bluuebunny/crossref_metadata_2025 huggingface dataset:
The drawing prism
Authors: Greene Richard
Published: November 2005

Artists using conventional computer graphic input devices cannot produce the same visual effects which they can with traditional tools and media. The drawing prism is a new device which allows people to draw or paint directly into a frame buffer, using brushes, their hands, or a variety of other objects. These objects can be manipulated to achieve continuously adjustable line qualities and textures, in the same ways that artists have traditionally used their hands and tools.The device uses one face of a large transparent prisms as a drawing surface. A video camera views that surface from an angle such that it can only image the points of optical contact between drawing tools and the surface. These images are digitized and processed in real time so as to build up a drawing as the tools are moved along the surface. A layer of transparent liquid helps tools make optical contact with the drawing surface. Any light colored object can thus be used as a drawing tool.Details of the current implementation are provided along with suggestions for improving its resolution. Combinations of visual effects previously restricted to either traditional media or computer graphics are described and illustrated.
Geometric modeling of solid objects by using a face adjacency graph representation
Authors: Ansaldi Silvia , De Floriani Leila , Falcidieno Bianca
Published: November 2005

A relational graph structure based on a boundary representation of solid objects is described. In this structure, called face adjacency graph, nodes represent object faces, whereas edges and vertices are encoded into arcs and hyperarcs. Based on the face adjacency graph, we define a set of primitive face-oriented Euler operators, and a set of macrooperators for face manipulation, which allow a compact definition and an efficient updating of solid objects. We briefly describe a hierarchical graph structure based on the face adjacency graph, which provides a representation of an object at different levels of detail. Thus it is consistent with the stepwise refinement process through which the object description is produced.
Techniques for conic splines
Authors: Pratt Vaughan
Published: November 2005

A number of techniques are presented for making conic splines more effective for 2D computer graphics. We give a brief account of the theory of conic splines oriented to computer graphics. We make Pitteway's algorithm exact, and repair an "aliasing" problem that has plagued the algorithm since its introduction in 1967. The curvature-matching problem for conics is solved by way of a simple formula for curvature at an endpoint which permits curvature to be matched exactly at non-inflectior points and more closely than was previously realized possible at points of inflection. A formula for minimum-curvature-variation of conic splines is given. These techniques provide additional support for Pavlidis' position [6] that conics can often be very effective as splines.The work was motivated by, and provides much of the foundation for, an implementation of conic splines at Sun Microsystems as part of Sun's Pixrect graphics package, the lowest layer of Sun's graphics support.
Input/output linkage in a user interface management system
Authors: Olsen Dan R. , Dempsey Elizabeth P. , Rogge Roy
Published: November 2005

The GRaphical INteraction System (GRINS) is described, which integrates an automation-based dialogue controller with a dynamic display model to provide a User Interface Management System. The linkage between the logical device interface and the graphical presentation of virtual devices is discussed. A display manager to support dynamic manipulations of hierarchically structure images is presented. Lastly a model of Display Objects whereby application-specific display objects can have computational constraints defined is described. The constraint system is equivalent to an attributed grammar and is evaluated using an incremental attribute flow algorithm.
Squeak
Authors: Cardelli Luca , Pike Rob
Published: November 2005

Graphical user interfaces are difficult to implement because of the essential concurrency among multiple interaction devices, such as mice, buttons, and keyboards.
Squeak
is a user interface implementation language that exploits this concurrency rather than hiding it, helping the programmer to express interactions using multiple devices. We present the motivation, design and semantics of
squeak
. The language is based on concurrent programming constructs but can be compiled into a conventional sequential language; our implementation generates C code. We discuss how
squeak
programs can be integrated into a graphics system written in a conventional language to implement large but regular user interfaces, and close with a description of the formal semantics.
Issues and techniques in touch-sensitive tablet input
Authors: Buxton William , Hill Ralph , Rowley Peter
Published: November 2005

Touch-sensitive tablets and their use in human-computer interaction are discussed. It is shown that such devices have some important properties that differentiate them from other input devices (such as mice and joysticks). The analysis serves two purposes: (1) it sheds light on touch tablets, and (2) it demonstrates how other devices might be approached. Three specific distinctions between touch tablets and one button mice are drawn. These
concern the signaling of events, multiple point
sensing and the use of templates. These distinctions are reinforced, and possible uses of touch tablets are illustrated, in an example application. Potential enhancements to touch tablets and other input devices are discussed, as are some inherent problems. The paper concludes with recommendations for future work.
An automatic beautifier for drawings and illustrations
Authors: Pavlidis Theo , Van Wyk Christopher J.
Published: November 2005

