Opal Shader

With the illuminance function we can get some interesting surface effects. In the examples below fractional brownian motion noise was applied to the surface point value; and the spline function was used to manipulate color and opacity.

Opal Version One

Opal Version Two

Version one uses color splines to manipulate surface color. The final version and other renditions were achieved by setting the opacity equal to the surface color and manipulating the color values for the color spline (see right).

View Code
View Final Rib Settings
Download .sl file

Images

Shader Applied to Maya Model

Detail of Picture to the Left

In the version above, the frequency of the opal is too high to look anything like a real opal. I want to be able to adjust this frequency in Maya, so have added in a variable to get the differing results below.

#include "H:/vsfx727/shaders/noise.h"
/* Shader description goes here */
surface
spline_test(float	Kd = 1,
	lucanarity = 1,
	gain = 1,
	detail = 1,
	freq = 1;
	color	c1 = color(1.0,0.4,0.0),
	c2 = color(1.0,1.0,0.0),
	c3 = color(1.0,0.6,1.0),
	c4 = color(1.0,1.0,0.8),
	c5 = color(0.4,0.0,0.4),
	c6 = color(1.0,0.4,0.0),
	c7 = color(1.0,1.0,0.0),
	c8 = color(1.0,0.6,1.0),
	c9 = color(1.0,1.0,0.8),
	c10 = color(0.4,0.0,0.4)
					)
{
normal	n = normalize(N);
normal	nf = faceforward(n, I);
color surfcolor = 1;
point p = transform(object,P);
 /*reset coordinate space*/
color c = color noise(P); 
/*effect color with surface point*/

/*manipulate the way light reacts to the surface*/
illuminance(P, nf, PI/2) {
	/*add the dot product of the Light ray an
d normal to the surface point*/
	p += nf.normalize(L);
	/*set phase01 to point p with applied
 fractional brownian motion (noise.h) */
	float phase01 = fbm(p,detail,lucanarity,gain);
	/* set phase02 to phase01 plus broken up light */
	float phase02 = phase01 + cellnoise(L) * .005;
	/* set surface color to a color spline value*/
	surfcolor = spline(phase02,c1,c1,c2,c3,c4,c5
,c6,c7,c8,c9,c10,c10);
	/* set the opacity equal to surface color */
	Oi = surfcolor;
}


/*Calculate the surface color*/
color	diffusecolor = Kd * diffuse(nf);
Ci = Oi * Cs * surfcolor * diffusecolor;
}

Final Rib Settings