EG1990 Proceedings (Technical Papers)

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Shading and Shadowing with Linear Light Sources
(Eurographics Association, 1990) Poulin, Pierre; Amanatides, John
In virtually all rendering systems, linear light sources are modeled with a series of point light sources that require considerable computing resources to produce realistic looking results. A general solution for shading surfaces illuminated by a linear light source is proposed. A formulation allowing for faster computation of the diffuse component of light reflection is derived. By assuming Phong's specular component, simple, inexpensive and convincing results are produced with the use of a Chebyshev approximation. A shadowing algorithm is also presented. As shadowing from linear light sources is expensive, two acceleration schemes, extended from ray tracing, are evaluated.
HYPERIMAGES - AN ALTERNATIVE TO THE CONVENTIONAL DIGITAL IMAGES
(Eurographics Association, 1990) Bieri, Hanspeter
Hyperimages represent a variation of the conventional digital images which implies pixels of different dimensions within the same image. The extent of a hyperimage is the disjoint union of all pixel extents it contains, which are relatively open unit cubes with respect to the euclidean topology of the underlying space. This approach is independent of any specific dimension of image and space, respectively, and allows strict partitioning of images into subimages, not just subdividing. The applicability of hyperimages is illustrated by a number of algorithms useful in image analysis.
Mathematical Models for Semi-globalized Spectral Synthesis
(Eurographics Association, 1990) Anjyo, Ken-ichi
Semi-globalized spectral synthesis is proposed as a new tool for three-dimensional scene description consisting of many natural objects, such as terrain, sea waves, and clouds. The method is based on the mathematical theory of spectral representation of stochastic processes. In this paper, mathematical models in the method are presented under rigorous formulation and then their stochastic properties are shown. Some simple techniques for practical improvements of the original models in depicting scenes are also explained along with the examples obtained.
END USER PROGRAMMING ENVIRONMENTS : INTERACTIVE PROGRAMMING-ON-EXAMPLE IN CAD PARAMETRIC DESIGN
(Eurographics Association, 1990) Girard, P.; Pierra, G.; Guittet, L.
In recent years, the number of computer end-users who do not know programming has increased rapidly. This new phenomenon has spurred a great deal of research about program design using very different approaches from the usual methods, which, as is well known, are very difficult to learn [1]. This research has touched on many programming fields : physical system simulation [2], graphical interface tailoring [3] and "macros" implementation [4] [5], data base access [6], lessons programming in Computer Aided Teaching [1] ... B.A. Myers [7] suggests a useful taxonomy for classifying these different systems. The three orthogonal criteria he uses define eight categories. A system is much more suitable for end-user programming when it is : - interactive, i.e. able to quickly echo the effect of one step of program designing, - graphic, or visual, i.e. allowing program design by commands working (at least) on a bi-dimensional environment, - associated with a running example, i.e. program designing uses values representing a running example of the program. The goal of this paper is twofold. On the one hand, it looks at a domain, rarely quoted in synthetic reviews [6] [7] [4], where these techniques are often used efficiently, and where end-user programming goes beyond the experimental phase : we are referring to parametric-design in Computer Aided Design (CAD). On the other hand, it presents a graphical interactive programming-on-examples system, named LIKE, which removes most of the problems pointed out by recent studies [7] [5].
3D MODELLING AND MOTION OF DEFORMABLE SOLIDS FROM 2D IMAGES
(Eurographics Association, 1990) Neveu, Marc; Faudot, Dominique
Our work purpose is to elaborate a geometric and motional model for deformable solids, known only by a very small number of general crosssections images. We start from a generic 3D model of the studied solid we distort according to detected boundaries in the above mentioned images. To give the solid motion model, our work uses moving point constraints and inbetweening methods on an image sequence : we select keyframes on which we interpolate characteristic points. Then we use Coons patches to compute the inbetween frames and realize an animation? On an echocardiographic application, we obtained good results in the model precision and detected edges by image processing similar to cardiologists' hand drawn edges. Besides, the model distortion, characteristic points tracking and 2D motion simulation are encouraging, although improvements are necessary.
