SHADERS

Notes from Renderman Shaders:

- Types of shaders:

  - light shaders: calculates the color of light emitted from a point on 
    the surface of the light.

      - color (spectrum)
      - intensity
      - direction
      - falloff

  - surface shaders: based on incoming illumination and material properties,
    these determine the color reflected from a surface.

  - volume shaders: modify light ray as it travels through a medium or volume.

  - displacement shaders: alter surface point (along normal)

  - transformation shaders: non-linear xforms of points; camera projections

  - image shaders (aka imagers): final pixel operations

- Context:

  - surface shader
  - exterior volume shader (atmosphere)
    - attenuates light influence
  - interior volume shader 
  - light sources
    - lights can be attached to prims to create area light sources
  - xform (linear, non-linear)
  - displacement shader
  - imager

- Built in shaders:

  - Light Shaders

    - ambientlight
    - distantlight
    - pointlight
    - spotlight

  - Surface Shaders 

    - constant
    - matte
    - metal
    - shinymetal
    - plastic
    - paintedplastic

  - Atmosphere

    - fog
    - depthcue

  - Displacement

    - bumpy

- uniform vs varying parameters
  - for specifying at vertices and interpolated across surface

  - predefined set of varying parameters for each shader
    we would set these as attribs in python shader objects before invoking
    its shade() method

- I is NOT normalized on entry to shaders. It is the distance b/w ray origin
  and P.

- faceforward() ?
  opposite() ?

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