bluuebunny/crossref_metadata_2025 huggingface dataset:
Coping with friction for non-penetrating rigid body simulation
Authors: Baraff David
Published: November 2005

Algorithms and computational complexity measures for simulating the motion of contacting bodies with friction are presented. The bodies are restricted to be perfectly rigid bodies that contact at finitely many points. Contact forces between bodies must satisfy the Coulomb model of friction. A traditional principle of mechanics is that contact forces are impulsive if and only if non-impulsive contact forces are insufficient to maintain the non-penetration constraints between bodies. When friction is allowed, it is known that impulsive contact forces can be necessary even in the absence of collisions between bodies. This paper shows that computing contact forces according to this traditional principle is likely to require exponential time. An analysis of this result reveals that the principle for when impulses can occur is too restrictive, and a natural reformulation of the principle is proposed. Using the reformulated principle, an algorithm with expected polynomial time behaviour for computing contact forces is presented.
Design and simulation of opera lighting and projection effects
Authors: Dorsey Julie O'B. , Sillion Françis X. , Greenberg Donald P.
Published: November 2005

A major problem challenging opera designers is the inability to co-ordinate lighting, projection systems, and set designs in the preliminary planning phase. New computer graphics techniques, which provide the set and lighting designer the opportunity to evaluate, test, and control opera designs prior to the construction of full scale systems are presented. These techniques---light source input, simulation of directional lighting, modeling of scenic projection systems, and full three-dimensional simulation---show the potential for the use of computer graphics in theater design.The light source input component consists of a program for assigning light source attributes with a set of theater lighting icons. This module allows a designer to specify light source characteristics in a way familiar to the discipline and to make preliminary evaluations of the lighting conditions.An extended progressive radiosity method is introduced to simulate the directional lighting characteristics which are specified by the input program.A new projection approach is presented to simulate the optical effects of scenic projectors. In addition, a solution to the distortion problem produced by angular projections is described.The above components are integrated to produce full three-dimensional simulations of the global illumination effects in an opera scene.
Visibility preprocessing for interactive walkthroughs
Authors: Teller Seth J. , Séquin Carlo H.
Published: November 2005

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 a typical model is visible from most viewpoints.We describe a method of visibility preprocessing that is efficient and effective for axis-aligned or
axial
architectural models. A model is subdivided into rectangular
cells
whose boundaries coincide with major opaque surfaces. Non-opaque
portals
are identified on cell boundaries, and used to form an
adjacency graph
connecting the cells of the subdivision. Next, the
cell-to-cell
visibility is computed for each cell of the subdivision, by linking pairs of cells between which unobstructed
sightlines
exist.During an interactive
walkthrough
phase, an observer with a known position and
view cone
moves through the model. At each frame, the cell containing the observer is identified, and the contents of potentially visible cells are retrieved from storage. The set of potentially visible cells is further reduced by culling it against the observer's view cone, producing the
eye-to-cell visibility
. The contents of the remaining visible cells are then sent to a graphics pipeline for hidden-surface removal and rendering.Tests on moderately complex 2-D and 3-D axial models reveal substantially reduced rendering loads.
Model-based matching and hinting of fonts
Authors: Hersch Roger D. , Betrisey Claude
Published: November 2005

In today's digital computers, phototypesetters and printers, typographic fonts are mainly given by their outline descriptions. Outline descriptions alone do not provide any information about character parts like stems serifs, shoulders, and bowls. But, in order to produce the best looking characters at a given size on a specific printer, non-linear operations must be applied to parts of the character shape. At low-resolution, grid-fitting of character outlines is required for generating nice and regular raster characters. For this reason, grid-fitting rules called hints are added to the character description. Grid-fitting rules require as parameters certain characteristic points within the shape outlines. In order to be able to detect these characteristic points in any given input font, a topological model representing the essence of the shapes found in typographic latin typefaces is proposed. This model includes sufficient information for matching existing non-fancy outline fonts to the model description. For automatic hint generation, a table of applicable hints is added into the topological model description. After matching a given input shape to the model, hints which can be applied to the shape of the given font are taken and added to its outline description. Furthermore, a structural description of individual letter shape parts using characteristic model points can be added to the model. Such a description provides knowledge about typographic structure elements like stems, serifs and bowls.
Digital halftoning with space filling curves
Authors: Velho Luiz , Gomes Jonas de Miranda
Published: November 2005

