Lazy visibility evaluation for exact soft shadows

International audienceThis report presents a novel approach to compute high quality and alias-free soft shadows using exact visibility computations. This work relies on a theoritical framework allowing to group lines according to the geometry they intersect. From this study, we derive a new algorithm encoding lazily the visibility from a polygon. Contrary to previous works on from-polygon visibility, our approach is very robust and straightforward to implement. We apply this algorithm to solve exactly and efficiently the visibility of an area light source from any point in a scene. As a consequence, results are not sensitive to noise, contrary to soft shadows methods based on area light source sampling. We demonstrate the reliability of our approach on different scenes and configurations

Application of Genetic Algorithm for Computing a Global 3D Scene Exploration

International audienceThis paper is dedicated to virtual world exploration techniques, which have to help a human being to understand a 3D scene. A new method to compute a global view of a scene is presented in the paper. The global view of a scene is determined by a “good” set off points of view. This method is based on a genetic algorithm. The “good” set of points of view is used to compute a camera path around the scene

Visibilité analytique dans l espace de Plücker (de la théorie aux applications pratiques)

Cette thèse aborde le problème du calcul analytique de la visibilité depuis un polygone, dans un contexte applicatif. Premièrement, nous mettons en évidence le fossé existant entre la théorie qui permet une élégante description du problème, et la pratique qui peine à proposer des implémentations robustes. Par la suite, nous nous appuyons sur le concept de classes d équivalence de droites orientées afin de proposer deux nouveaux algorithmes qui encodent l occlusion et la visibilité depuis un polygone dans l espace de Plücker. Les deux algorithmes utilisent cette information pour exploiter la cohérence visuelle qui existe entre des points voisins sur un même polygone et accélérer les calculs de visibilité depuis ces points. Contrairement aux méthodes existantes, notre approche est très robuste, et l information est encodée de manière paresseuse à l exécution. Les deux contextes applicatifs sont le calcul des ombres douces et de l occlusion ambiante en synthèse d images. Notre algorithme d occlusion distingue les droites occultées et non occultées. Il est utilisé pour calculer les fragments exacts d une source surfacique visibles depuis les points à ombrer. Notre algorithme de visibilité enrichit cette définition et regroupe de manière analytique les rayons issus d une surface selon les premiers objets intersectés. Les deux algorithmes obtiennent des résultats de haute qualité sans bruit ou autre artéfact, contrairement aux méthodes stochastiques ou basées sur une approximation de la visibilité. De plus, nos algorithmes sont compétitifs par rapport à une solution de production standard.This thesis addresses the from-polygon visibility problem in an applicative context. First of all, we underline the void which exists between the theory which allows an elegant description of this problem and the practice which struggles to provide efficient implementations. Then, we build on the theoretical concept of equivalence classes of oriented lines in order to propose two new algorithms which analytically encode from-polygon occlusion and from-polygon visibility in Plücker space. Both algorithms use this information to take advantage of the visual coherence which exists between neighbor points on the same polygon and speed up individual from-point queries. Contrary to previous methods, our approach is very robust, and the information is encoded lazily at run time, as directed by the visibility queries. The two applicative contexts are the generation of soft shadows and the calculation of ambient occlusion in image synthesis. Our from-polygon occlusion algorithmdistinguishes between occluded and unoccluded lines and it is used to calculate the exact fragments of a light source which are visible from the points to shade. Our from-polygon visibility algorithm improves this definition and analytically groups the view rays issued from a surface according to the first geometry they intersect. Both our algorithms achieve high quality results that are not sensitive to noise or other visual imperfections, contrary to other methods based on either sampling or visibility approximations. Moreover, our algorithms are competitive with respect to a standard production solution.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Analytic ambient occlusion using exact from-polygon visibility

International audienceThis paper presents a new method to compute exact from-polygon visibility, as well as a possible application to the calculation of high quality ambient occlusion. The starting point of this work is a theoretical framework which allows to group lines together according to the geometry they intersect. By applying this study in the context of from-polygon visibility, we derive an analytical definition which permits us to group the view rays according to the first geometry they encounter. Our new algorithm encodes lazily the visibility from a polygon. In contrast to the previous works on from-polygon visibility, our approach is very robust. For each point in the scene, the algorithm efficiently calculates the exact fragments of visible geometry. By combining this information with a analytical definition of ambient occlusion, we achieve results that are not sensitive to noise or other visual imperfections, contrary to ambient occlusion methods which are based either on sampling or visibility approximations