We describe a method for inferring constraints that are desirable for a given (rough) drawing and then modifying the drawing to satisfy the constraints wherever possible. The method has been implemented as part of an online graphics editor running under the UNIX™ operating system and it has undergone modifications in response to user input. Although the framework we discuss is general, the current implementation is polygon-oriented. The relations examined are: approximate equality of the slope or length of sides, collinearity of sides, and vertical and horizontal alignment of points.
Parametric keyframe interpolation incorporating kinetic adjustment and phrasing control
Authors: Steketee Scott N. , Badler Norman I.
Published: November 2005

Parametric keyframing is a popular animation technique where values for parameters which control the position, orientation, size, and shape of modeled objects are determined at key times, then interpolated for smooth animation. Typically the parameter values defined by the keyframes are interpolated by spline techniques with the result that the parameter change
kinetics
are implicitly defined by the given keyframe times and data points. Existing interpolation systems for animation are examined and found to lack certain desirable features such as continuity of acceleration or convenient kinetic control. The requirements of interpolation for animation are analyzed in order to determine the characteristics of a satisfactory system. A new interpolation system is developed and implemented which incorporates second-derivative continuity (continuity of acceleration), local control, convenient kinetic control, and joining and phrasing of successive motions. Phrasing control includes the ability to parametrically control the degree and extent of smooth motion flow between separately defined motions.
Construction of fractal objects with iterated function systems
Authors: Demko Stephen , Hodges Laurie , Naylor Bruce
Published: November 2005

In computer graphics, geometric modeling of complex objects is a difficult process. An important class of complex objects arise from natural phenomena: trees, plants, clouds, mountains, etc. Researchers are at present investigating a variety of techniques for extending modeling capabilities to include these as well as other classes. One mathematical concept that appears to have significant potential for this is fractals. Much interest currently exists in the general scientific community in using fractals as a model of complex natural phenomena. However, only a few methods for generating fractal sets are known. We have been involved in the development of a new approach to computing fractals. Any set of linear maps (affine transformations) and an associated set of probabilities determines an Iterated Function System (IFS). Each IFS has a unique "attractor" which is typically a fractal set (object). Specification of only a few maps can produce very complicated objects. Design of fractal objects is made relatively simple and intuitive by the discovery of an important mathematical property relating the fractal sets to the IFS. The method also provides the possibility of solving the inverse problem. given the geometry of an object, determine an IFS that will (approximately) generate that geometry. This paper presents the application of the theory of IFS to geometric modeling.
An image synthesizer
Authors: Perlin Ken
Published: November 2005

We introduce the concept of a Pixel Stream Editor. This forms the basis for an interactive synthesizer for designing highly realistic Computer Generated Imagery. The designer works in an interactive Very High Level programming environment which provides a very fast concept/implement/view iteration cycle.Naturalistic visual complexity is built up by composition of non-linear functions, as opposed to the more conventional texture mapping or growth model algorithms. Powerful primitives are included for creating controlled stochastic effects. We introduce the concept of "solid texture" to the field of CGI.We have used this system to create very convincing representations of clouds, fire, water, stars, marble, wood, rock, soap films and crystal. The algorithms created with this paradigm are generally extremely fast, highly realistic, and asynchronously parallelizable at the pixel level.
Visual simulation of clouds
Authors: Gardner Geoffrey Y.
Published: November 2005

Clouds present serious problems to standard computer image generation techniques because clouds do not have well-defined surfaces and boundaries. In addition, clouds contain varying degrees of translucence, and their amorphous structure can change with time. Although several approaches to cloud simulation have produced impressive results, they have relied on complex mathematical models which produce high computation costs for a single image.This paper describes a new approach to cloud simulation using simple planar and curved surfaces whose surface shading and translucence are modulated by a mathematical texturing function. This approach represents the appearance of clouds with enough realism for a wide range of visual simulation but does so at a reasonable computational cost, allowing the generation of sequences of images on small minicomputers. In addition, the cloud model can be constructed in a straightforward manner.
The University of Alberta user interface management system
Authors: Green Mark
Published: November 2005

In this paper the design and implementation of the University of Alberta user interface management system (UIMS) is discussed. This UIMS is based on the Seeheim model of user interfaces, which divides the user interface into three separate components. The Seeheim model of user interfaces is discussed along with its relationship to the design of UIMSs. The techniques used to design the three user interface components are briefly presented. A mixture of interactive and written notations are used in the design of the user interface. Some interesting features of this UIMS are interactive screen and menu layout, support for three dialogue notations, flexible interface to the application program, ability to adapt to different users, and the use of concurrent processes in user interface implementation The techniques used in the implementation of this UIMS are discussed.
From range scans to 3D models
Authors: Curless Brian
Published: November 2005

