EG1989 Proceedings (Technical Papers)

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2.5 Dimensional Graphics Systems
(Eurographics Association, 1989) Herman, Ivan
The outline of an extension of traditional 2D graphics systems is given. This extension is aimed at supporting a three dimensional application program, without incorporating full viewing into the general graphics system itself. The resulting system might be very advantageous for large application programs which have their own three dimensional facilities.
Accelerated Radiosity Method for Complex Environments
(Eurographics Association, 1989) Xu, Hau; Peng, Qun-Sheng; Liang, You-Dong
As form-factor calculation costs about 90% of the computing time when applying radiosity approach for realistic image synthesis, it is of great significance to reduce the required computation, An accelerated radiosity algorithm for general complex environments, based on environment localization and the directional form-factor concept, is presented in this paper. First we subdivide the object space into many regions. Objects contained in each region are adjacent to each other and pose more illumination effects to their neighbours. Then form-factors are calculated in each local environment,. The radiant light energy transfer between different regions is evaluated at their common boundaries. Directional form-factors are introduced to simulate the interaction of light between local environments and between non-diffuse surfaces. Comparison is made to existing algorithms. Statistic results and theoretical analysis show that the new algorithm is much faster than previous ones. The technique is especially fit for interactive design and animation sequence since modification to the shape or location of objects usually happens in local environments.
Adding Parallelism in Object Space to the Rendering Pipeline
(Eurographics Association, 1989) Chapman, Paul A.; Lewis, Eric
This paper analyses the problem of adding parallelism to the rendering pipeline and discusses the reasons for advocating an object-space partition. Consideration of the methods of work distribution and the rendering techniques which are desired, leads to the proposition of two algorithms for performing the partition. An architecture for their implementation is considered and evaluated.
Algorithms for 2D Line Clipping
(Eurographics Association, 1989) Skala, Vaclav
New algorithms for 2D line clipping against convex, non-convex windows and windows that consist of linear edges and arcs are being presented. Algorithms were derived from the Cohen-Sutherland 's and Liang-Barsky s algorithms. The general algorithm with linear edges and arcs can be used especially for engineering drafting systems. Algorithms are easy to modify in order to deal with holes too. The presented algorithms have been verified in TURBO-PASCAL. Because of the unifying approach to the clipping problem solution all algorithms are simple, easy to understand and implement.
An Analysis of Modeling Clip
(Eurographics Association, 1989) O Bara, Robert M.; Abi-Ezzi, Salim
Modeling clip gives an application the ability to remove sections of an object in order to view internal detail. The clipping volume defied by modeling clip can be concave and disjoint, and is composed of a set of volumes that are specified in modeling coordinates. The modeling clip functionality has been included in the PHIGS specification [4], Some interesting peculiarities arise from the fact that most graphics pipelines (such as PHIGS) are algebraically based and that modeling clip regions are specified in modeling coordinates. One such peculiarity occurs when the transformation relating the coordinate system of the clip region to world coordinates is singular. A study on the algorithmic and architectural issues of implementing modeling clip is presented. The resulting algorithm to implement the modeling clip mechanism represents the clip volume as a pipeline of filters with each filter representing one of the sub-volumes. The method handles all of the sixteen possible set combinations between two regions in space. The effects of transformations on modeling clip have been examined, and has resulted in identifying when modeling clip can be efficiently performed in device coordinates as well as the cases when it can not. When handling singular modeling transformations, it is shown that it i
Anti-Aliasing by Successive Steps with a Z-Buffer
(Eurographics Association, 1989) Ghazanfarpour, D.; Peroche, B.
We present a method allowing to solve the three problems arising when a scene is displayed with the z-buffer algorithm. The proposed algorithm only requires one extra memory bit per pixel and delivers good quality images. It is fast because, in particular, the most expensive calculations such as antialiasing or texture mapping are made only for visible pixels of the scene.
Blending Rational B-Spline Surfaces
(Eurographics Association, 1989) Bardis, L.; Patrikalakis, N.M.
A method for blendin non uniform rational B-spline surface patches, either open or periodic, is developed. he blending surface is expressed in terms of an integral, bicubic B-spline patch. The blend ensures position and normal vector continuity along linkage curves to within a specified accuracy. The linkage curves are either user-defined or are obtained by offsetting the intersection of the two patches using geodesics on each patch. An example illustrates the applicability of our method.
Colour Section
(Eurographics Association, 1989) -
Components, Frameworks and GKS Input
(Eurographics Association, 1989) Duce, D. A.; Ten Hagen, P.J.W.; Van Liere, R.
This paper was inspired by the Components/ Frameworks approach to a Reference Model for computer graphics, currently under discussion in the ISO computer graphics subject committee. The paper shows how a formal description of the GKS input model may be given in Hoare’s CSP notation and explores some extensions in which some of the components in the GKS model are replaced by more interesting ones. The paper thus demonstrates some of the power and flexibility inherent in the Component/ Frameworks idea. The use of a formal notation led to a deepening of the authors’ understanding of the input model and suggested some different ways of looking at the input model.
