Actions are objects that traverse a scene graph to drive some scene-related process.

One example is OpenGL rendering, and another one ray picking. At the most basic level, most action management will be done for the user behind the scenes in an SoSceneManager object, and the only actions one might need to get acquainted with are SoSearchAction and SoWriteAction.

For more advanced usage of Coin, one might want (or need) to take full control over driving all the actions oneself, in which case one will also need to know about the SoGLRenderAction, SoHandleEventAction, SoGetBoundingBoxAction, and SoRayPickAction.

The remaining actions are mostly more special-purpose actions of various kinds, except for the SoCallbackAction.

Before going to the step of implementing an extension action, one should really take a good look at the SoCallbackAction class, which is a general-purpose action that can be used as the framework for implementing almost any traversal-based process, with callback-hooks for all kinds of events that happen during traversal. In most cases, one can avoid the hassle of writing a new action, and just use SoCallbackAction instead.