Each year, we see a growing number of 3D range scanning products on the SIGGRAPH exhibition floor. You may find yourself asking "how do these technologies work?" and "how can I make use of the shape data they produce?" In this article, I will describe a few of the more common range scanning technologies. Then, I will step through a pipeline that takes the range data into a single geometric model and will conclude with a discussion of the future of range scanning.
Summer meeting produces results
Authors: Carson George S.
Published: November 2005

This edition of the Standards Pipeline reports on the results of the JTC I/ SC 24 (Computer Graphics and Image Processing) standards committee meeting held this summer in Korea. This report is divided into several sections:1. SC 24 as a whole2. Synthetic Environments Study Group3. Archiving and Distribution Study Group4. Interaction Study Group5. Working Group 6 (Multimedia Presentation and Interchange)5.1 3D and the Web5.2 CGM and the Web5.3 Portable Network Graphics (PNG)6. Working Group 7 (Image Processing and Interchange)For more information about the work of SC 24 you can visit the committee's website at
http://www.bsi.org.uk/sc24/.
ACM SIGGRAPH outreach to the computer games community
Authors: Rhyne Theresa-Maria
Published: November 2005

As noted in
Computer Graphics
34(1) February 2000, ACM SIGGRAPH began the year 2000 with a new special project to outreach to the computer games community. So far, we have received a terrific number of emails from computer games professionals and other interested folks. Simultaneously, the SIGGRAPH 2000 Courses Committee accepted an innovative course entitled: "Games Research: the Science of Interactive Entertainment," Craig Reynolds of Sony Computer Entertainment America and Chris Hecker of definition six, inc. are the course organizers. Please see:
http://www.siggraph.org/s2000/conference/courses/crs39.html.
As part of this SIGGRAPH outreach effort, the CMP Game Media Group provided me a warm welcome at the Game Developers Conference 2000. Below is the report of my adventures.
Universal media
Authors: Walsh Aaron E.
Published: November 2005

Universal Media is a Web3D consortium working group solution that increases the realism of on-line Web3D worlds (VRML, Java 3D and other on-line 3D technologies). It also decreases network downloads by defining a small, cross-platform library of locally resident media elements (textures, sounds, 3D objects and filters) and a uniform resource name (URN) mechanism by which Web3D content creators can incorporate these media elements into their worlds. Universal Media allows content authors to create media-rich worlds that can be instantly loaded over even the slowest dial-up modem Internet connections. Fully compatible with standard VRML browsers, Universal Media conforms to the VRML97 specification, allowing media-rich worlds to load 20 to 50 times faster on average without deviating from industry standards.Because Universal Media is stored on the user's hard drive (or other local storage), content authors can use Universal Media just as they do local resources, without concern for downloading each media element over a network connection. This simple but powerful concept allows multi-megabyte, media-rich worlds such as the one illustrated in Figure 1 to load almost instantly over even the slowest network connections.In this respect, Universal Media can be thought of as a locally resident suite of 3D media primitives, or media building blocks, that enable Web3D content developers to construct realistic looking and sounding worlds without the penalty of network transfers typically associated with media-rich worlds. And, since the media elements that ultimately make up the Universal Media library are expected to be of extremely high quality, Web3D content developers will be able to build compelling worlds in considerably less time and at an overall lower cost than if they were to create such media themselves.Specifically, the Web3D Consortium's Universal Media Working Group (
http://www.web3d.org/Working-Groups/media/
mirrored at
http://www.web3dmedia.com/
) is defining cross-platform media libraries comprised of textures, sounds and 3D objects that reside on the client (end-user) computer systems. In addition, the Universal Media Working Group is defining a standard media filter mechanism that allows such content to be dynamically transformed using predefined, yet customizable, filters (a morph filter might dynamically morph the geometry of a 3D cat object into a lion, for example, while a ripple filter might animate a grass texture so that it appears to ripple in the wind).Universal Media is distributed freely through the Web3D Consortium. At the time of this writing, version 1.0 of the Textures library (Textures 1.0) has been released, while sounds and 3D objects are scheduled for release in mid-2000. Universal Media filters are currently under development, and the first library of pre-made filters is expected to ship in late 2000.
Chapters continue to grow
Authors: Lang Scott
Published: November 2005

Scott Langs's spell as Director for Professional Chapters recently ended, but his legacy will live on in a strong organisation that is immensely popular, thanks in great part to the remarkable job Scott has been doing for the past five years. He has influenced not only the chapters, but also so many other aspects of SIGGRAPH life, and his leadership, generosity and commitment have served as tremendous examples to others involved in the organisation. I've benefited from his wisdom and help, and I wish him all the best in his future endeavours, and look forward to working with him again at some point in the future!Colleen Cleary will take on the responsibilities as Director for both the Professional and Student Chapters, and I know that she will do a tremendous job in not only continuing where Scott left off, but in making the position truly her own!Colleen suggested that it would be fitting to reprint Scott's farewell email in addition to the regular Chapters content, and I wholeheartedly agreed. You'll find this plus Colleen's reply, the annual Chapters report and most recent update below.
An open discussion on public policy
Authors: Ellis Bob
Published: November 2005

