Single Scattering Effects for Computer Games

International audienceThis paper addresses the rendering of single scattering effects such as glows and shafts of light, along with volumetric shadows induced by shadow casters in the participating media in real-time. Our method is easy to integrate in a video game graphics engine using the shadow volume technique since it requires only a little additional texture memory and is implemented with simple shaders. Realistic images can be produced in real-time for usual graphic scenes and at a high level framerate for complex scenes, allowing changes in the properties of participating medium, animations of objects and even light sources movements

Skeleton based importance sampling for path tracing

International audienceWhen working with large and complex scenes, situations arise where light flux takes complex paths to reach the observer. In such cases, traditional stochastic algorithms, like ray tracing algorithms, will have difficulties to compute noise-free images. Our present research aims to solve this problem using the 3d scene skeleton as a coarse representation. Indeed, curvilinear skeletons can be used to find light paths with higher energy. This article presents our research to use these skeletons for any ray tracing algorithm, allowing a knowledge-based choice when choosing light paths. Our method adds little computation time while producing a more accurate image

Practical morphological antialiasing on the GPU

International audienceThe subject of antialiasing techniques has been actively explored for the past 40 years. The classical approach involves computing the average of multiple samples for each final sample. Graphics hardware vendors implement various refinements of these algorithms. Computing multiple samples (MSAA) can be very costly depending on the complexity of the shading, or in the case of raytracing. Moreover, image-space techniques like deferred shading are incompatible with hardware implementation of MSAA since the lighting stage is decorrelated from the geometry stage. A filter based approach called Morphological Antialiasing (MLAA) was recently introduced [2009]. This technique does not need multiple samples and can efficiently be implemented on CPU using vector instructions. However, this filter is not linear and requires deep branching and image-wise knowledge which can be very inefficient on graphics hardware. We introduce an efficient adaptation of the MLAA algorithm running flawlessly on medium range GPUs

Autonomous Lighting Agents in Photon Mapping

proceedings of ISVC'05International audienceIn computer graphics, global illumination algorithms such as photon mapping require to gather large volumes of data which can be heavily redundant.We propose both a new characterization of useful data and a new optimization method for the photon mapping algorithm using structures borrowed from Artificial Intelligence such as autonomous agents. Our autonomous lighting agents efficiently gather large amounts of useful data and are used to make decisions during rendering. It induces less photons being cast and shorter rendering times in both photon casting and rendering phase of the photon mapping algorithm which leads to an important decrease of memory occupation and slightly shorter rendering times for equal image quality

A New Mathematical Development for Radiosity Animation with Galerkin

International audienceCombining animation and global illumination constitutes, at present, a true challenge in computer graphics, especially when light sources move in a complex scene because the entire illumination has to be recomputed. This paper introduces a new algorithm, based on the Galerkin method, which can efficiently manage any moving surface -even light source- to compute animation sequences. For each new frame of a sequence, we take into account the continuous property of the moves to determine the necessary energy differences between the previous global illumination solution and the new one. Based on a mathematical development of the form factor, this new approach leads to an efficient and simple algorithm, similar to the classical progressive refinement algorithm, and which computes animated sequence about three times faster

Real Time Rendering of Atmospheric Scattering and Volumetric Shadows

International audienceReal time rendering of atmospheric light scattering is one of the most difficult lighting effect to achieve in computer graphics. This paper presents a new real time method which renders these effects including volumetric shadows, which provides a great performance improvement over previous methods. Using an analytical expression of the light transport equation we are able to render directly the contribution of the participating medium on any surface. The rendering of shadow planes, sorted with a spatial coherence technique, and in the same philosophy than the shadow volume algorithm will add the volumetric shadows. Realistic images can be produced in real time for usual graphic scenes and at a high level framerate for complex scenes, allowing animation of lights, objects or even participating media. The method proposed in this paper use neither precomputation depending on light positions, nor texture memory

Autonomous lighting agents in global illumination

In computer graphics, physically-based global illumination algorithms such as photon-mapping have a linear progression between complexity and quality. To a given quality, rendering time scale linearly with computer performances. With Moore's law call in question and increasing demand in quality thoose algorithms need more and more optimisations. Existing optimisations such as irradiance caching are themselves very linear in performance gain. We propose a new optimisation method for the photon-mapping global illumination algorithm. We used structures borrowed from Artificial Intelligence such as autonomous agents to reduce computing time of the photon casting phase and rendering phase of the algorithm. Our structure called Autonomous Lighting Agents starts by using an agent-based scene discovery algorithm and is later used to make decisions during rendering inducing less photons beeing casted and smaller rendering times

Homeomorphic Alignment of Weighted Trees

International audienceMotion capture, a currently active research area, needs estimation of the pose of the subject. For this purpose, we match the tree representation of the skeleton of the 3D shape to a pre-specified tree model. Unfortunately, the tree representation can contain vertices that split limbs in multiple parts, which do not allow a good match by usual methods. To solve this problem, we propose a new alignment, taking into account the homeomorphism between trees, rather than the isomorphism, as in prior works. Then, we develop several computationally efficient algorithms for reaching real-time motion capture

Morphological Antialiasing and Topological Reconstruction

International audienceMorphological antialiasing is a post-processing approach which does note require additional samples computation. This algorithm acts as a non-linear filter, ill-suited to massively parallel hardware architectures. We redesigned the initial method using multiple passes with, in particular, a new approach to line length computation. We also introduce in the method the notion of topological reconstruction to correct the weaknesses of postprocessing antialiasing techniques. Our method runs as a pure post-process filter providing full-image antialiasing at high framerates, competing with traditional MSAA

