This page demonstrates using custom variables in RSL, reading user attibutes from a RIB in the shader, and conditional evaluation.

The function demonstrated here is RSL's ability to read user attributes from a Maya scene, and for RIBs and RSL shaders utilize conditional evaluation. Also demonstrated, is the ability for RIB files to store and evaluate user variables

Application

Suppose in Maya we have a scene with a tree; each leaf is called leaf# and the trunk, or all other objects, are named something else. We would like to create a shader for the tree as a whole, that colors the leaves and the bark based on the name of the shape node.

Maya's RIB export

When Renderman Studio generates the RIB for render, names of objects show up as the following:

Attribute "identifier" "string name" ["leafShape197"]

RSL Development

There were three shaders developed.

1. uses a custom palette for each color
2. uses a base color, and variance in Hue, Saturation, and Value
3. applies colors to mimic new leaf growth.

Observation:

Note: I wasn't going for an accurate tree, or extensive shader, just a logical way of assigning colors.

Below is the basic color sample I used for my first two shaders

1. At first I decided a pallet of custom colors would provide good variety.

2. Custom palettes quickly become tedious, so the second shader was developed based on a primary color, then Hue, Saturation, Value variation.

3. Here you can see that the newer leaves at the maximum extent have a different color. My third Shader resembles this characteristic, loosly.

Development:

Shader 1 ---

here, each color is selected individually. I soon realised this method was faily cumbersome.

Shader 2 ---

here, a primary color, and HSV offsets are used.

Shader 3 ---

This shader shows the outside growth color around a radius:

More details on this shader to come...

Implementation

The shader is commented to explain how RSL can read and evaluate attributes

surface
wgsTreeHSV(float Kd = 1;
            string objectName = "leafShape";
            string alphaMap = "";
            color barkcolor     = color(0.4, 0.2, 0),
                  leafprimarycolor =  color(0.353,0.506,0.090);
            float lhd = 0.1, /*leaf hue delta [-0.5 0.5] */
                  lsd = 0.05, /*leaf sat delta [0.0] */
                  lvd = 0.1; /*leaf val delta [0.0] */
            )
{
/* --- Setup Variables --- */
color surfcolor = color(0.2,0.2,0.2);
normal n = normalize(N);
normal nf = faceforward(n, I);
uniform string shapename;
  
//color   surfcolorHSV = ctransform(  "hsv" ;  surfcolor);
//surfcolor = color(0.5,1,1);
  
//if poly has name attr, refer to it as shapename
if(attribute("identifier:name", shapename)) {
    //look for any micropolys with a name and number ;)
    string pattern = concat(objectName, "[0-9]*$");
    //if pattern exists in shapename,
    //it must be a poly that we want as a leaf:
    if(match(pattern, shapename)) {
        color lpc = ctransform("hsv",leafprimarycolor);
        //point diffp = point(lhd,lsd,lvd);
        color diffc = color(lhd,lsd,lvd);
        //color dcmax = color(1,1,1)-lpc;
  
    
        //apply aplha to all polys if we have one:
        if (alphaMap != "") 
            Oi = Os * float texture(alphaMap);
        else
            Oi = Os;            
        //Look at the trailing digit
        //if we have a "#" at end of poly:
             if(match("0$", shapename))
            //set color to lpc 
            surfcolor = ctransform("hsv","rgb",(  (lpc + diffc) ));
        else if(match("1$", shapename))
            surfcolor = ctransform("hsv","rgb",(  (lpc - diffc) ));
        else if(match("2$", shapename))
            surfcolor = ctransform("hsv","rgb",(  (lpc + diffc*0.5) ));
        else if(match("3$", shapename))
            surfcolor = ctransform("hsv","rgb",(  (lpc - diffc*0.5) ));
        else if(match("4$", shapename))
            surfcolor = ctransform("hsv","rgb",(  (lpc + 0) ));
        else
            surfcolor =leafprimarycolor;
      }
else {// colorize everything else differently
        surfcolor = barkcolor;
        Oi = Os; }
}
//Oi = Os;
color diffusecolor = Kd * diffuse(nf);
Ci = Oi * Cs * surfcolor * diffusecolor;
}

Additional Notes

RIB files themselves can also implement more advanced coding options. I will update this shortly...

Final Thoughts

Conidtional Eveluation enables limitless possibilities, so what I've demonstrated here is only one simple application. I would have liked to have spent more time developing the look of the shader, but the focus was just to implement conditionals. In that case, my goal was acheived.