ingo wrote:

> What are programmable shaders?
> Can sombody try explain this to me in laymens terms, or point me to a page
> that does so. I did a (very) quick search this morning but found only stuff
> that needs at least a basic understanding of shaders. And that I do not
> have.

Basically, shaders are functions written in the RenderMan Shading
Language
(a language that on first inspection looks very similar to C) that
explicitly describe the interaction between light and some element of
the scene being rendered. For instance, there are surface shaders (which
return the color of light reflected from a point on a surface),
displacement shaders (which allow the surface of a solid to be modified
in some algorithmic manner, such as regularly-spaced dimples or bumps),
volume shaders (which modify the characteristic of light passing through
a volume of space, the interior of an object, et cetera), and others.
Their power comes from the fact that shaders allow the artist to
describe
*exactly* how the light interacts with a surface, how light is generated
by a light source (light source shaders), how a surface interacts with
reflected light (by calculating intensity, direction, color of reflected
light), and so forth. The interaction need not even be realistic; you
have
total freedom in your calculations.

There is a rather significant learning curve involved in using shaders.
I'd recommend "The RenderMan Companion" by Steve Upstill as a start.
It's ten years old, but it's still considered the classic beginner's
text on RenderMan, and it gives a good overall view about what shaders
do.

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