Modeling and real-time rendering of participating media using the GPU

Cette thèse traite de la modélisation, l'illumination et le rendu temps-réel de milieux participants à l'aide du GPU. Dans une première partie, nous commençons par développer une méthode de rendu de nappes de brouillard hétérogènes pour des scènes en extérieur. Le brouillard est modélisé horizontalement dans une base 2D de fonctions de Haar ou de fonctions B-Spline linéaires ou quadratiques, dont les coefficients peuvent être chargés depuis une textit{fogmap}, soit une carte de densité en niveaux de gris. Afin de donner au brouillard son épaisseur verticale, celui-ci est doté d'un coefficient d'atténuation en fonction de l'altitude, utilisé pour paramétrer la rapidité avec laquelle la densité diminue avec la distance au milieu selon l'axe Y. Afin de préparer le rendu temps-réel, nous appliquons une transformée en ondelettes sur la carte de densité du brouillard, afin d'en extraire une approximation grossière (base de fonctions B-Spline) et une série de couches de détails (bases d'ondelettes B-Spline), classés par fréquence.%Les détails sont ainsi classés selon leur fréquence et, additionnées, permettent de retrouver la carte de densité d'origine. Chacune de ces bases de fonctions 2D s'apparente à une grille de coefficients. Lors du rendu sur GPU, chacune de ces grilles est traversée pas à pas, case par case, depuis l'observateur jusqu'à la plus proche surface solide. Grâce à notre séparation des différentes fréquences de détails lors des pré-calculs, nous pouvons optimiser le rendu en ne visualisant que les détails les plus contributifs visuellement en avortant notre parcours de grille à une distance variable selon la fréquence. Nous présentons ensuite d'autres travaux concernant ce même type de brouillard : l'utilisation de la transformée en ondelettes pour représenter sa densité via une grille non-uniforme, la génération automatique de cartes de densité et son animation à base de fractales, et enfin un début d'illumination temps-réel du brouillard en simple diffusion. Dans une seconde partie, nous nous intéressons à la modélisation, l'illumination en simple diffusion et au rendu temps-réel de fumée (sans simulation physique) sur GPU. Notre méthode s'inspire des Light Propagation Volumes (volume de propagation de lumière), une technique à l'origine uniquement destinée à la propagation de la lumière indirecte de manière complètement diffuse, après un premier rebond sur la géométrie. Nous l'adaptons pour l'éclairage direct, et l'illumination des surfaces et milieux participants en simple diffusion. Le milieu est fourni sous forme d'un ensemble de bases radiales (blobs), puis est transformé en un ensemble de voxels, ainsi que les surfaces solides, de manière à disposer d'une représentation commune. Par analogie aux LPV, nous introduisons un Occlusion Propagation Volume, dont nous nous servons, pour calculer l'intégrale de la densité optique entre chaque source et chaque autre cellule contenant soit un voxel du milieu, soit un voxel issu d'une surface. Cette étape est intégrée à la boucle de rendu, ce qui permet d'animer le milieu participant ainsi que les sources de lumière sans contrainte particulière. Nous simulons tous types d'ombres : dues au milieu ou aux surfaces, projetées sur le milieu ou les surfacesThis thesis deals with modeling, illuminating and rendering participating media in real-time using graphics hardware. In a first part, we begin by developing a method to render heterogeneous layers of fog for outdoor scenes. The medium is modeled horizontally using a 2D Haar or linear/quadratic B-Spline function basis, whose coefficients can be loaded from a fogmap, i.e. a grayscale density image. In order to give to the fog its vertical thickness, it is provided with a coefficient parameterizing the extinction of the density when the altitude to the fog increases. To prepare the rendering step, we apply a wavelet transform on the fog's density map, and extract a coarse approximation and a series of layers of details (B-Spline wavelet bases).These details are ordered according to their frequency and, when summed back together, can reconstitute the original density map. Each of these 2D function basis can be viewed as a grid of coefficients. At the rendering step on the GPU, each of these grids is traversed step by step, cell by cell, since the viewer's position to the nearest solid surface. Thanks to our separation of the different frequencies of details at the precomputations step, we can optimize the rendering by only visualizing details that contribute most to the final image and abort our grid traversal at a distance depending on the grid's frequency. We then present other works dealing with the same type of fog: the use of the wavelet transform to represent the fog's density in a non-uniform grid, the automatic generation of density maps and their animation based on Julia fractals, and finally a beginning of single-scattering illumination of the fog, where we are able to simulate shadows by the medium and the geometry. In a second time, we deal with modeling, illuminating and rendering full 3D single-scattering sampled media such as smoke (without physical simulation) on the GPU. Our method is inspired by light propagation volumes, a technique whose only purpose was, at the beginning, to propagate fully diffuse indirect lighting. We adapt it to direct lighting, and the illumination of both surfaces and participating media. The medium is provided under the form of a set of radial bases (blobs), and is then transformed into a set of voxels, together with solid surfaces, so that both entities can be manipulated more easily under a common form. By analogy to the LPV, we introduce an occlusion propagation volume, which we use to compute the integral of the optical density, between each source and each other cell containing a voxel either generated from the medium, or from a surface. This step is integrated into the rendering process, which allows to animate participating media and light sources without any further constraintPARIS-EST-Université (770839901) / SudocSudocFranceF