Andrew Woo

A survey of shadow algorithms

The various types of shadows are characterized. Most existing shadow algorithms are described, and their complexities, advantages, and shortcomings are discussed. Hard shadows, soft shadows, shadows of transparent objects, and shadows for complex modeling primitives are considered. For each type, shadow algorithms within various rendering techniques are examined. The aim is to provide readers with enough background and insight on the various methods to allow them to choose the algorithm best suited to their needs and to help identify the areas that need more research and point to possible solutions.<<ETX>>

The shadow depth map revisited

Publisher Summary The shadow-depth map has proven to be an effective shadow determination approach in image synthesis. It can handle any class of geometric primitives with equal ease. It is the only shadow approach that requires a storage complexity independent of the number of objects in the scene, which is an advantage when it comes to complex scenes. However, the depth map is prone to aliasing problems, of which some have been improved using some filtering techniques. This chapter discusses the moire-pattern aliasing problem and presents a superior solution. The basic shadow-depth-map approach is very simple. A SampleShadow routine is called to compare the depth value for each applicable depth-map cell with that for the current intersection point. If there is more than one surface that hits the depth-map cell, then the depth-map cell value is assigned to be an average between the first two visible surfaces with respect to the light source. Special care is required at the outer limits of a spotlights cone of illumination. The changes made to the shadow-depth-map approach work quite well, even at a low resolution of 256 × 256. A 1,024 × 1,024 resolution depth map is not always necessary for realistic shadows.

It's really not a rendering bug, you see

Most rendering algorithms deliberately employ approximations and other shortcuts for efficiency. These economies-not coding errors-produce characteristic image artifacts. This article classifies the best-known varieties. We wrote this article in the hope of saving programmers a lot of time debugging something that is really not a bug, but instead a limitation of the algorithm. Our taxonomy is not exhaustive, but it does include many common rendering problems that we have encountered over the years. Most of these limitations can be circumvented with the proposed solutions. In reality, there are more workarounds than true solutions. This imbalance warrants more research into proper solutions to these and similar problems.

Design and implementation of the Maya Renderer

Maya is the new 3D software package recently released by Alias I Wavefront for creating state of the art character animation and visual effects. Built on a next generation advanced architecture, Maya delivers high speed interaction and high productivity for its users. In the Fall of 1995, the Rendering Team at Alias/Wavefront started from scratch to design and implement a renderer for the Maya project. This was a very challenging task, requiring the efficient generation of high quality images for a next generation 3D application that was still under development. In addition, we were expected to match or exceed the capabilities of our existing popular rendering products (as well as those from our competitors). In January of 1998, the all new renderer was delivered with Maya 1.0. It includes a comprehensive user interface that is well integrated with the rest of the system, and a batch renderer that is capable of efficiently generating a full spectrum of high quality visual effects. Currently, there are high end computer graphics (CG) productions in progress that are using the Maya Renderer. We concentrate on our batch renderer implementation effort. We describe the philosophy, design decisions, and the tasks we set out to achieve in 1995. We then evaluate the delivered system based on images generated with the renderer.

Feature-based Displacement Mapping

Displacement mapping was originally created as a rendering tool to provide small-scale modulation of an underlying smooth surface. However, it has now emerged as a sculpting tool, to the extent that complex geometry can effectively be added to a scene at rendering time. The attendant complexity of displacement maps is placing increased demands on rendering systems, from quality, performance, and memory perspectives. While adequate solutions exist within scanline rendering architectures, good general solutions have been difficult to come by in ray-traced or hardware-based environments, or in situations in which a complete displaced surface is desired. We present an approach to the rendering of displacement mapped surfaces that scales with the complexity of the displacement map, with an eye to minimizing the amount of additional geometry generated by the mapping process. We perform a feature analysis of displacement maps, aggregate these features, and map them onto geometry in space. This approach affords a significant degree of complexity control, it permits feature-based tessellation of surfaces, and it is amenable to use in ray-traced, scanline, or hardware accelerated settings. This kind of feature analysis naturally applies to other classes of texture mapping as well.

Efficient shadow computations in ray tracing

Two techniques to speed up shadow computations in ray tracing are examined. The first, atomic adaptive sampling, is intended for any light type, such as directional, spot, point, linear, and area lights, in antialiasing, while the second, plane-vertex checking, specifically accelerates shadow computation of linear and area lights. The basic ideas can be extended to other ray types and, for the plane-vertex check, to radiosity applications as well. Existing surveys explain the fundamentals and provide references to intersection culler and shadow algorithms.<<ETX>>

Chordlength texturing of spline surfaces

This paper presents an inexpensive way to provide (s, t)texture co-ordinates of a spline surface, which mitigates texture compression and stretching artifacts. The approach employs a chordlength approximation based on the original spline-surface parameterization. Its success can be seen in existing Alias|Wavefront renderers since 1991.

3D data visualization: The advantages of volume graphics and big data to support geologic interpretation

The ability to integrate diverse data types from multiple live and simulated sources, manipulate them dynamically, and deploy them in integrated, visual formats and in mobile settings provides significant advantages. We have reviewed some of the benefits of volume graphics and the use of big data in the context of 3D visualization case studies, in which inherent features, such as representation efficiencies, dynamic modifications, cross sectioning, and others, could improve interpretation processes and workflows.

Focus on ACM SIGGRAPH Canadian chapters

There are currently four active ACM SIGGRAPH chapters in Canada. We decided to get together to write up a review of our respective ACM SIGGRAPH chapter activities, because these activities may be of interest to the Canadian and overall ACM SIGGRAPH community. The Canadian chapters include:<i>Atlantic</i><br></br>Heather Fowler: Chair<br></br><b>http://atlantic-canadian.siggraph.org</b><i>Montreal</i><br></br>Myriam Côté, Chair<br></br><b>http://montreal.siggraph.org</b><i>Toronto</i><br></br>Adele Newton, Chair<br></br><b>http://toronto.siggraph.org</b><i>Vancouver</i><br></br>Andrew Woo, Chair<br></br><b>http://vancouver.siggraph.org</b>If you are interested in being a volunteer or a speaker (especially if you are from out of town), please contact the appropriate chapters (see addresses above), and we will be more than happy to talk to you. We hope you enjoy the review of the ACM SIGGRAPH Canadian chapters!