This paper introduces a new digital halftoning technique that uses space filling curves to generate aperiodic patterns of clustered dots. This method allows the parameterization of the size of pixel clusters, which can vary in one pixel steps. The algorithm unifies, in this way, the dispersed and clustered-dot dithering techniques.
Efficient antialiased rendering of 3-D linear fractals
Authors: Hart John C. , DeFanti Thomas A.
Published: November 2005

Object instancing is the efficient method of representing an hierarchical object with a directed graph instead of a tree. If this graph contains a cycle then the object it represents is a linear fractal. Linear fractals are difficult to render for three specific reasons: (1) ray-fractal intersection is not trivial, (2) surface normals are undefined and (3) the object aliases at all sampling resolutions.Ray-fractal intersections are efficiently approximated to sub-pixel accuracy using procedural bounding volumes and a careful determination of the size of a pixel, giving the perception that the surface is infinitely detailed. Furthermore, a surface normal for these non-differentiable surfaces is defined and analyzed. Finally, the concept of antialiasing "covers" is adapted and used to solve the problem of sampling fractal surfaces.An initial bounding volume estimation method is also described, allowing a linear fractal to be rendered given only its iterated, function system. A parallel implementation of these methods is described and applications of these results to the rendering of other fractal models are given.
An object-oriented framework for the integration of interactive animation techniques
Authors: Zeleznik Robert C. , Conner D. Brookshire , Wloka Matthias M. , Aliaga Daniel G. , Huang Nathan T. , Hubbard Philip M. , Knep Brian , Kaufman Henry , Hughes John F. , van Dam Andries
Published: November 2005

We present an interactive modeling and animation system that facilitates the integration of a variety of simulation and animation paradigms. This system permits the modeling of diverse objects that change in shape, appearance, and behaviour over time. Our system thus extends modeling tools to include animation controls. Changes can be effected by various methods of control, including scripted, gestural, and behavioral specification. The system is an extensible testbed that supports research in the interaction of disparate control methods embodied in controller objects. This paper discusses some of the issues involved in modeling such interactions and the mechanisms implemented to provide solutions to some of these issues.The system's object-oriented architecture uses delegation hierarchies to let objects change all of their attributes dynamically. Objects include displayable objects, controllers, cameras, lights, renderers, and user interfaces. Techniques used to obtain interactive performance include the use of data-dependency networks, lazy evaluation, and extensive caching to exploit inter- and intra-frame coherency.
Inkwell
Authors: Litwinowicz Peter C.
Published: November 2005

Inkwell, an experimental 2 1/2-D keyframe animation system, is the subject of this paper. Inkwell provides an intuitive user interface for creating and animating polygons, ellipses and splines. These primitives may be outlined and filled with a variety of patterns to create animated diagrams, graphs and charts, and simple characters and cartoons. Inkwell also has a patch primitive that facilitates deformation and animation of textured regions. The system provides editing features that include shape and timing control as well as digital filtering of parameters. Finally, Inkwell has deformation primitives that enable an animator to warp geometry in an intuitive manner. Inkwell was used to produce
Pigment Promenade
, a computer animated short shown at SIGGRAPH 1990.
An efficient antialiasing technique
Authors: Wu Xiaolin
Published: November 2005

An intuitive concept of antialiasing is developed into very efficient antialiased line and circle generators that require even less amount of integer arithmetic than Bresenham's line and circle algorithms. Unlike its predecessors, the new antialiasing technique is derived in spatial domain (raster plane) under a subjectively meaningful error measure to preserve the dynamics of curve and object boundaries. A formal analysis of the new antialiasing technique in frequency domain is also conducted. It is shown that our antialiasing technique computes the same antialiased images as Fujimoto-Iwata's algorithm but at a fraction of the latter's computational cost. The simplicities of the new antialiased line and circle generators also mean their easy hardware implementations.
A progressive multi-pass method for global illumination
Authors: Chen Shenchang Eric , Rushmeier Holly E. , Miller Gavin , Turner Douglass
Published: November 2005

A new progressive global illumination method is presented which produces approximate images quickly, and then continues to systematically produce more accurate images. The method combines the existing methods of progressive refinement radiosity, Monte Carlo path tracing and light ray tracing. The method does not place any limitation on surface properties such as ideal Lambertian or mirror-like. To increase efficiency and accuracy, the new concepts of light source reclassification, caustics reconstruction, Monte Carlo path tracing with a radiosity preprocess and an interruptible radiosity solution are introduced. The method presents the user with most useful information about the scene as early as possible by reorganizing the method into a radiosity pass, a high frequency refinement pass and a low frequency refinement pass. The implementation of the method is demonstrated, and sample images are presented.
NC machining with G-buffer method
Authors: Saito Takafumi , Takahashi Tokiichiro
Published: November 2005

