François Rousselle

Enhanced illumination of reconstructed dynamic environments using a real-time flame model

The goal of interactive walkthroughs in three dimensional computer reconstructions is to give people a sensation of immersion in different sites at different periods. Realism of these walkthroughs is achieved not only with detailed 3D models but also with a correct illumination regarding the means of lighting in those times. Working on the enhancement of the visual appearance of the computer reconstruction of the Gallo-Roman forum of Bavay, we propose a model that reproduces the shape, animation and illumination of simple flames produced by candles and oil lamps in real-time. Flame dynamics is simulated using a Navier-Stokes equation solver animating particle skeletons. Its shape is obtained using those particles as control points of a NURBS surface. The photometric distribution of a real flame is captured by a spectrophotometer and stored into a photometric solid. This one is used as a spherical texture in a pixel shader to compute accurately the illumination produced by the flame in any direction. Our model is compatible with existing shadow algorithms and designed to be easily incorporated in any cultural heritage real-time application.

Radiometric compensation for a low-cost immersive projection system

Catopsys is a low-cost projection system aiming at making mixed reality (virtual, augmented or diminished reality) affordable. It combines a videoprojector, a camera and a convex mirror and works in a non-specific room. This system displays an immersive environment by projecting an image onto the different parts of the room. However, the presence of an uncalibrated projector, heterogeneous materials and light inter-reflections influence the colors of the environment displayed in the room. Radiometric compensation of the projection process enables the system to reduce this problem. In this paper, we present our low-cost immersive projection system and propose a radiometric model and a compensation method which handle the projector response, surface materials and inter-reflections between surfaces. Our method works in two stages. First, the radiometric response of the projection process is evaluated. Then, this radiometric response is used to compensate the projection process in the desired environments.

Real-time animation of various flame shapes

Working on the computer reconstruction of the Gallo-Roman forum of Bavay, we try to improve the feeling of immersion in the virtual environment. One way to achieve this is to provide realistic and dynamic light sources. In this context, we need to model candles, oil lamps, torches or bonfires. We propose in this paper a model that can handle complex flames in real-time and manage interactivity. The fire is considered as a set of linear flames whose shapes are defined by the geometry of the combustible and the fuel distribution. Each individual flame is represented by a textured NURBS surface. Then, combining several real-time effects such as glow and true transparency, we are able to make the NURBS surfaces merge in a convincing way, and to give the impression of a real fire.

A progressive mesh method for physical simulations using lattice Boltzmann method on single-node multi-gpu architectures

In this paper, a new progressive mesh algorithm is introduced in order to perform fast physical simulations by the use of a lattice Boltzmann method (LBM) on a single-node multi-GPU architecture. This algorithm is able to mesh automatically the simulation domain according to the propagation of fluids. This method can also be useful in order to perform various types of simulations on complex geometries. The use of this algorithm combined with the massive parallelism of GPUs allows to obtain very good performance in comparison with the static mesh method used in literature. Several simulations are shown in order to evaluate the algorithm.

Real-time rendering and animation of plentiful flames

Rendering and animating flames in real time is a great challenge because of the complexity of the combustion process. While few models succeeded in simulating a single fire in real time, none tried to handle a large number of flames. In this paper we propose a set of techniques which aim at handling numerous flames like those of candles, torches or campfires in real time. We manage different levels of accuracy in the simulation, which is based on a fast fluid dynamics solver. We also consider many optimizations to reduce the rendering cost of a single flame. As a result, our approach is able to animate and render dozens of realistic flames in real-time, each one reacting independently to forces introduced at the scene level.

Hybridization techniques for fast radiosity solvers

The authors study, both theoretically and experimentally some properties of classical linear systems solvers, according to the radiosity assumptions. We prove important properties for some of these solvers which allow the user to choose the best one. We then introduce a new technique, so called hybridization, whose purpose is to increase the convergence speed of iterative methods. It provides very efficient results for the well-known Gauss-Seidel solver. This technique has been successfully applied to both a group progressive radiosity approach and a full-matrix radiosity method which has been specifically designed for plant growth simulation.

Path tracing using the AR350 processor

The AR350 is a ray tracing processor developed by Advanced Rendering Technologies. By using AR350 processors arrays, the PURE and RenderDrive products achieve high performances in Ray Tracing based rendering. In this paper we present an extension of their capabilities to global illumination computation by implementing Path Tracing based methods. Because the core program of these rendering appliances is not modifiable but driven by a Render-Man compliant interface, we achieve this goal by writing dedicated shaders. We obtain better indirect illumination than with the use of standard shaders and keep high performances by the exclusive use of the AR350 processors array for all intersection tests.

Group accelerated shooting methods for radiosity

The introduction of the Progressive Refinement method was the starting point of interactivity in the radiosity illumination process. Overshooting methods brought an important acceleration to the convergence particularly for scenes with a high mean reflectivity. In this paper we present a new acceleration technique to PR and overshooting methods based on group shooting methods. The acceleration is obtained by occasionally selecting groups of interacting patches and by solving the subsystem built from this group. This technique allows us to reduce the number of iterations that are required to solve the radiosity system and only involves a small computation overhead. Comparing different algorithms for scenes with particular properties, we highlight interesting results of the Group Accelerated Shooting Methods especially when considering complex scenes with many occlusions.

Fast massively parallel progressive radiosity on the MP-1

Radiosity is a powerful method for solving the global illumination problem in the case of purely diffuse light reflexions. The progressive refinement algorithm provides interactivity during computation by displaying intermediate images, and overshooting methods increases the convergence rate of progressive radiosity. However, computation times remain very important. Parallelising these algorithms is a good way to significantly improve interactivity by reducing computation time. The aim of this paper is to present a method for the parallelisation of the progressive refinement radiosity algorithm on a massively parallel SIMD machine. We took care of both the SIMD machine nature and the high number of available processors on studying the several ways to efficiently implement the algorithm. The parallel scheme we propose uses a disk projection area for form factors estimate and decreases dramatically the computation times.

Accelerating Physical Simulations from a Multicomponent Lattice Boltzmann Method on a Single-Node Multi-GPU Architecture

In this paper, we introduce an efficient method to accelerate flow simulations for an isothermal multiphase and multicomponent (MPMC) Lattice Boltzmann method (LBM) on a single-node multi-GPU architecture. Our objective is to propose an efficient way to improve performance of multiphase and multicomponent Lattice Boltzmann simulations by the use of Nvidia GPUDirect technology and Peer-to-Peer (P2P) data transfers. Optimization of Peer-to-Peer communications is also studied in this work by the use of a clustering algorithm. Several simulations are shown and performance is discussed in order to validate the method.