TRIMO A Workstation-Based Interactive System for the Generation, Manipulation, and Display of Surfaces over Arbitrary Topological Meshes
(Eurographics Association, 1990) Slusallek, Philipp B.; Seidel, Hans-Peter
TRIMO has been designed as a workstation-based interactive system for the generation, manipulation, and display of surfaces over arbitrary toplogical meshes. In addition to rational tensor product Bezier and B-spline surfaces, TRIMO also supports piecewise rational triangular Bezier and B-patch surfaces. TRIMO has been implemented in C++ under the X Window System. Special emphasis has been given to a hierarchical data structure and to a menu-and-mouse-driven hierarchical user interface.
Hemi-Cube Ray-Tracing: A Method for Generating Soft Shadows
(Eurographics Association, 1990) Meyer, Urs
This paper presents a new ray-tracing technique for generating soft shadows. The technique treats scenes consisting of light sources and opaque objects which are polygons or polyhedra of arbitrary shape and size. To determine the intensity at a point on a surface, the hemisphere is sampled extensively through the use of hemi-cubes. So-called item-buffer boxes, a combination of itembuffers and buffer boxes, are used to calculate ray intersections as well as to suppress image aliasing. Several methods for reducing aliasing caused by hemi-cubes are discussed. The uniform treatment of rays allows for a straightforward extension of the algorithm to produce fuzzy reflections. The success of the new technique depends on a fast implementation of a visible surface algorithm as provided by today’s high-end graphics workstations. The results are images of realistically illuminated synthetic environments.
PRELOG - A SYSTEM FOR PRESENTING AND RENDERING LOGIC SPECIFICATIONS OF INTERACTIVE SYSTEMS
(Eurographics Association, 1990) Johnson, C.W.; Harrison, M.D.
Formal specifications provide the non-specialist with an extremely poor impression of what it would be like to interact with a computer system. Prototypes provide a far better impression of the ‘look and feel’ of possible implementations but lack the precision of more formal approaches. Unfortunately, specification and prototyping are typically treated as alternatives. If these two activities can be harnessed then the designer has a means of incorporating the user into systems design. Tools can ease the transition from specification to prototype by supporting the visualisation of a design in terms of graphical representations of the proposed system. This paper describes Prelog, a tool for Presenting and REndering LOGic specifications of interactive systems. Prelog supports the structured representation of interaction objects which describe virtual devices. Interaction objects support reasoning about prototypes because they provide a means of abstracting away from device dependent pragmatics which make renderings intractable.
Fast Rendering of Arbitrary Distributed Volume Densities
(Eurographics Association, 1990) Sakas, Georgios
In recent years a number of techniques have been developed for rendering volume effects (haze, fog, smoke, clouds, etc.). These techniques are either time consuming (ray-tracing, radiosity) or do not account for arbitrary density distributions. In this paper we briefly analyze the physics of illuminations of volumes and we propose several simplifications suitable. for computer graphics practice. In particular, we present a method for rendering arbitrary distributions by means of projective polygonal rendering and solid texturing techniques in approximately the time needed for a usual polygonal object. The proposed method provides good results in a fraction of the computing time required for approaches like ray-tracing or radiosity. Solid texturing is used to define the density distribution and a point-sampling Monte-Carlo method with user-adjustable accuracy to evaluate the illumination model along the path through the volume. Thus, a trade-off between computing time and picture quality exists. With this technique one can move through or around the volume and to place objects and/or light sources in the volume. By means of rendering methods like shadowing polyhedra, objects can cast shadows on the volume and/or the volume can shadow the ground.
