Combining Higher-Order Wavelets and Discontinuity Meshing: a Compact Representation for Radiosity

Colloque avec actes et comité de lecture. internationale.International audienceThe radiosity method is used for global illumination simulation in diffuse scenes, or as an intermediate step in other methods. Radiosity computations using Higher-Order wavelets achieve a compact representation of the illumination on many parts of the scene, but are more expensive near discontinuities, such as shadow boundaries. Other methods use a mesh, based on the set of discontinuities of the illumination function. The complexity of this set of discontinuities has so far proven prohibitive for large scenes, mostly because of the difficulty to robustly manage a geometrically complex set of triangles. In this paper, we present a method for computing radiosity that uses higher-order wavelet functions as a basis, and introduces discontinuities only when they simplify the resulting mesh. The result is displayed directly, without post-processing

The Visibility Skeleton: A Powerful and Multi-Purpose Global Visibility Tool

International audienceMany problems in computer graphics and computer vision require accurate global visibility information. Previous approaches have typically been complicated to implement and numerically unstable, and often too expensive in storage or computation. The Visibility Skeleton is a new powerful utility which can efficiently and accurately answer visibility queries for the entire scene. The Visibility Skeleton is a multi-purpose tool, which can solve numerous different problems. A simple construction algorithm is presented which only requires the use of well known computer graphics algorithmic components such as ray-casting and line/plane intersections. We provide an exhaustive catalogue of visual events which completely encode all possible visibility changes of a polygonal scene into a graph structure. The nodes of the graph are extremal stabbing lines, and the arcs are critical line swaths. Our implementation demonstrates the construction of the Visibility Skeleton for scenes of over a thousand polygons. We also show its use to compute exact visible boundaries of a vertex with respect to any polygon in the scene, the computation of global or on-the-fly discontinuity meshes by considering any scene polygon as a source, as well as the extraction of the exact blocker list between any polygon pair. The algorithm is shown to be manageable for the scenes tested, both in storage and in computation time. To address the potential complexity problems for large scenes, on-demand or lazy contruction is presented, its implementation showing encouraging first results

High fidelity radiosity rendering at interactive rates

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 66-69).by Stephen Lincoln Hardt.M.Eng

Simplifying the Representation of Radiance from Multiple Emitters

International audienceIn recent work radiance function properties and discontinuity meshing have been used to construct high quality interpolants representing radiance. Such approaches do not consider the combined effect of multiple sources and thus perform unnecessary discontinuity meshing calculations and often construct interpolants with too fine subdivision. In this research we present an extended structured sampling algorithm that treats scenes with shadows and multiple sources. We then introduce an algorithm which simplifies the mesh based on the interaction of multiple sources. For unoccluded regions an a posteriori simplification technique is used. For regions in shadow, we first compute the maximal umbral/penumbral and penumbral/light boundaries. This construction facilitates the determination of whether full discontinuity meshing is required or whether it can be avoided due to the illumination from another source. An estimate of the error caused by potential simplification is used for this decision. Thus full discontinuitymesh calculation is only incurred in regions where it is necessary resulting in a more compact representation of radiance

The Virtual Mesh: A Geometric Abstraction for Efficiently Computing Radiosity

Article dans revue scientifique avec comité de lecture.International audienceIn this paper, we introduce a general-purpose method for computing radiosity on scenes made of parametric surfaces with arbitrary trimming curves. By contrast with past approaches that require a tessellation of the input surfaces (be it made up of triangles or patches with simple trimming curves) or some form of geometric approximation, our method takes fully advantage of the rich and compact mathematical representation of objects. At its core lies the \emph{virtual mesh}, an abstraction of the input geometry that allows complex shapes to be illuminated as if they were simple primitives. The virtual mesh is a collection of normalized square domains to which the input surfaces are mapped while preserving their energy properties. Radiosity values are then computed on these supports before being lifted back to the original surfaces. To demonstrate the power of our method, we describe a high-order wavelet radiosity implementation that uses the virtual mesh. Examples of objects and environments, designed for interactive applications or virtual reality, are presented. They prove that, by exactly integrating curved surfaces in the resolution process, the virtual mesh allows complex scenes to be rendered more quickly, more accurately and much more naturally than with previously known methods

Novel illumination algorithms for off-line and real-time rendering

This thesis presents new and efficient illumination algorithms for off-line and real-time rendering. The realistic rendering of arbitrary indirect illumination is a difficult task. Assuming ray optics model of light, the rendering equation describes the propagation of light in the scene with high accuracy. However, the computation is expensive, and thus even in off-line rendering, i.e., in prerendered animations, indirect illumination is often approximated as it would otherwise constitute a bottleneck in the production pipeline. Indirect illumination can be computed using Monte Carlo integration, but when restrained to a reasonable amount of computation time, the result is often corrupted by noise. This thesis includes a method that effectively reduces the noise by applying a spatially varying filter to the noisy illumination. For real-time performance, some components of indirect illumination can be precomputed. Irradiance volume and many variations of it precompute reflections and shadowing of a static scene into a volumetric data structure. This data is then used to shade dynamic objects in real-time. The practical usage of the method is limited due to aliasing artifacts. This thesis shows that with a suitable super-sampling approach, a significant quality improvement can be obtained. Another direction is to precompute how light propagates in the scene and use the precomputed data during run-time to solve both direct and indirect illumination based on the known incident lighting. To keep the memory and precomputation costs tractable, these methods are typically restricted to infinitely distant lighting. Those that are not, require a very long precomputation time. This thesis presents an algorithm that adopts a wavelet-based hierarchical finite element method for the precomputation. A significant performance improvement over the existing techniques is obtained. When full global illumination cannot be afforded, ambient occlusion is an attractive alternative. This thesis includes two methods for real-time rendering of ambient occlusion in dynamic scenes. The first method models the shadowing of ambient light between rigid moving bodies. The second method gives a data-oriented solution for rendering approximate ambient occlusion for animated characters in real-time. Both methods achieve unprecedented efficiency.reviewe

Master-element vector irradiance for large tessellated models

http://portal.acm.org/We propose a new global light simulation method for diffuse (or moderately glossy) scenes comprising highly tesselated models with simple topology (e.g., scanned meshes). By using the topological coherence of the surface, we show how to extend a classic Finite Element method called the Master Element: We generalize this method to efficiently handle tessellated models by using mesh parameterization and mesh extrapolation techniques. In addition, we propose a high-order and hierarchical extension of the Master Element method. Our method computes a compact representation of vector irradiance, represented by high-order wavelet bases. For totally diffuse scenes, the so-computed vector irradiance maps can be transformed into light maps. For moderatly glossy scenes, approximated view-dependent lighting can be computed and displayed in real-time by the GPU from the vector irradiance maps. Using our methods, view-dependent solutions for scenes with over one million polygons are computed in minutes and displayed in real time. As with clustering methods, the time complexity of the method is independent on the number of polygons. By efficiently capturing the lighting signal at a suitable scale, the method is made independent of the geometric discretization and solely depends on the lighting complexity. We demonstrate our method in various settings, with both sharp and soft shadows accurately represented by our hierarchical function basis