Shadowing has historically been used to increase the intelligibility of scenes in electron micros-copy and aerial survey. Various methods have been published for the determination of shadows in com-puter synthesized scenes. The display of shadows may make the shape and relative position of objects in such scenes more comprehensible; it is a tech-nique lending vividness and realism to computer an-imation. To date, algorithms for the determination of sha-dows have been restricted to scenes constructed of planar polygons. A simple algorithm is described which utilizes Z-buffer visible surface computation to display shadows cast by objects modelled of smooth surface patches. The method can be applied

The number of polygons comprising interesting architectural models is many more than can be rendered at interactive frame rates. However, due to occlusion by opaque surfaces (e.g., walls), only a small fraction of atypical model is visible from most viewpoints. We describe a method of visibility preprocessing that is efficient andeffective foraxis-aligned oril.ria / architectural m[}dels, A model is subdivided into rectangular cc//.$whose boundaries coincide with major opaque surfaces, Non-opaque p(~rtc~/.rare identified rm cell boundaries. and used to form ana~ju{~’n~y,q)f~/>//con nectingthe cells nfthesubdivisicm. Next. theccl/-r/~-cc/ / visibility is computed for each cell of the subdivisirrn, by linking pairs of cells between which unobstructed.si,q/~t/inr. ~exist. During an interactive ww/krhrm/,q/~phase, an observer with a known ~~sition and\it)M~~~)~t>mov esthrc>ughthe model. At each frame, the cell containingthe observer is identified, and the contents {]fp{>tentially visible cells areretrieved from storage. The set of potentially visible cells is further reduced by culling it against theobserver’s view cone, producing the ~)yt>-r~]-t(>// \ i,$ibi/ify, The contents of the remaining visible cells arc then sent to a graphics pipeline for hidden-surface removal and rendering, Tests onmoderatelyc mnplex 2-D and 3-D axial models reveal substantially reduced rendering loads,

Figure 1: (Left) Uniform 512x512 shadow map and resulting image. (Right) The same with a perspective shadow map of the same size. Shadow maps are probably the most widely used means for the generation of shadows, despite their well known aliasing problems. In this paper we introduce perspective shadow maps, which are generated in normalized device coordinate space, i.e., after perspective transformation. This results in important reduction of shadow map aliasing with almost no overhead. We correctly treat light source transformations and show how to include all objects which cast shadows in the transformed space. Perspective shadow maps can directly replace standard shadow maps for interactive hardware accelerated rendering as well as in high-quality, offline renderers. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation—Bitmap and framebuffer operations; I.3.7 [Computer

Shadows are essential to realistic and visually appealing images, but they are di cult to compute in most display environments. This survey will characterize the various types of shadows, describe most existing shadow algorithms, and for each one discuss their complexities, their advantages and their shortcomings. The types of shadows examined are hard shadows, soft shadows, shadows of transparent objects, and shadows for complex modeling primitives. For each type, we examine shadow algorithms within various rendering techniques. The goal of the survey is to provide readers with enough background and insight on the various methods to allow themtochoose the algorithm best suited to their needs. It is also hoped that our analysis will help identify the areas that need more research, and point to possible solutions.

A new approach to ray tracing is introduced. The definition of a "ray" is extended into a cone by including information on the spread angle and the virtual origin. The advan-tages of this approach, which tries to model light propagation with more fidelity, include a better method of anti-aliasing, a way of calculating fuzzy shadows and dull reflections, a method of calculating the correct level of detail in a procedural model and texture map, and finally, a procedure for faster intersection calculation.

This paper describes an object-space shadow generation algorithm for static polygonal environments illuminated by movable point light sources. The algorithm can be easily implemented on any graphics system that provides fast polygon scan-conversion and achieves near real-time performance for environments of modest size. It combines elements of two kinds of current shadow generation algorithms: two-pass object-space approaches and shadow volume approaches. For each light source a Binary Space Partitioning (BSP) tree is constructed that represents the shadow volume of the polygons facing it. As each polygon's contribution to a light source's shadow volume is determined, the polygon's shadowed and lit fragments are computed by filtering it down the shadow volume BSP tree. The polygonal scene with its computed shadows can be rendered with any polygon-based visible-surface algorithm. Since the shadow volumes and shadows are computed in object space, they can be used for further analysis of the scene. Pseudocode is provided, along with pictures and timings from an interactive implementation.

This thesis presents a volumetric representation for the global illumination within a space based on the radiometric quantity irradiance. We call this representation the irradiance volume. Although irradiance is traditionally computed only for surfaces, its de nition can be naturally extended to all points and directions in space. The irradiance volume supports the reconstruction of believable approximations to the illumination in situations that overwhelm traditional global illumination algorithms. Atheoretical basis for the irradiance volume is discussed and the methods and issues involved with building the volume are described. The irradiance volume method is tested within several situations in which the use of traditional global illumination methods is impractical, and is shown to provide good performance.

We present two efficient image-based approaches for computation and display of high-quality soft shadows from area light sources. Our methods are related to shadow maps and provide the associated benefits. The computation time and memory requirements for adding soft shadows to an image depend on image size and the number of lights, not geometric scene complexity. We also show that because area light sources are localized in space, soft shadow computations are particularly well suited to image-based rendering techniques. Our first approach---layered attenuation maps--- achieves interactive rendering rates, but limits sampling flexibility, while our second method---coherence-based raytracing of depth images---is not interactive, but removes the limitations on sampling and yields high quality images at a fraction of the cost of conventional raytracers. Combining the two algorithms allows for rapid previewing followed by efficient high-quality rendering.

This paper describes a fast, practical algorithm to compute the shadow boundariesin a polyhedral scene illuminated by a polygonal light source. The shadow boundaries divide the faces of the scene into regions such that the structure or "aspect" of the visible area of the light source is constant within each region. The paper also describes a fast, practical algorithm to compute the structure of the visible light source in each region. Both algorithms exploit spatial coherence and are the most efficient yet developed. Given the structure of the visible light source in a region, queries of the form "What specific areas of the light source are visible?" can be answered almost instantly from any point in the region. This speeds up by several orders of magnitude the accurate computation of first level diffuse reflections due to an area light source. Furthermore, the shadow boundaries form a good initial decomposition of the scene for global illumination computations. CR category: I.3.7 [Co...

We define the antiumbra and the antipenumbra of aconvex area light source shining through a sequence of convex areal holes in three dimensions. The antiumbra is the volume from which all points on the light source can be seen. The antipenumbra is the volume from which some, but not all, of the light source can be seen. We show that the antipenumbra is, in general, a disconnected set bounded by portions of quadric surfaces, and describe an implemented O(n 2 ) time algorithm that computes this boundary, where n is the total number of edges comprising the light source and holes. The antipenumbra computation is motivated by a visibility scheme in which we wish to determine the volume visible to an observer looking through a sequenceof transparent convex holes, or portals, connecting adjacent cells in a spatial subdivision. Knowledge of the antipenumbra should also prove useful for rendering shadowed objects. Finally, we have extended the algorithm to compute the planar and quadratic su...