncolor += trace(P, reflectDirection);
    }
}	

 Ci = Os * surfcolor * reflectioncolor;
}