Controlled blending in contact situations

Interactive implicit modelling with complex skeletons was improved with the introduction of primitives defined at different LODs. These implicit primitives use a subdivision curve as a skeleton. In this paper an extension to this representation is presented, in order to make it suitable for the interactive modelling and animation of soft objects in contact situations. The first contribution improves the display method for subdivision-based implicit primitives; this uses an adaptive polygonisation which locally refines, where necessary, according to the currently selected LOD. The second contribution consists of a new method for preventing unwanted blending when a skeleton-curve folds back onto itself. The third introduces local deformations where surfaces that should not blend come into contact. We illustrate the benefits of this methodology by describing two applications: the interactive modelling of complex organic shapes in contact situations and the physically-based animation of such organic shapes.

1 Introduction

Although parametric surfaces have been more widely used, the blending properties of implicit surfaces make them particularly suited to organic modelling. In such cases soft and branching objects are more easily achieved thanwith their parametric counterparts. In particular, skeleton-based implicit surfaces generate a smooth coating along a skeleton, which can be animated. In this paper we focus on implicit surfaces generated by a graph of branching curves, following the methodology first introduced in [6]. The field function that generates the implicit surface is computed using convolution, which ensures bulge-free blending between implicit primitives at branching points. Moreover, the use of subdivision-curves as skeleton elemerts enables the generation of the implicit surface at different levels of detail (LODs), which makes this representation very convenient in an interactive modelling and animation framework. ^†

iMAGIS is a joint project of CNRS, INRIA, Institut National P olytechnique de Grenoble and Université Joseph Fourier.