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13
A Fast Shadow Algorithm for Area Light Sources Using Backprojection
, 1994
"... The fast identification of shadow regions due to area light sources is necessary for realistic rendering and for discontinuity meshing for global illumination. A new shadowdetermination algorithm is presented that uses a data structure, called a backprojection, to represent the visible portion of a ..."
Abstract

Cited by 103 (12 self)
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The fast identification of shadow regions due to area light sources is necessary for realistic rendering and for discontinuity meshing for global illumination. A new shadowdetermination algorithm is presented that uses a data structure, called a backprojection, to represent the visible portion of a light source from any point in the scene. A complete discontinuity meshing algorithm is described for polyhedral scenes and area light sources, which includes an important class of light/geometry interactions that have not been implemented before. A fast incremental algorithm for computing backprojections is also described. The use of spatial subdivision, and heuristics based on computed statistics of typical scenes, results in efficient mesh and backprojection computation. Results of the implementation show that the use of the backprojection and discontinuity meshing permits accelerated highquality rendering of shadows using both raycasting and polygonrendering with interpolants. CR C...
Shading Models for Point and Linear Sources
 ACM Transactions on Graphics
, 1985
"... The degree of realism of the shaded image of a threedimensional scene depends on the successful simulation of shading effects. The shading model has two main ingredients, properties of the surface and properties of the illumination falling on it. Most previous work has concentrated on the former ra ..."
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Cited by 25 (3 self)
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The degree of realism of the shaded image of a threedimensional scene depends on the successful simulation of shading effects. The shading model has two main ingredients, properties of the surface and properties of the illumination falling on it. Most previous work has concentrated on the former rather than the latter. This paper presents an improved version for generating scenes illuminated by point and linear light sources. The procedure can include intensity distributions for point light sources and output both umbrae and penumbrae for linear light sources, assuming the environment is composed of convex polyhedra. This paper generalizes Crow’s procedure for computing shadows by using shadow volumes to compute the shading of umbrae and penumbrae. Using shadow volumes caused by the end points of the linear source results in an easy determination of the regions of penumbrae and umbrae on the face prior to shading calculation. This paper also discusses a method for displaying illuminance distribution on a shaded image by using colored isolux contours.
Shadow Volume Reconstruction from Depth Maps
 ACM Transactions on Graphics
, 2000
"... Current graphics hardware can be used to generate shadows using either the shadow volume or shadow map technique. However, the shadow volume technique requires access to a representation of the scene as a polygonal model, and handling the near plane clip correctly and efficiently is difficult; conve ..."
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Cited by 19 (0 self)
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Current graphics hardware can be used to generate shadows using either the shadow volume or shadow map technique. However, the shadow volume technique requires access to a representation of the scene as a polygonal model, and handling the near plane clip correctly and efficiently is difficult; conversely, accurate shadow maps require highprecision texture map data representations, but these are not widely supported. We present a hybrid of the shadow map and shadow volume approaches which does not have these difficulties, and leverages highperformance polygon rendering. The scene is rendered from the point of view of the light source and a sampled depth map is recovered. Edge detection and a templatebased reconstruction technique are used to generate a global shadow volume boundary surface, after which the pixels in shadow can be marked using only a one bit stencil buffer and a singlepass rendering of the shadow volume boundary polygons. The simple form of our templatebased reconstruction scheme simplifies capping the shadow volume after the near plane clip.
Structured Sampling And Reconstruction Of Illumination For Image Synthesis
, 1994
"... An important goal of image synthesis is to achieve accurate, efficient and consistent sampling and reconstruction of illumination varying over surfaces in an environment. A new approach is introduced for the treatment of diffuse polyhedral environments lit by area light sources, based on the identif ..."
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Cited by 16 (3 self)
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An important goal of image synthesis is to achieve accurate, efficient and consistent sampling and reconstruction of illumination varying over surfaces in an environment. A new approach is introduced for the treatment of diffuse polyhedral environments lit by area light sources, based on the identification of important properties of illumination structure. The properties of unimodality and curvature of illumination in unoccluded environments are used to develop a high quality sampling algorithm which includes error bounds. An efficient algorithm is presented to partition the scene polygons into a mesh of cells, in which the visible part of the source has the same topology. A fast incremental algorithm is presented to calculate the backprojection, which is an abstract representation of this topology. The behaviour of illumination in the penumbral regions is carefully studied, and is shown to be monotonic and well behaved within most of the mesh cells. An algorithm to reduce the mesh siz...
Forward Shadow Mapping
 Rendering Techniques ’98, Eurographics
, 1998
"... : Forward shadow mapping is a new approach to realtime shadow generation. The traditional shadow map algorithm maps the pixels in the eye's view backward into the depth buffers of light sources (i.e. shadow maps), which is similiar to and often implemented as an extension to texture mapping. Our ..."
