Specifying algorithm visualizations: Interesting events or state mapping?

Perhaps the most popular approach to animating algorithms consists of identifying interesting events in the implementation code, corresponding to relevant actions in the underlying algorithm, and turning them into graphical events by inserting calls to suitable visualization routines. Another natural approach conceives algorithm animation as a graphical interpretation of the state of the computation of a program, letting graphical objects in a visualization depend on a program's variables. In this paper we provide the first direct comparison of these two approaches, identifying scenarios where one might be preferable to the other. The discussion is based on examples realized with L the systems Polka and Leonardo