/* basic blend texture shader.  Allows the user to define and blend textures between */
/* the inside and outside of an object */
surface
tex_blend(float	Kd = 1,	             /* basic brightness */
					blend = 1;       /* allows for blending texture in parameters */
		 	 string inside_map = "", /* inside texture map */
		 			outside_map = "" /* outside texture map */)
{
color	surfcolor, t1, t2; /* defines surface, t1, and t2 */

/* since textures can not be used in a MIX, the textures need to be redefined into varibles that can */
/* can be used within MIX */

t1 = texture(inside_map);
t2 = texture(outside_map);

/* 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;

/* defines the default for surface color */
surfcolor = mix(t1, t2, blend);

/* this If statement define how the shader needs to blends between the textures */
if(n == nf){
	surfcolor = mix(t2, t1, blend);
	}

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

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