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Cited by 8 (0 self)
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: Forward shadow mapping is a new approach to realtime shadow generation. The traditional shadow map algorithm maps the pixels in the eye's view backward into the depth buffers of light sources (i.e. shadow maps), which is similiar to and often implemented as an extension to texture mapping. Our algorithm reverses this process by using 3D image warping techniques to transform shadow map pixels forward into the eye's view to directly indicate which pixels are lit; it does not interfere with normal texture mapping and easily supports antialiased shadow edges and projective textures. Access to shadow maps and projective textures is in pixelsequential order. This algorithm has advantages when speed of texture mapping becomes the performance bottleneck, which is often the case in visual simulation and game applications. CR Categories and Subject Descriptors: I.3.5 [Computer Graphics]: Picture /Image Generation; I.3.7 [Computer Graphics]: Three Dimensional Graphics and Realism  color...
Shadow Volume Generation from Free Form Surfaces
 In Communicating with Virtual Worlds, Proceedings of CGI’93
, 1993
"... The generation of shadows has occupied the computer graphics community for some time. Several approaches have been successfully developed, but many except ray tracing assume a polygonal approximation of the model. In this paper, an approach is presented that allows one to compute shadow volumes dire ..."
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Cited by 6 (0 self)
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The generation of shadows has occupied the computer graphics community for some time. Several approaches have been successfully developed, but many except ray tracing assume a polygonal approximation of the model. In this paper, an approach is presented that allows one to compute shadow volumes directly from free form models and exploit them for the generation of shadows using a Zbuffer based renderer. A polygonal approximation is not required for either the construction of the shadow volume or for the rendering process. Key Words: Computer graphics, shadows, shadow volumes, parametric surfaces. 1 Introduction Classifications of existing shadow rendering techniques have been presented by several authors [ Bergeron 1986, Crow 1977, Max 1986 ] . The techniques can be categorized into the following six categories. 1. Scanline shadow generation. Comparison is done between all models to determine pairs that can interact to produce shadows [ Appel 1968, Bouknight 1970, Nishita 1991 ] . T...
ThreeDimensional Computer Graphics: A CoordinateFree Approach
, 1992
"... Data Type ............ 14 2.4 The Simple Graphics Package .............. 19 2.4.1 TwoDimensional Windowing and Viewporting 19 2.5 TwoDimensional Line Clipping ............. 23 2.5.1 CohenSutherland Line Clipping ........ 25 2.5.2 The Clipping Divider .............. 27 2.6 Windowing and Viewportin ..."
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Cited by 6 (0 self)
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Data Type ............ 14 2.4 The Simple Graphics Package .............. 19 2.4.1 TwoDimensional Windowing and Viewporting 19 2.5 TwoDimensional Line Clipping ............. 23 2.5.1 CohenSutherland Line Clipping ........ 25 2.5.2 The Clipping Divider .............. 27 2.6 Windowing and Viewporting Revisited ......... 28 CHAPTER 3. Coordinatefree Geometric Programming I 31 3.1 Problems with the Coordinatebased Approach .... 31 3.2 Aftinc Spaces ....................... 33 3.3 Euclidean Geometry ................... 42 3.3.1 The Inner Product ................ 43 3.4 Frames ........................... 44 3.5 *Matrix Representations of Points and Vectors .... 49 3.6 Aftinc Transformations .................. 51 3.7 *Matrix Representations of Aftinc Transformations . . 58 3.8 Ambiguity Revisited ................... 60 3.9 CoordinateFree Line Clipping ............. 62 3.10 A Brief Review of Linear Algebra ............ 67 CHAPTER 4. ThreeDimensional Wireframe Viewing 69 4.1
Realism in Computer Graphics: A Survey
, 1987
"... This paper will survey most of the major issues that one must deal with when generating realistic images+. Webegin with an overviewofthe rendering process and a quick reviewofvisible surface determination algorithms. We t hen discuss, in more detail, shading, antialiasing, texture mapping, shadows, ..."
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Cited by 3 (0 self)
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This paper will survey most of the major issues that one must deal with when generating realistic images+. Webegin with an overviewofthe rendering process and a quick reviewofvisible surface determination algorithms. We t hen discuss, in more detail, shading, antialiasing, texture mapping, shadows, optical effects and close with a discussion of modeling primitives
A shadow algorithm for CSG
 Computers and Graphics
, 1991
"... An algorithm is presented for constructing shadow volumes for CSG objects. For each primitive solid, the algorithm calculates a tree of shadow volumes to model the shadows generated by the shadowgenerating parts of the boundary of the primitive. The shadow of the complete CSG object is the union of ..."
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Cited by 1 (0 self)
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An algorithm is presented for constructing shadow volumes for CSG objects. For each primitive solid, the algorithm calculates a tree of shadow volumes to model the shadows generated by the shadowgenerating parts of the boundary of the primitive. The shadow of the complete CSG object is the union of these shadow trees. An implementation of the algorithm is described for a scanline display algorithm for CSG objects with polygonal primitives. 1.