As usual, the column is multi-topic. It starts with a brief review of the SIGGRAPH Public Policy Program. This is followed with some comments (and my responses) on the program raised by an interested SIGGRAPH member. Once again, Myles Losch presents recent information on digital copy protection, including its potential application to free terrestrial broadcast digital TV. We provide a review of the 2000 edition of one of the most important conferences at the intersection of competing and public policy, the ACM sponsored Computers, Freedom and Privacy Conference (CFP). And finally, we describe the availability of our third on-line survey.
A muscle model for animation three-dimensional facial expression
Authors: Waters Keith
Published: November 2005

The development of a parameterized facial muscle process, that incorporates the use of a model to create realistic facial animation is described.Existing methods of facial parameterization have the inherent problem of hard-wiring performable actions. The development of a muscle process that is controllable by a limited number of parameters and is non-specific to facial topology allows a richer vocabulary and a more general approach to the modelling of the primary facial expressions.A brief discussion of facial structure is given, from which a method for a simple modelling of a muscle process that is suitable for the animation of a number of divergent facial types is described.
Flocks, herds and schools: A distributed behavioral model
Authors: Reynolds Craig W.
Published: November 2005

The aggregate motion of a flock of birds, a herd of land animals, or a school of fish is a beautiful and familiar part of the natural world. But this type of complex motion is rarely seen in computer animation. This paper explores an approach based on simulation as an alternative to scripting the paths of each bird individually. The simulated flock is an elaboration of a particle systems, with the simulated birds being the particles. The aggregate motion of the simulated flock is created by a distributed behavioral model much like that at work in a natural flock; the birds choose their own course. Each simulated bird is implemented as an independent actor that navigates according to its local perception of the dynamic environment, the laws of simulated physics that rule its motion, and a set of behaviors programmed into it by the "animator." The aggregate motion of the simulated flock is the result of the dense interaction of the relatively simple behaviors of the individual simulated birds.
Principles and applications of pencil tracing
Authors: Shinya Mikio , Takahashi T. , Naito Seiichiro
Published: November 2005

Pencil tracing, a new approach to ray tracing, is introduced for faster image synthesis with more physical fidelity. The paraxial approximation theory for efficiently tracing a pencil of rays is described and analysis of its errors is conducted to insure the accuracy required for pencil tracing. The paraxial approimation is formulated from a 4x4 matrix (a system matrix) that provides the basis for pencil tracing and a variety of ray tracing techniques, such as beam tracing, ray tracing with cones, ray-object intersection tolerance, and a lighting model for reflection and refraction. In the error analysis, functions that estimate approximation errors and determine a constraint on the spread angle of a pencil are given.The theory results in the following fast ray tracing algorithms; ray tracing using a system matrix, ray interpolation, and extended 'beam tracing' using a 'generalized perspective transform'. Some experiments are described to show their advantages. A lighting model is also developed to calculate the illuminance for refracted and reflected light.
Ray tracing Jell-O
®
Brand Gelatin
Authors: Heckbert Paul S.
Published: November 2005

Ray tracing has established itself in recent years as the most general image synthesis algorithm. Researchers have investigated ray-surface intersection calculations for a number of surface primitives, including checkerboards, glass balls, green fractal
hills, mandrills, abstract blue surfaces
, more glass balls, robot arms, pool balls, low-resolution clouds, morphine molecules, aquatic blobby things making strange noises, fantastic cities, and running skeletons. Unfortunately,
nobody has ray traced any food
. The
Dessert Realism Project
here at Pixar is addressing this problem. This paper presents new technology for ray tracing Jell-O® brand gelatin. We believe the method may have application to other brands of gelatin and perhaps pudding as well.
GRAPE: An environment to build display processes
Authors: Nadas Tom , Fournier Alain
Published: November 2005

New modelling primitives and new rendering techniques are appearing at a rapid rate. To be able to implement and evaluate them easily, we need a very flexible display environment. We describe an environment which allows experimenting both with the basic modelling and rendering operations and with the process structure of the display system.The desired operations are implemented in
nodes
, coded in a traditional programming language, which can then be structured into arbitrary directed acyclic graphs. These nodes are all "plug compatible", and pass streams of
appels
, which are generalized pixels, that is data structures containing information necessary for pixel evaluation. In addition, synchronization parameters are used to allow the expansion or the reduction of the stream of appels.This approach allows the assembly of new display systems from existing modules without coding, making it easy to experiment with different architectures and display processes. Algorithm designers are also able to test an algorithm at any point of the display process with a minimum of new coding.We describe an implementation of the scheme with a library of nodes written in C and the assembly of the graphs made through the use of the directory manipulation tools provided under UNIX™. We give examples of the uses of the implementation to build basic nodes, variations in compositing and texture mapping and special-purpose display systems.
The Reyes image rendering architecture
Authors: Cook Robert L. , Carpenter Loren , Catmull Edwin
Published: November 2005

