GLOBALS

These are the texture coordinates for the surface at P.

These are the parametric values of the surface at P.

These values are the rate of change in the surface at P.

ncomps is the number of color components.
Default is 3: red green blue

This is the shutter time.

P is the position of the surface point.

N is the shading normal of the surface point.
N = dPdu ^ dPdv

I, the incidence vector, 
is where the camera vector intersects the surface point P.

L is the vector from the light source to P.

dPdu is the rate of change of the surface with respect to u.

dPdv is the rate of change of the surface point with respect to v.

Ng is the geometric normal of the surface point.
Ng = dPdu ^ dPdv

E is the camera postion.

Ps is the position of the surface point being shaded.

This is the new surface point, P returned to the renderer.
A new surface normal, N is also calculated.
These are the new globals used by any surface shader which follows.

The surface color which is set in the RIB stream.
The default is black.  Create a user defined color,
if you do not want that value used as the surface color.

The surface opacity which is set in the RIB stream.
The default is white.  Create a user defined float 
if you do not want that value used as the surface opacity.

This is the surface color returned to the Renderer.
It is the output of a Surface Shader.  The default is black.

This is the surface opacity returned to the Renderer.
It is the output of a Surface Shader.  The default is white.

This is the light color returned to the renderer.
It is the output of a Light Shader. The default is black.

This is the light opacity returned to the renderer.
It is the output of a Light Shader.  The default is white.

This is a user defined constant of any data type.
The output and input should be of the same data type.

This box makes it easy to use start/end/current frame values 
from a rib file, returning a value between 0 and 1. 
0 returns when current frame is start frame, 1 when it's end frame.
If the current frame is outside the start/end frame, values will
fall outside of the 0 to 1 range. This is not recommended, but possible.