The G-buffer method is applied to NC machining. A total NC system is created that consists of all essential functions, such as tool path generation, path verification, and feed rate control. Moreover, any combination of object surface and tool shape is acceptable. By utilizing G-buffers created from a parallel projection, the required NC functions are realized as image processing operations. This ensures that the NC software is independent from surface description. Conventional rendering software can be used to make the G-buffers. Any surface can be milled if it can be rendered by parallel projection. Tool shape changes can be easily handled by changing the image processing filters. 3D examples of geometric surfaces, mesh data, and volume data are milled with this method, and the results show that the method is very effective.
Piecewise surface flattening for non-distorted texture mapping
Authors: Bennis Chakib , Vézien Jean-Marc , Iglésias Gérard
Published: November 2005

This paper introduces new techniques for interactive piecewise flattening of parametric 3-D surfaces, leading to a non-distorted, hence realistic, texture mapping. Cuts are allowed on the mapped texture and we make a compromise between discontinuities and distortions. These techniques are based on results from differential geometry, more precisely on the notion of "
geodesic curvature
": isoparametric curves of the surface are mapped, in a constructive way, onto curves in the texture plane with preservation of geodesic curvature at each point. As an application, we give a concrete example which is a first step towards an efficient and robust CAD tool for shoe modeling.
Generalized implicit functions for computer graphics
Authors: Sclaroff Stan , Pentland Alex
Published: November 2005

We describe a method of generalizing implicit functions by use of modal deformations and displacement maps. Modal deformations, also known as free vibration modes, are used to describe the overall shape of a solid, while displacement maps provide local and fine surface detail by offsetting the surface of the solid along its surface normals. The advantage of this approach to geometric description is that collision detection and dynamic simulation become simple and inexpensive even for complex shapes. In addition, we outline an efficient method for fitting such models to three dimensional point data.
Deformable curve and surface finite-elements for free-form shape design
Authors: Celniker George , Gossard Dave
Published: November 2005

The finite element method is applied to generate primitives that build continuous deformable shapes designed to support a new free-form modeling paradigm. The primitives autonomously deform to minimize an energy functional subject to user controlled geometric constraints and loads. The approach requires less user input than conventional free-form modeling approaches because the shape can be parameterized independently of the number of degrees of freedom needed to describe the shape.Both a curve and a surface finite element are developed. The properties of these geometric primitives have been engineered to support an interactive three phase approach for defining very fair free-form shapes as found in automobiles, ship hulls and car bodies. The shape's character lines or folds and edges are defined with deformable curve segments. These character lines are then "skinned" with a deformable surface. The final shape is sculpted interactively by applying loads to the surface to control the surface shape between character lines. Shapes created with this technique enjoy the advantage that they are already meshed for further finite element analysis.
Sculpting
Authors: Galyean Tinsley A. , Hughes John F.
Published: November 2005

We present a new interactive modeling technique based on the notion of sculpting a solid material. A sculpting tool is controlled by a 3D input device and the material is represented by voxel data; the tool acts by modifying the values in the voxel array, much as a "paint" program's "paintbrush" modifies bitmap values. The voxel data is converted to a polygonal surface using a "marching-cubes" algorithm; since the modifications to the voxel data are local, we accelerate this computation by an incremental algorithm and accelerate the display by using a special data structure for determining which polygons must be redrawn in a particular screen region. We provide a variety of tools: one that cuts away material, one that adds material, a "sandpaper" tool, a "heat gun," etc. The technique provides an intuitive direct interaction, as if the user were working with clay or wax. The models created are free-form and may have complex topology; however, they are not precise, so the technique is appropriate for modeling a boulder or a tooth but not for modeling a crankshaft.
Hierarchical splatting
Authors: Laur David , Hanrahan Pat
Published: November 2005

This paper presents a progressive refinement algorithm for volume rendering which uses a pyramidal volume representation. Besides storing average values, the pyramid stores estimated error, so an octtree can be fit to the pyramid given a user-supplied precision. This octtree is then drawn using a set of splats, or footprints, each scaled to match the size of the projection of a cell. The splats themselves are approximated with RGBA Gouraud-shaded polygons, so that they can be drawn efficiently on modern graphics workstations. The result is a real-time rendering algorithm suitable for interactive applications.
Generating textures on arbitrary surfaces using reaction-diffusion
Authors: Turk Greg
Published: November 2005

