Abstract This 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.

Abstract In 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 preceding 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 for mesh 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.

Abstract In this paper, we show how recent GPUs can be used to very efficiently and conveniently sample the visibility between two surfaces, given a set of occluding triangles. We use bitwise arithmetics to evaluate, encode, and combine the samples blocked by each triangle. In particular, the number of operations is almost independent of the number of samples. Our method requires no CPU/GPU transfers, is fully implemented as geometric, vertex and fragment shaders, and thus does not impose to modify the way the geometry is sent to the graphics card. We finally present applications to soft shadows, and visibility analysis for level design.

This paper presents a novel approach that uses graphics hardware to dynamically calculate a voxel-based representation of a scene. The voxelization is obtained on run-time in the order of milliseconds, even for complex and dynamic scenes containing more than 1,000,000 polygons. The voxelization is created and stored on the GPU avoiding unnecessary data transfer. The approach can handle both regular grids and locally optimized grids that better fit the scene geometry. The paper demonstrates applications to shadow calculation, refraction simultation and shadow volume culling/clamping.

International audience

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We introduce billboard clouds -- a new approach for extreme simplification in the context of real-time rendering. 3D models are simplified onto a set of planes with texture and transparency maps. We present an optimization approach to build a billboard cloud given a geometric error threshold. After computing an appropriate density function in plane space, a greedy approach is used to select suitable representative planes. A good surface approximation is ensured by favoring planes that are "nearly tangent" to the model. This method does not require connectivity information, but instead avoids cracks by projecting primitives onto multiple planes when needed. For extreme simplification, our approach combines the strengths of mesh decimation and image-based impostors. We demonstrate our technique on a large class of models, including smooth manifolds and composite objects.

Visibility determination is a key requirement in a wide range of graphics algorithms. This paper introduces a new approach to the computation of volume visibility, the detection of occluded portions of space as seen from a given region. The method is conservative and classifies regions as occluded only when they are guaranteed to be invisible. It operates on a discrete representation of space and uses the opaque interior of objects as occluders. This choice of occluders facilitates their extension into adjacent opaque regions of space, in essence maximizing their size and impact. Our method efficiently detects and represents the regions of space hidden by such occluders. It is the first one to use the property that occluders can also be extended into empty space provided this space is itself occluded from the viewing volume. This proves extremely effective for computing the occlusion by a set of occluders, effectively realizing occluder fusion. An auxiliary data structure represents occlusion in the scene and can then be queried to answer volume visibility questions. We demonstrate the applicability to visibility preprocessing for real-time walkthroughs and to shadow-ray acceleration for extended light sources in ray tracing, with significant acceleration in both cases.

This paper describes the successful combination of pre‐generated and dynamically updated image‐based representations to accelerate the visualization of complex virtual environments. We introduce a new type of impostor, which has the desirable property of limiting de‐occlusion errors to a user‐specified amount. This impostor, composed of multiple layers of textured meshes, replaces the distant geometry and is much faster to draw. It captures the relevant depth complexity in the model without resorting to a complete sampling of the scene. We show that layers can be dynamically updated during visualization. This guarantees bounded scene complexity in each frame and also exploits temporal coherence to improve image quality when possible. We demonstrate the strengths of this approach in the context of city walkthroughs.