An architecture is presented for fast high-quality rendering of complex images. All objects are reduced to common world-space geometric entities called micropolygons, and all of the shading and visibility calculations operate on these micropolygons. Each type of calculation is performed in a coordinate system that is natural for that type of calculation. Micropolygons are created and textured in the local coordinate sysem of the object, with the result that texture filtering is simplified and improved. Visibility is calculated in screen space using stochastic point sampling with a z buffer. There are no clipping or inverse perspective calculations. Geometric and texture locality are exploited to minimize paging and to support models that contain arbitrarily many primitives.
Accurate triangulations of deformed, intersecting surfaces
Authors: Von Herzen Brian , Barr Alan H.
Published: November 2005

A quadtree algorithm is developed to triangulate deformed, intersecting parametric surfaces. The biggest problem with adaptive sampling is to guarantee that the triangulation is accurate within a given tolerance. A new method guarantees the accuracy of the triangulation, given a "Lipschitz" condition on the surface definition. The method constructs a hierarchical set of bounding volumes for the surface, useful for ray tracing and solid modeling operations. The task of adaptively sampling a surface is broken into two parts: a subdivision mechanism for recursively subdividing a surface, and a set of subdivision criteria for controlling the subdivision process.An adaptive sampling technique is said to be robust if it accurately represents the surface being sampled. A new type of quadtree, called a
restricted quadtree
, is more robust than the traditional unrestricted quadtree at adaptive sampling of parametric surfaces. Each sub-region in the quadtree is half the width of the previous region. The restricted quadtree requires that adjacent regions be the same width within a factor of two, while the traditional quadtree makes no restriction on neighbor width. Restricted surface quadtrees are effective at recursively sampling a parametric surface. Quadtree samples are concentrated in regions of high curvature, and along intersection boundaries, using several subdivision criteria. Silhouette subdivision improves the accuracy of the silhouette boundary when a viewing transformation is available at sampling time. The adaptive sampling method is more robust than uniform sampling, and can be more efficient at rendering deformed, intersecting parametric surfaces.
Adaptive forward differencing for rendering curves and surfaces
Authors: Lien Sheue-Ling , Shantz Michael , Pratt Vaughan
Published: November 2005

An adaptive forward differencing algorithm is presented for rapid rendering of cubic curves and bicubic surfaces. This method adjusts the forward difference step size so that approximately one pixel is generated along an ordinary or rational cubic curve for each forward difference step. The adjustment involves a simple linear transformation on the coefficients of the curve which can be accomplished with shifts and adds. This technique combines the advantages of traditional forward differencing and adaptive subdivision. A hardware implementation approach is described including the adaptive control of a forward difference engine. Surfaces are rendered by drawing many curves spaced closely enough together so that no pixels are left unpainted. A simple curve anti-aliasing algorithm is also presented in this paper. Anti-aliasing cubic curves is supported via tangent vector output at each forward difference step. The adaptive forward differencing algorithm is also suitable for software implementation.
Boundary evaluation of non-convex primitives to produce parametric trimmed surfaces
Authors: Crocker Gary A. , Reinke William F.
Published: November 2005

To integrate a CSG-based solid modeler into an existing wireframe/surface modeling system, new boundary evaluation technology has been developed. This scheme uses exact representations for the simple quadric surfaces and both exact and approximate representations of higher-order curved surfaces. It supports parametric primitives (box, wedge, sphere, cylinder, cone, torus), procedural primitives (extrusion, revolution, tube) and a sculptured surface primitive. The output includes curves, parametric trimmed surfaces, and a data structure of adjacency information.An existing boundary evaluator (PADL-2's) has been enhanced to allow a general non-convex faceted primitive with planar and quadric facets. This new hybrid evaluator combines two techniques for curve/primitive classification. PADL-2's existing halfspace-based classification is reserved for the simple convex primitives, and a new ray firing based classification is applied to the non-convex primitives. After evaluation, approximate intersection curves (from intersections involving higher order surfaces) are refined to a specified tolerance by exploiting an exact parametric representation of the surfaces of the primitives. The refined curves and the quadric surface intersection curves are used to create a parametric trimmed surface representation of the solid. This combination of techniques and representations offers advantages in accuracy, robustness and efficiency suitable to a production environment.
Direct least-squares fitting of algebraic surfaces
Authors: Pratt Vaughan
Published: November 2005