This paper describes a biologically motivated method of texture synthesis called
reaction-diffusion
and demonstrates how these textures can be generated in a manner that directly matches the geometry of a given surface. Reaction-diffusion is a process in which two or more chemicals diffuse at unequal rates over a surface and react with one another to form stable patterns such as spots and stripes. Biologists and mathematicians have explored the patterns made by several reaction-diffusion systems. We extend the range of textures that have previously been generated by using a cascade of multiple reaction-diffusion systems in which one system lays down an initial pattern and then one or more later systems refine the pattern. Examples of patterns generated by such a cascade process include the clusters of spots on leopards known as rosettes and the web-like patterns found on giraffes. In addition, this paper introduces a method which reaction-diffusion textures are created to match the geometry of an arbitrary polyhedral surface. This is accomplished by creating a mesh over a given surface and then simulating the reaction-diffusion process directly on this mesh. This avoids the often difficult task of assigning texture coordinates to a complex surface. A mesh is generated by evenly distributing points over the model using relaxation and then determining which points are adjacent by constructing their Voronoi regions. Textures are rendered directly from the mesh by using a weighted sum of mesh values to compute surface color at a given position. Such textures can also be used as bump maps.
Reaction-diffusion textures
Authors: Witkin Andrew , Kass Michael
Published: November 2005

We present a method for texture synthesis based on the simulation of a process of local nonlinear interaction, called reaction-diffusion, which has been proposed as a model of biological pattern formation. We extend traditional reaction-diffusion systems by allowing anisotropic and spatially non-uniform diffusion, as well as multiple competing directions of diffusion. We adapt reaction-diffusion system to the needs of computer graphics by presenting a method to synthesize patterns which compensate for the effects of non-uniform surface parameterization. Finally, we develop efficient algorithms for simulating reaction-diffusion systems and display a collection of resulting textures using standard texture- and displacement-mapping techniques.
Spot noise texture synthesis for data visualization
Authors: van Wijk Jarke J.
Published: November 2005

The use of stochastic texture for the visualization of scalar and vector fields over surfaces is discussed. Current techniques for texture synthesis are not suitable, because they do not provide local control, and are not suited for the design of textures. A new technique,
spot noise
, is presented that does provide these features. Spot noise is synthesized by addition of randomly weighted and positioned spots. Local control of the texture is realized by variation of the spot. The spot is a useful primitive for texture design, because, in general, the relations between features of the spot and features of the texture are straightforward. Various examples and applications are shown. Spot noise lends itself well for the synthesis of texture over curved surfaces, and is therefore an alternative to solid texturing. The relations of spot noise with a variety of other techniques, such as radom faults, filtering, sparse convolution, and particle systems, are discussed. It appears that spot noise provides a new perspective on those techniques.
Artificial evolution for computer graphics
Authors: Sims Karl
Published: November 2005

This paper describes how evolutionary techniques of variation and selection can be used to create complex simulated structures, textures, and motions for use in computer graphics and animation. Interactive selection, based on visual perception of procedurally generated results, allows the user to direct simulated evolutions in preferred directions. Several examples using these methods have been implemented and are described. 3D plant structures are grown using fixed sets of genetic parameters. Images, solid textures, and animations are created using mutating symbolic lisp expressions. Genotypes consisting of symbolic expressions are presented as an attempt to surpass the limitations of fixed-length genotypes with predefined expression rules. It is proposed that artificial evolution has potential as a powerful tool for achieving flexible complexity with a minimum of user input and knowledge of details.
Computer animation of knowledge-based human grasping
Authors: Rijpkema Hans , Girard Michael
Published: November 2005

The synthesis of human hand motion and grasping of arbitrary shaped objects is a very complex problem. Therefore high-level control is needed to perform these actions. In order to satisfy the kinematic and physical constraints associated with the human hand and to reduce the enormous search space associated with the problem of grasping objects, a knowledge based approach is used. A three-phased scheme is presented which incorporates the role of the hand, the object, the environment and the animator. The implementation of a hand simulation system HANDS is discussed.
Pictures, poseurs, and posers
Authors: Rueff Sylvie J.
Published: November 2005

"The only thing you can do with computer graphics is make pretty pictures." That was the thinking of most people a decade ago, and it still is the opinion of all too many people. At the same time, an enormous amount of attention is now being paid to the use of computer based pictures in the realm of the sciences.Because of concerns about weaknesses in mathematics and science, there is a movement to make math and science more entertaining. Certainly it is of value to make math and science more interesting and more accessible, and pictures can be great communicators, as shown by the work done in
The Mechanical Universe
and
Mathematics
! Science and math are about understanding, and understanding requires that people participate, ask questions, observe well, discover clues, and find solutions. Both of the animations mentioned above are used within the context of the classroom, with support materials.Many people are producing pictures from data in the laboratory. This process of creating images is exhilarating, but not all images created with the use of a computer are scientifically useful. It is a challenge to make good pictures which focus either on the investigation or on the attributes of the data being examined. These should be accurate and contain all the information required for understanding the data.
Visualization '91 workshop report
Authors: Butler David M. , Hansen Charles
Published: November 2005

