/*==========   	Celtic Braid Shader 	 	 ==========*/
/*==========   	  by Brandon Onstott		 ==========*/
/*==========   					 ==========*/
/*==========   	Uses ptlined() function to  	 ==========*/
/*==========   	create a three-strand repeatable ==========*/
/*==========   	braid.  Can switch between   	 ==========*/
/*==========   	cartesian and polar coordinates. ==========*/
/*==========   					 ==========*/
/*==========   	February 11, 1999	 	 ==========*/
/*==========   	VIZA 616 - Rendering and Shading ==========*/
/*==========   	Visualization Laboratory 	 ==========*/


#include "rmannotes.sl"

surface 
celtic_noise (	float	Ks		=  0.50, 
			Kd		=  0.50, 
			Ka		=  1.00, 
			roughness	=  0.10; 
		color 	specularcolor	=  1.00;
		float 	linewidth	=  0.10, 
			fuzz 		=  0.01, 
			freq 		= 10.00, 
			rmin 		=  0.20, 
			rmax 		=  0.45,
			rndm 		=  0.00,
			rdmf 		= 10.00,
			POLAR 		=  0.00 )
{
    normal 		Nf;
    vector		V;
    point		Ps, Psh;
    
    point l1a = point( 1.333, 0.8, 0);
    point l1b = point( 0.833, 0.2, 0);
    point l2a = point( 1.167, 0.2, 0);
    point l2b = point( 0.667, 0.8, 0);
    point l3a = point( 1.000, 0.8, 0);
    point l3b = point( 0.500, 0.2, 0);
    point l4a = point( 0.833, 0.2, 0);
    point l4b = point( 0.333, 0.8, 0);
    point l5a = point( 0.667, 0.8, 0);
    point l5b = point( 0.167, 0.2, 0);
    point l6a = point( 0.500, 0.2, 0);
    point l6b = point( 0.000, 0.8, 0);
    point l7a = point( 0.333, 0.8, 0);
    point l7b = point(-0.167, 0.2, 0);
    point l8a = point( 0.167, 0.2, 0);
    point l8b = point(-0.333, 0.8, 0);
    point l9a = point( 0.000, 0.8, 0);
    point l9b = point(-0.500, 0.2, 0);
    
    color 		surface_color, surface_opac, 
    			layer_color, layer_opac;
    color 		color1, color2, color3;
    float 		ss, tt, r, theta, rfreq;
    
    surface_color 	= color(0,0,0);
    surface_opac  	= 0.0;
    
    color1 		= Cs;
    color2 		= Cs * .66;
    color3 		= Cs * .33;

    Psh = transform("shader", P);
    ss = repeat(s, freq);
    tt = repeat(t, freq);
    
    /*============  POLAR COORDINATES  ===================*/
    
    if(POLAR == 1){
    
      rfreq = freq * 0.158333;
      ss = s-0.5;
      tt = t-0.5;

      topolar2d(ss, tt, r, theta);
    
      tt = (r - rmin) * (1.0/(rmax-rmin));
      ss = repeat(theta, rfreq);
    }
    
    /*====================================================*/
    Ps = point(ss,tt,0) + rndm*(0.5 - vector(noise(Psh*rdmf)));

/* LINE 1 */
    
    layer_color = color1;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l1a,l1b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 2 */
    
    layer_color = color2;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l2a,l2b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 3 */
    
    layer_color = color3;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l3a,l3b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 4 */
    
    layer_color = color1;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l4a,l4b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 5 */
    
    layer_color = color2;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l5a,l5b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 6 */
    
    layer_color = color3;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l6a,l6b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 7 */
    
    layer_color = color1;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l7a,l7b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 8 */
    
    layer_color = color2;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l8a,l8b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
/* LINE 9 */
    
    layer_color = color3;
    layer_opac  = 1.0 - smoothstep(linewidth, linewidth+fuzz, ptlined(l9a,l9b,Ps));

    surface_color = blend(surface_color, layer_color, layer_opac);
    surface_opac = union(surface_opac, layer_opac);
    
    Nf = faceforward( normalize(N), I );
    V = -normalize(I);

    Oi = surface_opac;
    Ci = Oi * ( surface_color * (Ka*ambient() + Kd*diffuse(Nf)) + 
	 	specularcolor * Ks * specular(Nf,V,roughness) );
}