In the course of developing a system for fitting smooth curves to camera input we have developed several direct (i.e. noniterative) methods for fitting a shape (line, circle, conic, cubic, plane, sphere, quadric, etc.) to a set of points, namely exact fit, simple fit, spherical fit, and blend fit. These methods are all dimension-independent, being just as suitable for 3D surfaces as for the 2D curves they were originally developed for.Exact fit generalizes to arbitrary shapes (in the sense of the term defined in this paper) the well-known determinant method for planar exact fit. Simple fit is a naive reduction of the general overconstrained case to the exact case. Spherical fit takes advantage of a special property of circles and spheres that permits robust fitting; no prior direct circle fitters have been as robust, and there have been no previous sphere fitters. Blend fit finds the best fit to a set of points of a useful generalization of Middleditch-Sears blending curves and surfaces, via a nonpolynomial generalization of planar fit.These methods all require (
am
+
bn
)
n
2
operations for fitting a surface of order
n
to
m
points, with
a
= 2 and
b
= 1/3 typically, except for spherical fit where
b
is larger due to the need to extract eigenvectors. All these methods save simple fit achieve a robustness previously attained by direct algorithms only for fitting planes. All admit incremental batched addition and deletion of points at cost
an
2
per point and
bn
3
per batch.
Shading bicubic patches
Authors: Shantz Michael , Lien Sheue-Ling
Published: November 2005

We present several techniques for implementing Phong shading in hardware for bicubic patches. Patches are shaded, not by subdividing into polygons, but by drawing many curves close together leaving no pixel gaps. Each curve is drawn using an adaptive forward difference algorithm which generates the coordinates as well as the shading parameters as cubic functions incrementally evaluated along the curve. The forward difference step size is adaptively adjusted so that it generates approximately one pixel along the curve per forward difference step. The hardware implements Phong shading directly with a surprisingly simple configuration built from general purpose compute units and look-up tables. Two new methods are presented for deriving bicubic approximations to the shading parameters over a bicubic patch. One method uses two Coons patches to approximate the unnormalized
N·L
, and
N·H
, and a third Coons patch for
N·N
, where
N
is the surface normal,
L
is the light direction, and
H
is the direction of maximum highlight. In this case the hardware performs the normalization per pixel. The second method uses two Coons patches to approximate the normalized dot products
N·L
, and
N·H.
The method is suitable for both hardware and software implementations.
A parallel processor architecture for graphics arithmetic operations
Authors: Torborg John G.
Published: November 2005

Interactive 3D graphics applications require significant arithmetic processing to handle complex models, particularly if realistic rendering techniques are used. Current semiconductor technology cannot provide the necessary performance without some form of multi-processing.This paper describes a graphics processor architecture which can be configured with an arbitrary number of identical processors operating in parallel. Each of the parallel processors can be programmed identically as if it were a single processor system, substantially simplifying software development and allowing complex rendering functions to take advantage of the multiple processors. The architecture described is able to achieve extremely high performance while allowing the price/performance of the system to be optimized for a given application.Techniques are described for handling graphics command distribution, sequencing of commands which must be processed in order, parallel processing of graphics primitive picking, and handling inquiry (read-back) commands.
Energy constraints on parameterized models
Authors: Witkin Andrew , Fleischer Kurt , Barr Alan
Published: November 2005

A simple but general approach to imposing and solving geometric constraints on parameterized models is introduced, applicable to animation as well as model construction. Constraints are expressed as energy functions, and the energy gradient followed through the model's parameter space. Intuitively, energy constraints behave like forces that pull and parametrically deform the parts of the model into place. A wide variety of geometric constraints are amenable to this formulation, and may be used to influence arbitrary model parameters. A catalogue of basic constraints is presented, and results are shown.
Rectangular convolution for fast filtering of characters
Authors: Naiman Avi , Fournier Alain
Published: November 2005

While the race towards higher-resolution bitmap displays is still on, many grayscale displays have appeared on the scene. To fully utilize their capabilities, grayscale fonts are needed, and these can be produced by filtering bi-level masters. Most of the efficient filtering techniques cannot directly be applied. For example, prefiltering is impractical, due to the number of character masters and the requirement of sub-pixel positioning. Furthermore, we would like to impose as few restrictions as possible on the characteristics of the filter, in order to facilitate exploration into the quality of various filters.We describe a fast filtering technique especially adapted to this task. The characters are decomposed into rectangles, and a summed-area representation of the filter is efficiently convolved with each individual rectangle to construct the grayscale character. For a given filter, the number of operations is
O (linear size of the grayscale character)
, which is optimal.We give an analysis of the efficiency of this technique, and examples of its implementation applied to various families of fonts and point sizes. The performance of the implementation is such that filtering characters for grayscale displays is feasible in realtime on personal workstations.
Character generation under grid constraints
Authors: Hersch Roger D.
Published: November 2005