Tightly-Coupled Multiprocessing for a Global Illumination Algorithm
(Eurographics Association, 1990) Drettakis, George; Fiume, Eugene; Fournier, Alain
A prevailing trend in computer graphics is the demand for increasingly realistic global illumination models and algorithms. Despite the fact that the computational power of uniprocessors is increasing, it is clear that much greater computational power is required to achieve satisfactory throughput. The obvious next step is to employ parallel processing. The advent of affordable, tightly-coupled multiprocessors makes such an approach widely available for the first time. We propose a tightly-coupled parallel decomposition of FIAT, a global illumination algorithm, based on space subdivision and power balancing, that we have recently developed. This algorithm is somewhat ambitious, and severely strains existing uniprocessor environments. We discuss techniques for reducing memory contention and maximising parallelism. We also present empirical data on the actual performance of our parallel solution. Since the model of parallel computation that we have employed is likely to persist for quite some time, our techniques are applicable to other algorithms based on space subdivision.
Cross Scanline Algorithm
(Eurographics Association, 1990) Tanaka, Toshimitsu; Talcahashi, Tokiichiro
This paper proposes a new hidden surface removal algorithm which is based on the scanline algorithm but scans in two directions, horizontally and vertically. Named the cross scanline algorithm, it can efficiently detect all polygons and calculate their exact projected areas in each pixel even if the polygons are much smaller than the pixel. Comparisons with the regular sub-scanlines algorithm show that high quality anti-aliased images can be generated.
EDEN - AN EDITOR ENVIRONMENT FOR OBJECT- ORIENTED GRAPHICS EDITING
(Eurographics Association, 1990) Fellner, Dieter W.; Kappe, F.
Systems allowing the creation and manipulation of graphical information (so-called Graphic Editors) have become essential in various fields of applications. At the same time the typical user of such a system has changed. Not computer experts, but designers, secretaries, technicians, teachers etc. are today's typical users of computer graphics, mostly on microcomputers. Obviously it would be desirable to have a common concept of graphics editing covering many applications. The purpose of this paper is a brief survey of the EDEN project started at the IIGb in 1987: the motivation for the project, the major steps, results, current status and future work is presented here. EDEN (short for EDitor ENvironnient) is a generic concept for object-oriented graphics editing, providing device independence at the workstation and graphics output level as well as an application independent file-format for the storage and exchange between different graphics applications.
TRIES: DATA STRUCTURES BASED ON BINARY REPRESENTATION FOR RAY TRACING
(Eurographics Association, 1990) Thirion, Jean-Philippe
Tries are data structures used for multidimensional searching. We introduce an original method to build Tries for a set of convex polyhedra, weshow how Tries can be used for Ray tracing and we compare them with other data structures. Their advantages are mainly compactness of memory representation and fast building of the structure due to simple binary operations. Tries also accelerate the Ray tracing process compared to other octree-like structures. Furthermore, they are easy to implement because they are a unified approach to multidimensional problems. Finally we show experimental results to compare them with other data structures used for image synthesis.
Factoring a Homogeneous Transformation for a more Efficient Graphics Pipeline
(Eurographics Association, 1990) Abi-Ezzi, Salim S.; Wozny, Michael J.
We identify an intermediate coordinate system situated between world coordinates and display coordinates, which exhibits unique features for lighting calculations and for clipping in homogeneous coordinates. Our key contribution is an algorithm for extracting such a coordinate system from a homogeneous viewing transformation that relates WC to DC. The algorithm is based on factoring the transformation into a product of a Euclidean factor and a sparse (computationally cheap) but non- Euclidean factor. A particularly strong application of the proposed technique is the graphical processing of curved surface primitives, such as what is needed in the PHIGS PLUS viewing pipeline. Furthermore, in PHIGS PLUS the graphical data is retained by the graphics system, therefore, it is possible to perform the factoring of the viewing transformation at creation time, and to take advantage of this factored form at traversal time.
AN INTERPOLATION METHOD FOR STOCHASTIC MODELS
(Eurographics Association, 1990) Ramstein, G.
