Mantra

Don't worry about the details given here. Important is at the moment only that there are several shader types. See Houdini's documentation:

$HH/vex/html/shading.html

• Displacement Shaders: Displacement shading can be used to move the position of the surface before the surface gets rendered. It is intended as a mechanism to add fine detail to a surface, not as a modelling technique.

• Fog Shaders: A fog shader is responsible for modifying the Cf, Of or Af variables after the surface shader has completed its shading. It is possible to use illuminance() statements inside of fog shaders.

• Image3D Shaders: Create 3D textures.

• Light Shaders will get called from surface or fog shaders to compute the illumination from a given light source. The light shader can be invoked using the illuminance() loop or using the standard diffuse(), specular(), etc. functions.

• Photon Shaders: When Mantra is generating photon maps, photon shaders are used instead of surface shaders. Thus, the photon context is very similar to the surface context. However, because of the behavioural differences between the contexts, most of the surface context specific functions are not valid in the photon context.

• Shadow Shaders: Shadow shaders will get called from surface or fog shaders to occlude the illumination from a given light source. The light will already have been computed by calling the light shader. The function of a shadow shader is to modify the Cl variable. Typically, the light will be occluded, causing the Cl variable to decrease in intensity. However, it is possible to create "negative" shadows, and increase the illumination due to occlusion.

• Surface Shaders: The surface shading context's purpose is to set the final color, opacity and alpha of the surface being rendered. If the Of and Af variables are not set, they will default to 1. If the Af variable is not set, it will resolve to avg(Of). It is possible to set the Af variable to any arbitrary value, making it possible to build matte/cutout shaders.

For help about Houdini or Mantra please visit the following web site where you can find tutorials and discussion forums:

http://www.sidefx.com/community