An original and fast filling algorithm based on vertical scan line sweep and contour tracking of a presorted shape description allows filling of character shapes with real subpixel resolution. Identical parts of a character lying at a different phase in respect to the grid will have a dissimilar discrete look. Grid constraints are applied in order to force given parts of a character (stems, serifs) to attain identical phasing. So that several contraints may be applied, degrees of freedom are provided in the form of stretchable null-segments inserted at particular locations in the character outline description. Grid constraints are also applied to avoid discrete arcs with an isolated pixel or a long horizontal or vertical run. The type of constraints applied to parts of a character consists only of horizontal or vertical subpixel translations. The resulting character description therefore remains nearly identical to the original description. The processing time used to apply grid constraints is negligible, compared with the time needed for character scan-conversion and filling. Hence, this method is very well adapted for direct character generation on non-impact printers. It is also suitable for character rasterization in typographic computer-aided design systems.
Planar 2-pass texture mapping and warping
Authors: Smith Alvy Ray
Published: November 2005

The 2-pass tranformation replaces a 2-D (2-dimensional) transformation with a sequence of orthogonal, simpler 1-D transformation. It may be used for the closely related processes of texture mapping and warping in computer graphics and image processing. First, texture maps onto planar quadric and superquadric surfaces and, second, planar bicubic and biquadratic warps of images are shown to be 2-pass transformable. A distinction between serial and parallel warps is introduced to solve a confusion in terms between computer graphics and image processing. It is shown that an
n
-th order serial polynomial warp is equivalent to an (
n
2
+
n
)-th order parallel polynomial warp. It is also shown that the serial equivalent to a parallel polynomial warp is generally not a polynomial warp, being more complicated than a polynomial. The unusual problem of bottlenecking and the usual one of antialiasing are discussed in the 2-pass context.
Bidirectional reflection functions from surface bump maps
Authors: Cabral Brian , Max Nelson , Springmeyer Rebecca
Published: November 2005

The Torrance-Sparrow model for calculating bidirectional reflection functions contains a geometrical attenuation factor to account for shadowing and occlusions in a hypothetical distribution of grooves on a rough surface. Using an efficient table-based method for determining the shadows and occlusions, we calculate the geometric attenuation factor for surfaces defined by a specific table of bump heights.Diffuse and glossy specular reflection of the environment can be handled in a unified manner by using an integral of the bidirectional reflection function times the environmental illumination, over the hemisphere of solid angle above a surface. We present a method of estimating the integral, by expanding the bidirectional reflection coefficient in spherical harmonics, and show how the coefficients in this expansion can be determined efficiently by reorganizing our geometric attenuation calculation.
The zonal method for calculating light intensities in the presence of a participating medium
Authors: Rushmeier Holly E. , Torrance Kenneth E.
Published: November 2005

The zonal method for calculating radiative transfer in the presence of a participating medium is applied to the generation of realistic synthetic images. The method generalizes the radiosity method and allows for emission, scattering, and absorption by a participating medium. The zonal method accounts for volume/surface interactions which have not been previously included, as well as volume/volume and surface/surface interactions. In addition, new algorithms, based on the hemi-cube formulation, are introduced for calculating the geometric factors required by the zonal method.
A shading model for atmospheric scattering considering luminous intensity distribution of light sources
Authors: Nishita Tomoyuki , Miyawaki Yasuhiro , Nakamae Eihachiro
Published: November 2005

Studio spotlights produce dazzling shafts of light, while light scattered from fog illuminated by automobile headlights renders driving difficult. This is because the particles in the illuminated volume become visible by scattering light. A shading model for scattering and absorption of light caused by particles in the atmosphere is proposed in this paper. The method takes into account luminous intensity distribution of light sources, shadows due to obstacles, and density of particles. The intensity at a viewpoint is calculated by integration of light scattered by particles between the viewpoint and a given point on an object. The regions to be treated in this manner are localized by considering illumination volumes and shadow volumes caused by obstacles in the illumination volumes.
Graphics goodies #1—a filling algorithm for arbitrary regions
Authors: Lind Bernd , Hrycej Tomas
Published: November 2005

A boundary-defined filling algorithm for arbitrary regions and filling patterns is presented. It has the completeness property of Shani's graph-based algorithm, but avoids the necessity of drawing additional "blocking lines" between the cycle-sensitive subregions.
MIT educators share success
Authors: Belcher John W. , Bessette R. Mark
Published: November 2005

