This action defines a generic traversal of the scene graph. The user can specify callback functions for node types or paths; when those node types or paths are encountered during traversal, the user's callback function is called.

In addition, callback functions can be registered for primitives generated by shapes in the scene graph. Most shape types can generate primitives that represent or approximate their geometries. Triangle primitives are used for all surfaces (such as cubes, face sets, or 3D text), line segment primitives are used for line shapes, and point primitives are used for point shapes. Note that the type of primitives generated for a shape is the same, regardless of drawing style or other properties.

Most of the methods on this class access information from the traversal state. They should be called only by callback functions that are invoked during traversal, so there is a valid state to work with.