Smooth animation of algorithms in a declarative framework

Thanks to the increasing sophistication of modern workstations and display devices, supporting smoothly changing images has nowadays become a valuable feature in software visualization systems, but it seems difficult to achieve in declarative frameworks, as they are basically data (and not event) driven. This paper focuses on the problem of specifying animations of algorithms in a declarative style, addressing both automation and customization issues. We propose a general functional approach to animation modeling where animated behaviors of graphical objects are 'higher-order' attributes of the objects themselves expressed in the form of mathematical functions. These functions provide temporal and spatial information for creating smooth transitions between graphical scenes. The paper also describes the practical embodiment of our mathematical framework in the logic-based software visualization system Leonardo. Differently from previous approaches to smooth algorithm animation, detection of visual events and in-betweening scenes are completely automatic with our technique, Moreover, automation is supported without sacrificing customizability: default animated behaviors of graphical objects are automatically provided by the system, and practical solutions for specifying user-defined animation functions are supported as well. The quality of animations can be therefore incrementally improved by overriding the default behaviors as we show in some examples. (C) 2001 Academic Press.