Relevant to Blender v2.31
As a final note on texture, let's look at the
fourth texture type button,
Blender allows the dynamic linking at run time of shared objects, both texture and sequence plugins. In both cases these objects are pieces of C code written according to a given standard (Chapter 27, Blender's Plugins System). In the case of texture plugins, these chunks of code define functions accepting coordinates as input and providing a Color, Normal and Intensity output, exactly as the procedural Textures do.
To use a Texture plugin, select this option, and then
Load Plugin button which appears in the
Texture Buttons. A neighboring window will turn into a File Select
window in which you can select a plugin. These plugins are
files on Windows and
.so files on various Unix
Once a plugin is loaded it turns the Texture Buttons window into its own set of buttons, as described in the individual plugin references.