Mappable parameters are parameters that can be connected to weight maps, texture maps, and UV properties. The purpose of mapping is to modulate the effect that a parameter has using the values of the map. For example, you can decide where and how long the hairs on a character will be using a weight map.
All mappable parameters are identified in their property editors with a connection icon.
Mappable parameters are discussed fully in Parameter Maps. The process for using mappable parameters for hair is a little different than other objects, so there are separate procedures for connecting maps to hair.
You can apply a weight map to any mappable hair parameter except for parameters in the Hair Shading and Hair Gradient Material shaders (which accept only texture maps).
For a basic procedure of connecting a weight map to hair, see Connecting Maps to Render Hair Parameters.
A texture map is the combination of a texture projection and an image. It has most of the attributes of a texture (including the projection parameters) but it cannot be rendered. To create a texture map, you select the texture projection method, then link an image file to it. The combination creates the specific texture map.
Instead of one value being applied over the surface as with a weight map, a texture map applies a color. A texture map works by averaging the RGB values in the image file to come up with a value between 0 and 1. Any value over 0 has an effect on the connected parameter. The greater the contrast in the image, the more pronounced the effect on the connected parameter.
You can apply a texture map to mappable parameters for the hair object and the Hair Shading and Hair Gradient Material shaders.
For a basic procedure of connecting a texture map to hair, see Connecting Maps to Render Hair Parameters.
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