The Workshop on Scientific Visualization Environments at Visualization '91 was organized with several purposes in mind. First and foremost was to bring together widely dispersed researchers so they could share information in a relatively informal and interactive environment. The organizers believed this would establish working relationships between the participants, which was a second purpose. It was hoped that a workshop could generate a focus and identify important research directions in the field. Finally, we believed the workshop report could provide a useful overview to a broader audience.With these purposes in mind, we established two specific objectives: (i) review the state of the art and (ii) identify key research issues and directions. Reaching these objectives in a short two day workshop would require an effective mechanism for organizing the discussions. The organizing principle we chose was a software design principle suggested by Dijkstra [ 1 ] some twenty years ago: the notion of an abstract machine. We considered a visualization environment as a special purpose, very high level computer ideally suited to the needs of scientific visualization. We then organized the workshop discussions around the questions of what the memory (data types), instruction set (operations) and control mechanisms (programming interfaces) of this machine might be.Using this organizing principle, we established the following agenda: Monday morning: position statements. Each participant presented a ten minute summary of their position paper Monday afternoon: data types and interfaces What are the (abstract) data types on which a visualization environment is based? What are the interfaces for importing and exporting data from the environment? Tuesday morning: control structures and architecture What are the mechanisms for sequencing and combining the primitive operations provided by the data types. What are the interaction and programming interfaces to the environment? Tuesday afternoon early: reference model Do we understand visualization environments well enough to construct a useful general model of their structure and function? Tuesday afternoon late: other issues and summary What issues are not addressed in the other sections? What have we accomplished? For each section we followed a simple procedure. The organizers presented introductory remarks consisting of a brief review of the state of the art and identification of research issues. The introductory remarks served as a starting point for discussions which followed. Participants were given copies of the organizers' remarks and asked to take notes for contribution to the report. The notes were collected at the end of the workshop and collated into this report. In addition, participants reviewed the first draft of the report and made additional contributions.
Directory of educational discounts, donations, and grants
Authors: Callihan Hubert
Published: November 2005

The information included here was compiled using responses from 36 hardware and software vendors who were among 189 exhibitors attending the 1991 SIGGRAPH Conference in Las Vegas. Product descriptions and other details vary, but in most cases, provide enough information for educators to inquire further about opportunities to obtain products at a discount, as a donation, or possibly as a grant in connection with academic research. Companies responding that have neither educational discount, donation nor grant programs are not listed. SIGGRAPH encourages its conference exhibitors to submit a Directory listing for the benefit of educators. Listing a company or product in the Directory does not imply endorsement by either ACM or SIGGRAPH. Neither does it imply that the listing reflects the most recent policy of any vendor in effect after November 15, 1991. Educators should confirm any discount opportunities directly with the vendor.
Visualization Research at Worcester Polytechnic Institute
Authors: Ward Matthew
Published: November 2005

Visualization research at W.P.I. evolved from a series of interdisciplinary discussions during the summer of 1989. Faculty from the departments of Biology and Biotechnology, and from Chemical, Civil, Electrical, and Mechanical Engineering each identified problem areas
such as genetic
sequence analysis, chemical separation, crystal growth monitoring, global positioning, and analysis of pavement materials. Prototype visualization techniques to address. these areas were developed and evaluated, and the most promising techniques were the focus of research efforts of several faculty and graduate students over the next few years. Most techniques have been generalized to a variety of application areas. A few of these efforts and the lessons learned from them are outlined below.
Feature-based image metamorphosis
Authors: Beier Thaddeus , Neely Shawn
Published: November 2005

A new technique is presented for the metamorphosis of one digital image into another. The approach gives the animator high-level control of the visual effect by providing natural feature-based specification and interaction. When used effectively, this technique can give the illusion that the photographed or computer generated subjects are transforming in a fluid, surrealistic, and often dramatic way. Comparisons with existing methods are drawn, and the advantages and disadvantages of each are examined. The new method is then extended to accommodate keyframed transformations between image sequences for motion image work. Several examples are illustrated with resulting images.
Photographic rendering of environmental graphics in context
Authors: Morlan Jenny
Published: November 2005

