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From Odwiki

In mantra and RenderMan complient renderers, atmosphere shaders are used to globally modulate the results of SurfaceShader execution.

On entry to the atmosphere shader, the Cf/Ci and Of/Oi variables are initialized with the results of the surface shader. The atmosphere shader can modify these values in any way it chooses.

A simple depth-cue atmosphere shader (written in VEX) might look something like:

atmosphere
depthcue(float near=.1, far=100)
{
    Cf *= smooth(near, far, P.z);
}

Of course, an atmosphere shader doesn't have to simulate fog effects, it can modify the Cf variable in any way it chooses. For example:

atmosphere
negative()
{
    Cf = 1-Cf;
}

See Also

• Rendering
• MantraShaders