Mental Ray

• Material Shaders are maybe the most important shader type in mental ray. They are called whenever a visible ray (eye ray, reflected ray, refracted ray, or transparency ray) hits an object.

• Volume Shaders may be attached to the camera or to a material. They accept an input color that they are expected to modify to account for the distance the ray travelled through a volume.

• Light Shaders are called from other shaders by sampling a light or directly if a ray hits a source.

• Shadow Shaders are called instead of material shaders when a shadow ray intersects with an object. Shadow rays are cast by light sources to determine visibility of an illuminated object.

• Environment Shaders provide a color for rays that leave the scene entirely, and for rays that would exceed the trace depth limit.

• Photon Shaders are used in the photon tracing phase to compute the photon maps that are used to simulate caustics and global illumination.

• Photon Volume Shaders are similar to photon shaders in the same way that volume shaders are similar to material shaders: they compute indirect light interactions in volumes, such as volume scattering.

• Photon Emitter Shaders are used in the photon tracing phase to control the emission of photons from the light sources.

• Texture Shaders are called exclusively by other shaders to relieve other shaders, such as material or environment shaders, from performing color and other computations.

• Displacement Shaders are called during tessellation of polygonal or free-form surface geometry. Whenever the tessellator introduces or copies a vertex, the displacement shader is called and expected to return a scalar value that tells the tessellator to move the vertex by this distance along its normal vector.

• Geometry Shaders are functions that procedurally create geometric objects. It allows mental ray to store small and simple placeholders in the scene, and generate the objects only when they are needed, and remove them from the cache when they are no longer needed.

• Contour Shaders compute contour colors and widths. Any information about the geometry, illumination, and materials of the scene can be used.

• Lens Shaders are called when a primary ray is cast by the camera. They may modify the eye ray's origin and direction to implement cameras other than the standard pinhole camera, and may modify the result of the primary ray to implement effects such as lens flares.

• Output Shaders are called when the entire scene has been completely rendered. They modify the resulting image or images to implement special filtering or compositing operations.

• Lightmap Shaders sample the object that the material is attached to, and compute a map that contains information about the object. This can be used to bake illumination solutions or store vertex colors for a hardware game engine.

The source code for a lot of mental ray shaders can be downloaded from mental images' FTP site:

ftp://ftp.mentalimages.com/pub/shaders/