Environmental graphics is an interdisciplinary course in which art and computer science students produce professional quality presentations of original signage in an image that visualizes its appearance in an outdoor setting. This area of graphic design has been identified as one of the few where the application of computer graphics has not been fully developed. Previously, this task has been accomplished through expensive, tedious photographic retouching, or by less realistic felt-tipped marker renderings.The structure of this course is easily adaptable to other areas of applied and design art, including package design, industrial design and installation art, and requires only modest computing resources. The course is taught by an artist and a computer scientist, and satisfies degree requirements for the major in both departments.
SIGKids'92
Authors: Conn Coco
Published: November 2005

SIGGRAPH '92 in Chicago offered the future to a group of young students by inviting them to participate in the SIGKids '92 learning lab workshop. Computers, video, multimedia, LEGO/Logo, digital journal keeping, access to the Internet and interactive projects were explored by these bright young minds.At most education conferences, there is alot of talk about what does, could or should take place in the classroom. SIGKids went a step further. It created an ideal situation; a learning lab run by the students and their mentors. Volunteer mentors generously donated their time and skills and came from the university, industry and research communities.
Real-time shaded NC milling display
Authors: Van Hook Tim
Published: November 2005

The real-time shaded display of a solid model being milled by a cutting tool following an NC path is attained by the image-space Boolean subtraction of solid objects. The technique is suitable for implementation in microcode in a raster graphic display processor. Update rates of 10 cutting operations per second are typical.
Image rendering by adaptive refinement
Authors: Bergman Larry , Fuchs Henry , Grant Eric , Spach Susan
Published: November 2005

This paper describes techniques for improving the performance of image rendering on personal workstations by using CPU cycles going idle while the user is examining a static image on the screen. In that spirit, we believe that
a renderer's work is never done
. Our goal is to convey the most information to the user as early as possible, with image quality constantly improving with time. We do this by first generating a crude image rapidly and then adaptively refining it where necessary as long as the user does not change viewing parameters. The renderer operates in a succession of phases, first displaying only vertices of polygons, next polygon edges, then flat shading polygons, then shadowing polygons, then Gouraud shading polygons, then Phong shading polygons, and finally anti-aliasing. Performance is enhanced by each phase using results from previous phases and trimming the amount of data needed by the next phase. In this way, only a fraction of the pixels in an image may be Phong shaded while the rest may be Gouraud or flat shaded. Similarly anti-aliasing is performed only on pixels around which there is significant color change. The system features fast response to user intervention, encourages user intervention at any moment, and makes useful the idle cycles in a personal computer.
The definition and rendering of terrain maps
Authors: Miller Gavin S P
Published: November 2005

This paper examines three methods, two existing and one new, for the generation of fractals based on recursive subdivision. Both existing methods are found to have defects, which are not present in the new method. A parallel processing algorithm is proposed for the rendering of height fields which is exact and distributes the load evenly between the processors. A method is described for the 'fan-tracing' of height fields to allow the realistic simulation of water reflections.
The synthesis of cloth objects
Authors: Weil Jerry
Published: November 2005

In image synthesis, cloth objects such as clothes are most often modelled as textures mapped onto rigid surfaces. However, in order to represent such objects more realistically, their physical properties must be examined. This paper describes a method for modelling cloth material hanging in three dimensions when supported by any number of constraint points. The cloth synthesized with this model contains folds and appears more realistic than simple texture mapping. This paper also describes a method for rendering the cloth once its free-hanging shape has been determined.The computation of the surface of a free-hanging cloth is performed in two stages. The first stage approximates the shape of the surface which is interior to the constraint points, and the second stage performs a relaxation process on all points on the surface to arrive at a close approximation to its shape. The rendering of the surfaces is done using a ray-tracer which treats the surface as a mesh of line segments.
Modeling waves and surf
Authors: Peachey Darwyn R.
Published: November 2005

Although modeling natural phenomena is recognized as one of the greatest challenges of computer graphics, relatively little time has been spent on modeling ocean waves. The model presented in this paper is suitable for the rendering and animation of waves approaching and breaking on a sloping beach. Waveforms consist of a phase function which correctly produces wave refraction and other depth effects, and a wave profile which changes according to wave steepness and water depth. Particle systems are used to model the spray produced by wave breaking and collisions with obstacles. A scanline algorithm for displaying the wave surface is presented, along with a method of integrating separately rendered particle systems with other surfaces. Hidden surface removal for both waves and particles is done using a novel variation of the A-buffer technique. Methods of implementing the model are presented and compared with previous rendering techniques.
Fast Phong shading
Authors: Bishop Gary , Weimer David M.
Published: November 2005

