Rendering Geometry with Relief Textures

International audienceWe propose to render geometry using an image based representation. Geometric information is encoded by a texture with depth and rendered by rasterizing the bounding box geometry. For each resulting fragment, a shader computes the intersection of the corresponding ray with the geometry using pre-computed information to accelerate the computation. Great care is taken to be artifact free even when zoomed in or at grazing angles. We integrate our algorithm with reverse perspective projection to represent a larger class of shapes. The extra texture requirement is small and the rendering cost is output sensitive so our representation can be used to model many parts of a 3D scene

Realistic Water Volumes in Real-Time

International audienceWe present a real-time technique to render realistic water volumes. Water volumes are represented as the space enclosed between a ground heightfield and an animable water surface heightfield. This representation allows the application of recent GPU-based heightfield rendering algorithms. Our method is a simplified raytracing approach which correctly handles reflections and refractions and allows us to render complex effects such as light absorption, refracted shadows and refracted caustics. It runs at high framerates by exploiting the power of the latest graphic cards, and could be used in real-time applications like video games, or interactive simulation

Fast Scene Voxelization Revisited

International audienceThis sketch paper presents an overview of ”Fast Scene Voxelization and Applications” published at the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games. It introduces slicemaps that correspond to a GPU friendly voxel representation of a scene. This voxelization is done at run-time in the order of milliseconds, even for complex and dynamic scenes containing more than 1M polygons. Creation and storage is performed on the graphics card avoiding unnecessary data transfer. Regular but also deformed grids are possible, in particular to better fit the scene geometry. Several applications are demonstrated: shadow calculation, refraction simulation and shadow volume culling/clamping

Occlusion Textures for Plausible Soft Shadows

International audienceThis paper presents a new approach to compute plausible soft shadows for complex dynamic scenes and rectangular light sources. We estimate the occlusion at each point of the scene using prefiltered occlusion textures, which dynamically approximate the scene geometry. The algorithm is fast and its performance independent of the light's size. Being image-based, it is mostly independent of the scene complexity and type. No a priori information is needed, and there is no caster/receiver separation. This makes the method appealing and easy to use

Street Generation for City Modelling

International audienceIn this paper, we present a complete solution for automatically retrieving the street graph of an urban model. Given a set of 2-5D polygons representing the buildings footprints and their heights, the algorithm constructs a graph that represent the street network (a node for a crossing, an edge a street, each associated with a set of surrounding buildings) along with geometric information such as the width of the streets. We demonstrate how this graph can be used to analyze the city structure and give an example of its use with an automatic geometric modeler for city streets

Erosion Based Visibility Preprocessing

International audienceThis paper presents a novel method for computing visibility in 2.5D environments. It is based on a novel theoretical result: the visibility from a region can be conservatively estimated by computing the visibility from a point using appropriately "shrunk" occluders and occludees. We show how approximated but yet conservative shrunk objects can efficiently be computed in a urban environment. The application of this theorem provides a tighter potentially visible set (PVS) than the original method it is built on. Finally, theoretical implications of the theorem are discussed, and we believe it can open new research directions

Pré-traitement de grosses bases de données pour la visualisation interactive

To navigate in real-time in a virtual environnement, one must be able to generate rapidly new views of the 3D model describing this environment. In this thesis, we got interested in pre-computing results that could later be used to speed-up the rendering of those views. Two directions have been explored. In a first part we pre-compute, for each possible location, a list of objects that are hidden by other objects and thus need not to be displayed. This pre-computation relies on a so-called "shrinking theorem": if from a view point a shrunk object is hidden by other objects which are also shrunk, then the object is certainly hidden from any neighbouring view point. The first contribution of this thesis is the demonstration of this theorem which formalizes and extends a previously known result. The second contribution is a robust algorithm to compute such shrinkings on any model, given it is watertight (with a well-defined exterior and interior). Once we have determined what is visible, we have to display it in the most efficient manner. A classical solution consists in having, for each object , different representations of different complexity. Depending on the distance between object ant the viewer, the most adequat simplification is displayed. The difficulty is then to build such level of details from an initial model. The third contribution of this thesis is a new representation, called billboard cloud which achieves extreme simplification while keeping a very good visual quality. A complex object is represented by a small number of textured polygons with transparency, whose interleaving allows to render both shape and appearance of the object. An automatic algorithm is described, to compute such a cloud from an initial polygonal model.Pour naviguer en temps réel dans un environnements virtuel, il faut être capable de fabriquer très rapidement des vues d'un modèle 3D décrivant cet environnement. Dans cette thèse nous nous intéressons à pré-calculer des résultats qui pourront être utilisés afin d'accélérer le rendu de ces images. Deux voies sont explorées. D'une part un pré-calcul de visibilité permet de déterminer, en chaque point de l'espace, une liste d'objets qui sont cachés par d'autres objets et n'ont donc pas besoin d'être affichés. Ce pré-calcul s'appuie sur un théorème dit " de réduction " : si en un point un objet réduit est caché par plusieurs objets eux-aussi réduits, alors au voisinage de ce point, l'objet est certainement caché. La première contribution de cette thèse est la démonstration de ce théorème qui formalise et généralise un résultat connu. La deuxième contribution est un algorithme robuste permettant de calculer de telles réductions pour un modèle quelconque, pourvu qu'il soit étanche (avec un extérieur et un intérieur bien définis). Une fois qu'est déterminé ce qui est visible, il reste à l'afficher de la manière la plus efficace possible. Une solution classique consiste à avoir pour chaque objet de l'environnement plusieurs représentations de plus en plus simplifiées. Selon la distance de l'objet à l'observateur, on affiche la simplification la mieux adaptée. La difficulté consiste alors à générer automatiquement ces différents niveaux de détails à partir du modèle initial. La troisième contribution de cette thèse est une nouvelle représentation, baptisée nuage de billboards, qui permet d'effectuer une simplification extrême tout en gardant une très bonne qualité visuelle. Un objet complexe est représenté par un petit nombre de polygones texturés avec de la transparence, dont l'enchevêtrement permet de restituer à la fois la forme et l'apparence de l'objet. Un algorithme complètement automatique permet de fabriquer un tel nuage à partir d'un modèle polygonal quelconque

N-Buffers for Efficient Depth Map Query

International audienceWe introduce the N-buffer as a tool for multiresolution depth map representation. This neighborhood buffer encodes the value and position of local depth extrema at different scales in an image cube, in contrast to the image pyramid. The resulting increase in storage space is largely compensated by the following benefits: objects of any size can be culled in constant time against an occlusion map using four depth lookups; visibility-like queries can be performed in vertex and fragment programs; N-buffers can be computed very efficiently with graphics hardware. We present three applications of this datastructure, and in particular a novel approach for shadow volume acceleration

On Exact Error Bounds for View-Dependent Simplification

Disponible : http://diglib.eg.org/EG/CGF/volume26/issue2/v26i2pp202-213.pdfInternational audienceIn this article we present an analytical closed-form expression to ensure exact error bounds for view-dependent simplification which is of importance for several algorithms. The present work contains proofs and solutions for the general 2D case and particular 3D cases. Most preceeding works rely on coarse heuristics, that might fail and/or restrict movements or object representations. We introduce the notion of validity regions as the complete set of possible simplifications respecting a given error bound between the object and its simplification. The approach handles arbitrary polygonal viewcells which allow for free movement in the interior. We show how to compute these regions foresh points and faces. Since the validity region of a face accounts for all its points, properties like silhouette preservation and textures are gracefully handled. This is not the case if the error is controlled only at the face's vertices or edges