A dynamic animation engine for generic spline objects

This paper introduces an accurate and efficient engine whose purpose is the dynamic animation of curvilinear objects which are modelled as successions of splines. At each time step the object shape conforms to its spline definitions, thus ensuring that each property implied by the chosen spline models is verified. This is achieved by animating spline control points. However, these control points are not considered as material points but rather as the degrees of freedom of the continuous object. The chosen dynamic equations (Lagrangian formalism) reflect this modelling scheme and yield an exact and very proficient linear system. In the chosen formalism, forces are introduced by either their potential energy or their power ratings in the virtual movements instilled by the degrees of freedom. Both methods are carried out in three cases: gravity, viscosity and generic force. Suitable and classical methods for constraint handling and numerical resolution are briefly discussed. Finally, this animation engine is applied to knitted patterns. Copyright 2000 John Wiley & Sons, Ltd.