This column describes the use of computer graphics as a teaching tool. At MIT, the course Physics 8.02 has a high enrollment, but it is one of the more difficult classes for students because of the non-intuitive nature of electromagnetism. In order to properly demonstrate the phenomena, Professor John Belcher developed a series of short videos with animation and text of selected experiments. He emphasizes that "the power of animation in explaining electromagnetism can only be appreciated by viewing sample animations." You can find examples of these animations at
http://web.mit.edu/jbelcher/www/anim.html
This article is reprinted from the SIGGRAPH 2000 Educators Program.
Computer graphics education directory
Authors: Cunningham Steve
Published: November 2005

This is SIGGRAPH's second directory of college-level computer graphics education, covering courses in computer graphics in a broad spectrum of disciplines. This directory is a single source of computer graphics course information. If you are a student entering college or considering a change of studies, a professional considering broadening your skills, or an educator seeking broader contacts in graphics among your peers, this directory is designed for you.The directory was compiled from the first directory and responses to a questionnaire sent out last spring. These responses were divided up by topic according to information received on the questionnaire and our perception of the course's audience. The placement of some courses may not be precise, so you may be advised to use more than one directory list in your search. For example, someone interested in graphics for architects would consult the Arts, Architecture, and Design listings, but might also find useful information in the list on Engineering, CAD/CAM, and Drafting. All interesting entries should be followed up by direct contact with the school for the many details of schedule, cost, and admission which are not included here.The courses we received were placed in individual lists by the following criteria. The Concepts and Systems list consists of courses covering general concepts in computer graphics and systems for producing graphics; such courses are often found in Computer Science or EECS programs and have no particular application orientation. The Engineering, CAD/CAM, and Drafting list contains courses which seem to be oriented toward applications in these areas. For CAD/CAM and Drafting courses, this is rather easy to tell, while the engineering orientation is inferred from a location in an Engineering program with no other information, or from a title such as "Engineering Computer Graphics." Many Engineering programs, however, have courses which seem to fit the Concepts and Systems category most closely and so are listed there. The other lists are fairly easily categorized, except for some problems determining where to place courses in Design; here the home program is usually the determining factor.
Computer graphic standards
Authors: Meads Jon
Published: November 2005

SIGGRAPH has a long history of involvement with standards. But since the great Core vs. GKS debate, there has been little reported on computer graphics standards activities in Computer Graphics, even though SIGGRAPH has been an active member of X3's Technical Committee on Computer Graphics (X3113).As SIGGRAPH's new principal representative to X3H3, I have agreed to provide an article for each issue of Computer Graphics, with the exception ofthe issue containing the SIGGRAPH conference proceedings. These articles are intended to be both informative and provocative. I'll try to keep you informed of the developments going on in regard to computer graphics standards, explain the rationale offered for various decisions and will provide opinions, mine and others.In addition, I will be glad to respond to questions, concerns and comments from you. Please send correspondence to Jon Meads, Jon Meads & Associates, 2516 N E 19th Avenue, Portland, OR 97212.
An efficient algorithm for finding the CSG representation of a simple polygon
Authors: Dobkin David , Guibas Leonidas , Hershberger John , Snoeyink Jack
Published: November 2005

We consider the problem of converting boundary representations of polyhedral objects into constructive-solid-geometry (CSG) representations. The CSG representations for a polyhedron
P
are based on the half-spaces supporting the faces of
P
. For certain kinds of polyhedra this problem is equivalent to the corresponding problem for simple polygons in the plane. We give a new proof that the interior of each simple polygon can be represented by a monotone boolean formula based on the half-planes supporting the sides of the polygon and using each such half-plane only once. Our main contribution is an efficient and practical
O(n
log
n
) algorithm for doing this boundary-to-CSG conversion for a simple polygon of
n
sides. We also prove that such nice formulæ do not always exist for general polyhedra in three dimensions.
A new radiosity approach by procedural refinements for realistic image sythesis
Authors: Shao Min-Zhi , Peng Qun-Sheng , Liang You-Dong
Published: November 2005

According to the rendering equation, the diffuse and the specular components of the outgoing intensity of each surface patch should be solved simultaneously. Rather than establishing a huge set of linear equations defining the unknown directional intensities for all directions and all surface patches, we expand the concept of the delta form-factor which concerns the light energy transfer of a surface patch along a respective direction. As the delta form-factor for non-diffuse surface patches are dependent on the spatial and spectral distributions of light energy, they could not be calculated geometrically. In this paper, we present a new radiosity approach which progressively approximates the delta form-factors and the light energy distributions within a general environment to the correct solution. The nucleus of our approach is procedural iteration. Statistics indicate the potentials of this method for complex non-diffuse environments.