Project : evasion
Section: New Results
Procedural methods for geometry and motion
A generic tool for multi-resolution procedural modelling
Procedural modelling is probably the only approach enabling the modelling of a virtually infinite world with an unlimited number of details of different scales, that may be auto-similar or not. The last part of Frank Perbet's thesis, which will be defended in February 2004, proposes a generic tool, based on dynamic graphs, for exploring this kind of model very efficiently. Only the parts of the scene which are currently visible are generated, at the adequate level of details, enabling real-time display even during interactive zooming operations .
Procedural Textures based on Patterns
We developed a representation for virtually very large textures, which are especially useful is the case of natural scenes since the field of view is very large and at the same time the first stage requires a very high resolution. The principle consists in starting with a set of samples, then to describe how to spread and combine them in texture space: non-periodic tiling, Poisson-disk distribution, probability distribution, control of the spatial spreading, etc... (see figure 6). This model draws on the new means offered by the current graphics board revolution. A fragment program (or shader) running on the graphics board determines for each pixel with given texture coordinates which colour (or transparency, or normal...) to apply depending of the specifications. This work has been published at the ACM Symposium on Interactive 3D Graphics'03 .
This allows to encode a large part of an object's aspect in texture space, without modifying the geometry (refinement can then be controlled exclusively by independent criteria). We started to apply this approach to the volumetric textures representation previously developed in the team. Moreover, our model also deals with animation.
Procedural geometric skinning
Adding details to an animation while avoiding the heavy coast of a physically-based simulation can be done through a procedural approach. We just proposed a method of that kind for generating skin and cloth wrinkles on top of a standard character animation  : the dynamic wrinkles layer uses the deformations of the underlying mesh together with constraints such as length preservation for generating local deformations mimicking wrinkles. Results are generated in real-time.
Interactive procedural animation
We address the issue of interactively animating large complex vegetal scenes such as a meadow with trees and characters acting on the vegetation (see figure 7). We build on our previous model which consists of three levels of detail (LODs): 3D vegetation in the foreground, semi-transparent textures on deformable polygons in the middle, and ground texture for the background. We improve on our previous approaches by reducing several artefacts due to LODs and allowing the characters to tread the grass. The terrain is seen as a continuous noised function sampled at mesh nodes. Walking characters generate a potential stored in terrain nodes. This potential is combined with other parameters (shape, height, density, etc.) to render the grass. The potential eventually vanishes to simulate a progressive shape recovery .