Extensions are a means to extend maxwell capabilities in several areas: geometry loaders, geometry modifiers, procedural geometry, scene modifiers and procedural textures.
Geometry loaders allow geometry to be loaded at the beginning of the render process. It's an external referencing mechanism that substantially decreases the size of .mxs files. Proxy objects and external referencing can be implemented using these extensions.
Geometry modifiers allow an object to be modified at the beginning of the render process. For example, a coarse geometry object could be refined just before starting the render, depending on some scene setup.
Procedural geometry extensions enable maxwell to render mathematically defined primitives. It is geometry created on-the-fly. Given a ray, with origin and direction, their main task is to calculate an intersection point and a surface normal. In addition to this, given an intersection point these extensions can also calculate UV coordinates, used mainly for texturing purposes. An extension can define an arbitrary number of ways of generating these coordinates.
Scene modifiers are able to change elements in the scene just before the render starts.
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