In the ProtoFlux FrooxEngineContext, a FieldDrive node is a listener node. Whenever the node is notified of a change from its input context, it will evaluate its input and write the result to the field. This makes ProtoFlux drives lazy by default—usually only evaluating their input when needed. However, as with all listener nodes, if the input node graph has a node marked with the ContinuouslyChanging property, it will cause the drive to evaluate its input every engine update.