/* basic swap texture shader.  Allows the user to define and swap textures between */
/* the inside and outside of an object */

surface
tex_swap(float	Kd = 1,			 /* basic brightness */
		 		swap = 0; 		 /* allows for swapping texture in parameters */
		 string inside_map = "", /* inside texture map */
		 		outside_map = "" /* outside texture map */)
{
color	surfcolor = texture(outside_map); /* defines the default surface texture */

/* make a copy of the surface normal one unit in length */
normal	n = normalize(N);
normal	nf = faceforward(n, I);

/* set the apparent surface opacity */
Oi = Os;

/* this IF statement defines which texture the shader needs to apply to what surface */
/* when the swap parameter is set at 0 */
if (swap == 0)
{
	if(n == nf)
		surfcolor = texture(inside_map);

/* if the swap parameter is not 0, then it applies the textures to the opposite surfaces */
		
}else {
	surfcolor = texture(inside_map);	
	if(n == nf)
		surfcolor = texture(outside_map);
}

/* calculate the diffuse lighting component */
color	diffusecolor = Kd * diffuse(nf);




/* calculate the apparent surface color */
Ci = Oi * Cs * surfcolor * diffusecolor;
}