Computer image generation systems often represent curved surfaces as a mesh of planar polygons that are shaded to restore a smooth appearance. Phong shading is a well known algorithm for producing a realistic shading but it has not been used by real-time systems because of the 3 additions, 1 division, and 1 square-root required per pixel for its evaluation. We describe a new formulation for Phong shading that reduces the amount of computation per pixel to only 2 additions for simple Lambertian reflection and 5 additions and 1 memory reference for Phong's complete reflection model. We also show how to extend our method to compute the specular component with the eye at a finite distance from the scene rather than at infinity as is usually assumed. The method can be implemented in hardware for real-time applications or in software to speed image generation for almost any system.
Atmospheric illumination and shadows
Authors: Max Nelson L.
Published: November 2005

The shadow volume algorithm of Frank Crow was reorganized to provide information on the regions of illuminated space in front of each visible surface. This information is used to calculate the extra intensity due to atmospheric scattering, so when the atmosphere is partly in shadow, columns of scattered light will be visible. For efficiency in sorting the shadow edges, the image is computed in polar coordinates.
Constructive solid geometry for polyhedral objects
Authors: Laidlaw David H. , Trumbore W. Benjamin , Hughes John F.
Published: November 2005

Constructive Solid Geometry (CSG) is a powerful way of describing solid objects for computer graphics and modeling. The surfaces of any primitive object (such as a cube, sphere or cylinder) can be approximated by polygons. Being abile to find the union, intersection or difference of these objects allows more interesting and complicated polygonal objects to be created. The algorithm presented here performs these set operations on objects constructed from convex polygons. These objects must bound a finite volume, but need not be convex. An object that results from one of these operations also contains only convex polygons, and bounds a finite volume; thus, it can be used in later combinations, allowing the generation of quite complicated objects. Our algorithm is robust and is presented in enough detail to be implemented.
Hairy brushes
Authors: Strassmann Steve
Published: November 2005

Paint brushes are modeled as a collection of bristles which evolve over the course of the stroke, leaving a realistic image of a
sumi
brush stroke. The major representational units are (1) Brush: a compound object composed of bristles, (2) Stroke: a trajectory of position and pressure, (3) Dip: a description of the application of paint to a class of brushes, and (4) Paper: a mapping onto the display device. This modular system allows experimentation with various stochastic models of ink flow and color change. By selecting from a library of brushes, dips, and papers, the stroke can take on a wide variety of expressive textures.
Snap-dragging
Authors: Bier Eric A. , Stone Maureen C.
Published: November 2005

We are interested in the problem of making precise line drawings using interactive computer graphics. In precise line drawings, specific relationships are expected to hold between points and lines. In published interactive drawing systems, precise relationships have been achieved by using rectangular grids or by solving simultaneous equations (constraints). The availability of fast display hardware and plentiful computational power suggest that we should take another look at the ruler and compass techniques traditionally used by draftsmen. Snap-dragging uses the ruler and compass metaphor to help the user place his next point with precision, and uses heuristics to automatically place guiding lines and circles that are likely to help the user construct each shape. Snap-dragging also provides translation, rotation, and scaling operations that take advantage of the precision placement capability. We show that snap-dragging compares favorably in power and ease of use with grid or constraint techniques.
A multitasking switchboard approach to user interface management
Authors: Tanner Peter P. , MacKay Stephen A. , Stewart Darlene A. , Wein Marceli
Published: November 2005

A Switchboard model of user input management is presented which takes advantage of opportunities afforded by a multitasking multiprocessor programming environment. This model further separates application programming from the programming of the interaction dialogues as compared with conventional user interface management systems. It also provides powerful tools for implementing parallel forms of input, is suitable for managing interaction in window-based systems, and is very flexible.The paper describes this Switchboard model and its implementation on top of the Harmony operating system, as well as discussing some of the graphics support needed for the model.
An object-oriented user interface management system
Authors: Sibert John L. , Hurley William D. , Bleser Teresa W.
Published: November 2005

The George Washington User Interface Management System (GWUIMS) has been designed as a test bed for comparing user interface models, as a tool for rapidly prototyping highly interactive graphic user interfaces, and as a vehicle for investigating the applicability of knowledge-based technology to user interface design. The GWUIMS was designed and implemented using the object-oriented programming paradigm and consists of a variety of object classes representing different levels of abstraction, Responsibility for lexical, syntactic, and semantic levels of both input parsing and feedback are distributed throughout these classes. We include a description of the GWUIMS and a brief scenario to demonstrate its capabilities. A description of the implementation is followed by a discussion of the future application of knowledge representation techniques and the evolution towards an intelligent assistant for the user interface designer.
Adaptive precision in texture mapping
Authors: Glassner Andrew
Published: November 2005

