Making grass and fur move

Abstract

This paper introduces physical laws into the real–time animation of fur and grass. The main idea to achieve this, is to combine shell-based rendering with a mass-spring system. In a preprocessing step, a volume array is filled with the structure of fur and grass by a method based on exponential functions. The volumetric data is used to generate a series of two dimensional, semitransparent textures that encode the presence of hair or of the blades. In order to render the fur volume in real–time, these shell textures are applied to a series of layers extruded above the initial surface. Moving fur can be achieved by horizontally displacing these shell layers at runtime through a mass–spring mesh. Four different mass–spring topologies – different arrangements of masses and springs over the grass–covered surface – are introduced and used for animation. Two of them allow the shell layers to separate laterally, so that the ”parting” of grass can be simulated. Performance observations prove mass-spring systems to be well-suited for the real–time simulation of fur and grass dynamics.