/* William Schilthuis
	vsfx319 - Renderman
	Fire Shader - spring 2009
*/
surface wgs_fire01(
			float Kfb = 1;
            float rim_width = 0.15;
			color colr[7] ={color(0.945, 0.718, 0.439),
							color(1.000, 0.965, 0.596),
							color(1.000, 0.929, 0.561),
							color(1.000, 0.781, 0.220),
							color(1.000, 0.737, 0.365),
							color(0.831, 0.615, 0.431),
							color(0.529, 0.794, 0.937)};
			color opc[8] ={color(0.3),
							color(0.1),
							color(0.1),
							color(0.1),
							color(0.1),
							color(0.3),
							color(0.9),
							color(0.5)};
			float amp = 0.8;
			float freq = 9;
			float top = 0.1;
			float low = 0;
            )            
{
normal   n = normalize(N);
normal   nf = faceforward(n, I, n);
float    dist = 1 - t;
vector i = normalize(-I);
float  dot = i.nf;

float ns = noise(s*freq, t*freq);
float tt = t + ns * amp;

color    surfcolor = 1;

//"t" ramp for color //presented in tip to base order
color color_ramp = spline(dist, colr[0], colr[0], colr[1], colr[1], colr[2], colr[2],
								colr[3], colr[4], colr[5], colr[6], colr[6]);

surfcolor = color_ramp;

// ramp for opacity
color  displace = mix(top, low, tt);
color  opac_ramp = spline(dist, opc[0], opc[0], opc[1], opc[1], opc[2], opc[3],
								opc[3], opc[4], opc[5], opc[6], opc[7], opc[7]);

//"normal" ramp for opacity
Oi = ((smoothstep(rim_width, 1 , dot)) - (opac_ramp));
Ci = Oi * Cs * (surfcolor + opac_ramp) * Kfb;
}

			//notes//
// http://www.fundza.com/rman_shaders/flame/flame_color_ramps/index.html
// http://www.fundza.com/rman_shaders/surface/rim_effects/index.html 
// http://www.fundza.com/rman_shaders/smoothstep/index.html