We introduce an adaptive, iterative technique for obtaining texture samples of arbitrary precision when synthesizing a computer-generated image. The technique is an improvement on the sum table texturing method. To motivate the technique we analyze the error properties of the sum-table method. Based on that analysis we propose using a combination of tables independently or together to obtain a better estimate, and analyze the error properties of such methods. We then propose a new technique for obtaining texture samples whose accuracy is a function of the texture and the image. As part of this technique we propose the use of an auxiliary table which contains local estimates of the texture variance. We show how the iteration of a given sample may be controlled by values from this table. We then analyze the error in this method, and present images which demonstrate the improvement.
Anti-aliasing in topological color spaces
Authors: Turkowski Kenneth
Published: November 2005

The power of a color space to perform well in interpolation problems such as anti-aliasing and smooth-shading is dependent on the topology of the color space as well as the number of elements it contains.We develop the
Major-minor
color space, which has a topology and representation that lends itself to simple anti-aliasing computations between elements of an arbitrary set of colors in an inexpensive frame store.
Filtering by repeated integration
Authors: Heckbert Paul S.
Published: November 2005

Many applications of digital filtering require a space variant filter - one whose shape or size varies with position. The usual algorithm for such filters, direct convolution, is very costly for wide kernels. Image prefiltering provides an efficient alternative. We explore one prefiltering technique,
repeated integration
, which is a generalization of Crow's
summed area table
.We find that convolution of a signal with any piecewise polynomial kernel of degree
n
--1 can be computed by integrating the signal
n
times and point sampling it several times for each output sample. The use of second or higher order integration permits relatively high quality filtering. The advantage over direct convolution is that the cost of repeated integration filtering does not increase with filter width. Generalization to two-dimensional image filtering is straightforward. Implementations of the simple technique are presented in both preprocessing and stream processing styles.
An object-oriented library for hierarchical animation sequences
Authors: Gonzalez Ralph E.
Published: November 2005

A library for generating 3D graphics and animation sequences is presented, with the following features: (1) support for coordinated animation among arbitrarily-nested graphic segments, where animation may be specified with respect to an independent coordinate system within each nested segment; (2) support for time-based simulation; (3) support for multiple viewpoints and multiple display windows; (4) an object-oriented structure (using a "camera-projector" metaphor) providing an easy programming interface and extensibility; (5) encapsulation of machine-dependencies into alternative Screen classes, for portability among several platforms (presently Macintosh, PC-compatible, and X Window System). The library has been used by undergraduate students to program complex animation sequences. It presently supports only color 2D and 3D wireframe graphics, but may be extended to include light sources and rendering alternatives. The C++ source code has been placed in the public domain.
Introduction to the computer graphics reference model
Authors: Carson George S.
Published: November 2005

This is the final version of the introduction. It was prepared by the Computer Graphics Reference Model (CGRM) document editor based on comments on the previous version received from national bodies and decisions taken at the CGRM editing held in May 1992. National bodies are encouraged to give this document wide circulation.
Some perspectives on visual depth perception
Authors: Murray John
Published: November 2005

The process which people use to judge visually the relative and absolute distance of objects is quite complex and poorly understood, despite much investigation over a long period of time. However, one thing is clear--it's not simply a matter of triangulation using our two eyes; a variety of other factors seem to be brought into play with varying degrees of influence.Some psychologists believe that a wide variety of separate cues are taken into consideration when estimating distances. In this "constructionist" view, the various cues (which are used quite unconsciously) contribute independently to a mental "construction" process of perceived depth. Other researchers refute the entire concept of detecting depth specifically, preferring instead to incorporate it into a more general, dynamic mapping of the overall perceived scene. This latter viewpoint has become known as the "ecological approach" to visual perception.Many of the concepts are not new. Renaissance artists like Leonardo da Vinci were among the first to realize how depth could be rendered in two-dimensional paintings; they called it "artificial perspective." Since then, a great deal of work has gone into investigating this surprisingly complex topic, although much still remains to be done. However, it seems that some virtual reality developers and other computer graphics practitioners are unfamiliar with the terminology and the various existing concepts and knowledge in the field.The following review describes many of the principal depth cues, as understood by those adopting a constructionist viewpoint; it is followed by a short summary of the ecological approach. I hope this will assist those new to the field, and I offer my sincere apologies to others whose favorite concepts or definitions may have been poorly represented or, worse still, omitted entirely.