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Shader Basics

A shader is a miniature computer program that controls the behavior of the mental ray® rendering software during, or immediately after (in the case of output shaders), the rendering process. Some shaders are invoked by mental ray to compute the color values of pixels. Other shaders can displace or create geometry on the fly.

There are many different types of shaders: surface, environment, volume, shadow, photon, light, lens, texture, and so on. Each of these types of shaders are described in The Shader Library.

Networks of connected shaders can be packaged together as presets that create a single, complex visual effect. A preset contains a structure of individual elements—or nodes—called a render tree (which is a type of DAG—directed acyclic graph). Each node on these trees corresponds to a single shader.

In addition to mental ray shaders, SOFTIMAGE |XSI also has a library of realtime shaders. Instead of controlling the mental ray renderer, the realtime shaders control the realtime rendering pipeline. For information about realtime shaders, see the Realtime Shaders guide.

Every object is defined by its material. A material shader acts as a placeholder and accepts different types of shaders to define a material an object’s look. All aspects of the shader are automatically integrated into the scene; you do not have to worry about which shaders are dependent on others.

Shader Inputs and Outputs

To create customized or detailed effects, you have to know how to connect shaders to one another, whether you are working in the render tree or simply mapping shaders together via their connection icons. For information about shader input and outputs, see Shader Inputs and Outputs.

MetaShaders

MetaShaders are multi-implementation shaders that can support several renderers simultaneously. Many of the shaders in XSI’s shader library are MetaShaders, supporting both XSI’s built-in mental ray renderer and Cg renderers.

For information about how to recognize MetaShaders in the render tree, see MetaShaders in the Render Tree.

For information about creating your own MetaShaders, see Help > SDK Guides > SDK Customization Guide > MetaShaders.

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