This paper presents a method using stochastic models for the simulation and interpolation of natural phenomena. These models are based on the general concept of random functions with stationary increments, to which the fbm belongs. The consideration of this family of stochastic processes, instead of just considering the fractal one, leads to greater diversity and realism. Another way to enhance realism is to combine analysis and interpolation. We suggest calculating the stochastic parameters from the analysis of existing natural surfaces and to use them as input data for the interpolation algorithm. We propose an interpolation algorithm which respects the stochastic behavior of this class of processes. This method provides a better understanding of the interpolation mechanisms. One can thus study the influence of the stochastic parameters and the data points localization on the interpolated valued. A final advantage of this algorithm is to interpolate surfaces defined by irregular data points. This type of representation is actually often encountered in cartography (contour lines, spot elevations, ...). This possibility is also very interesting for image synthesis applications, since it allows specifying with ease the rough shape of a given image.
INTERPOLATING CURVE NETWORKS WITH NEW BLENDING PATCHES
(Eurographics Association, 1990) Saitoh, Tsuyoshi; Hosaka, Mamoru
This paper describes methods of c o n s t r u c t i n g s u r f a c e patches which s a t i s f y independently given boundary conditions on a l l i t s four or t h r e e s i d e s . A patch c o n s i s t s of two p a r t s : one i s a patch s a t i s f y i n g a t l e a s t p o s i t i o n a l condition of the boundary curves, and the other gives n u l l position vectors and independent i t s f i r s t and second d e r i v a t i v e vectors on t h e i r boundaries. The l a t t e r i s used for compensating d e r i v a t i v e vectors t o s a t i s f y given boundary conditions. A network o f curves whose meshes are four or t h r e e s i d e s can be i n t e r p o l a t e d smoothly with patches of t h i s type.
A Stochastic Functional Approach for Terrain Modeling
(Eurographics Association, 1990) Dong, Jun-Cai; Peng, Qun-Sheng; Liang, You-Dong
A new functional modeling approach - -functional modeling, is presented to depict various classes of natural terrain. While this approach possesses the functions of several previous methods, it does not suffer the drawbacks of creases or periodity. By choosing the control parameters properly, our approach can easily generate different terrains related to various smoothness, such as cliffs,fractal mountains and smooth terrains. It can also simulate the natural weathering processes as from the cliff to the fractal mountain and to the smooth terrain not only in the appearance but also in quantity. And it is capable of modeling the terrain whose "rock bed” and "rock quilt" are associated with different smoothness.
AN INTERACTIVE DEBUGGER FOR PHIGS
(Eurographics Association, 1990) Howard, T.L.J.; Hewitt, W.T.; Larkin, S.
The Programmer’s Hierarchical Interactive Graphics System (PHIGS) is an International Standard for integrating application modelling and interactive computer graphics. With PHIGS, application models are constructed from hierarchical data structures called structure networks, which may be edited interactively. While structure networks are in principle straightforward to create, organising and managing them correctly is in practice a much more difficult proposition. One of the main difficulties arises from the atomic nature of the traversal process by which structure networks are interpreted for display. This paper draws an analogy between structure network traversal and programming language execution, and presents the PHIGS Debugger, a development tool for PHIGS applications. The PHIGS Debugger supports interactive incremental traversal of structure networks and debugging of the PHIGS Centralised Structure Store, and is a component of the PHIGS Toolkit, an emerging set of portable integrated tools for PHIGS environments. 1
AN OBJECT ORIENTED APPROACH TO ENSURE PORTABILITY OF CAD STANDARD PARTS LIBRARIES
(Eurographics Association, 1990) Pierra, Guy
The integration, in CAD systems, of libraries of standard parts is often considered to be one of the key factors for increasing productivity of Computer Aided Design [1] [2] [3]. These libraries must be able to integrate homogeneously both the standard components external to the firm (standardized items and suppliers' standards) and internal firm-specific standards.
COLOR SHADING IN 2D SYNTHESIS
(Eurographics Association, 1990) Bourdin, J.J.; Braquelaire, J.P.
In interactive 2D synthesis applications, features for filling regions are generally elementary (uniform colouring, filling with a regular pattern.. .). Interactive design of 2D colour shadings raises two major problems: the difficulty of specifying a shading precisely, and the rapidity of related filling algorithms. In this paper, we propose a model to specify 2D colour shading of a region by decomposing it into two components: a support describing the “shape” of the shading, and a colouring function defined on this shape. We then present an incremental algorithm for support generation.

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