Recent advances in GPU technology have produced a shift in focus for real-time rendering applications, whereby improvements in image quality
Shadows, particularly soft shadows, play an important role in the visual perception of a scene by providing visual cues about the shape and position of objects. Several recent algorithms produce soft shadows at interactive rates, but they do not scale well with the number of polygons in the scene or only compute the outer penumbra. In this paper, we present a new algorithm for computing interactive soft shadows on the GPU. Our new approach provides both innerand outer-penumbra, and has a very small computational cost, giving interactive frame-rates for models with hundreds of thousands of polygons.Our technique is based on a sampled image of the occluders, as in shadow map techniques. These shadow samples are used in a novel manner, computing their effect on a second projective shadow texture using fragment programs. In essence, the fraction of the light source area hidden by each sample is accumulated at each texel position of this Soft Shadow Map. We include an extensive study of the approximations caused by our algorithm, as well as its computational costs. Key-words: Cartes d'ombres douces : calcul efficace de la visibilité de la source lumineuseRésumé : Les ombres, et en particulier les ombres douces, jouent un rôle important dans la perception d'une scène 3D. Elles fournissent des informations importantes sur la forme et la position des objets. De nombreuses recherches récentes ont montré comment produire des ombres douces en temps interactif, mais soit ces méthodes sont limitées soit dans les scènes qu'elles peuvent traiter, soit dans la qualité visuelle des résultats. Dans ce rapport, nous présentons un nouvel algorithme pour le calcul en temps-réel des ombres douces sur le GPU. Notre approche donne à la fois les pénombres intérieures et extérieures, consomme très peu de temps de calcul, ce qui lui permet des temps de rendu compatibles avec le temps réel pour des modèles de plusieurs centaines de milliers de polygones.Notre technique est basée sur une carte de profondeur des obstacles, comme pour la technique « shadow map ». Les pixels de cette carte de profondeur sont utilisés d'une façon nouvelle. Nous calculons leur contribution à une texture d'ombre douce en utilisant des fragment programs. La proportion de la source lumineuse qui est masquée par chaque échantillon est calculée, puis accumulée dans cette texture, la Soft Shadow Map. Nous présentons également une analyse détaillée des approximations introduites par notre algorithme, ainsi que des ses coûts de calcul.
The calculation of radiant energy balance in complex scenes has been made possible by hierarchical radiosity methods based on clustering mechanisms. Although clustering offers an elegant theoretical solution by reducing the asymptotic complexity of the algorithm, its practical use raises many difficulties, and may result in image artifacts or unexpected behavior. This paper proposes a detailed analysis of the expectations placed on clustering and compares the relative merits of existing, as well as newly introduced, clustering algorithms. This comparison starts from the precise definition of various clustering strategies based on a taxonomy of data structures and construction algorithms, and proceeds to an experimental study of the clustering behavior for real‐world scenes. Interestingly, we observe that for some scenes light is difficult to simulate even with clustering. Our results lead to a series of observations characterizing the adequacy of clustering methods for meeting such diverse goals as progressive solution improvement, efficient ray casting acceleration, and faithful representation of object density for approximate visibility calculations.
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