Deformation of Solids with Trivariate B-Splines
(Eurographics Association, 1989) Griessmair, Josef; Purgathofer, Werner
Solid geometric models can be deformed to free-form solids by the use of trivariate B-splines. This paper describes the problems of implementing such transformations for shaded rendering. The surfaces are subdivided into triangles adaptively so that the error in image space is limited. This adaptive triangulation ensures a smooth appearance of the resulting pictures.
Delauney Triangulations and the Radiosity Approach
(Eurographics Association, 1989) Schuierer, Sven
The radiosity approach requires the subdivision of complex surfaces into simple components called patches. Since we assume to have constant intensity over a patch, the generation of regular patches is a desirable property of the subdivision algorithm. We show that constrained Delaunay triangulations produce patches that are as close to equilateral triangles as possible and thus are well suited for the partitioning of surfaces into patches. Since a number of optimal algorithms to generate constrained Delaunay triangulations have been published, the implementation presented here made use of the earlier work. The implementation consists of a rather simple modeling tool called POLY, a fast triangulation algorithm for arbitrary polygons and the form factor computation combined with a z-buffer output module.
Forest of Quadtrees: An Object Representation for 3D Graphics
(Eurographics Association, 1989) Kaufman, Arie; Bandopadhay, Amit
A forest of quadtrees is proposed as an alternative data structure for representing and manipulating 3D and 2.5D graphics. A data representation of a forest offers space savings over common quadtrees by concentrating the vital information and discarding unused pointers. Several properties of the forest of quadtrees and the basic operations for display and elementary transformations like rotation, reflection, enlargement, reduction, and translation are investigated. Specifically, the temporary memory requirements and duplication time of the algorithms are analyzed.
GEO++ - A System for Both Modelling and Display
(Eurographics Association, 1989) Wisskirchen, Peter
We present a new concept for a graphics system which we call GEO++ . Apart from the manipulation of groups (structures in PHIGS-terminology), GEO++ permits a direct access to the tree structure required for display. With this concept we believe to have achieved a synthesis between the requirements of modelling in the sense of manipulation of building patterns and of display in the sense of editing individual objects (parts) on the screen.
GKS, Structures and Formal Specification
(Eurographics Association, 1989) Duce, D. A.
There are now three International Standards for application program interfaces for computer graphics programming, GKS, GKS-3D and PHIGS. In this paper a simplified model GKS-like system is described and a 2D PHIGS-like system is then described in terms of this and a centralized structure store. Formal specifications of the systems are given illustrating how the specification of a system can be built up from a hierarchy of simple components. The purpose of the paper is to illustrate one approach to the description of a compatible family of graphics standards and the use of formal specification techniques in this process.
Graph Grammars, A New Paradigm for Implementing Visual Languages
(Eurographics Association, 1989) Goettler, Herbert
This paper is a report on an ongoing work which started in 1981 and is aiming at a general method which would help to considerably reduce the time necessary to develop a syntax-directed editor for any given diagram technique. The main idea behind the approach is to represent diagrams by (formal) graphs whose nodes are enriched with attributes. Then, any manipulation of a diagram (typically the insertion of an arrow, a box, text, coloring, etc.) can be expressed in terms of the manipulation of its underlying attributed representation graph. The formal description of the manipulation is done by programmed attributed graph grammars.
Hierarchical Texture Synthesis on 3-D Surfaces
(Eurographics Association, 1989) Bennis, Chakib; Gagalowicz, Andre
This paper presents a new method for synthesizing hierarchical textures on 3-D surfaces. This method utilizes both a mapping technique for rendering the macroscopic structure on the surface and a generalization of the direct 3-D microscopic synthesis algorithms (presented in earlier publications) for generating a homogeneous texture inside each pattern. To produce the macroscopic structure on the 3-D shape a new mapping technique is proposed. With this technique patterns distortion is minimized locally. Finally a solution to the aliasing problem adapted to our mapping is given.
Highlight Shading: Lighting and Shading in a PHIGS+/PEX-Environment
(Eurographics Association, 1989) Poepsel, J.; Hornung, C.
Todays graphics standard for the rendering of scenes with illumination and reflection is defined by PHIGS+ . PEX is a proposal to integrate that functionality into the window environment of X. This paper first describes the lighting and shading models of PHIGS+/- PEX . Then a comparison of the different shading methods follows. At last, a new shading method, the Highlight Shading, is developed. The Highlight Shading combines both speed and image quality and therefore is an attractive alternative to existing shading algorithms.
The Macro-Regions: An Efficient Space Subdivision Structure for Ray Tracing
(Eurographics Association, 1989) Devillers, Olivier
Ray tracing is the usual image synthesis technique which allows rendering of specular effects. The use of space subdivision for ray tracing optimization is studied. A new method of subdivision is proposed : the macro-regions. This structure allows a different treatement of the regions with a low density of information, and the regions with a high density of information. A theoretical and practical study of space subdivision methods -grid, octree- and the macro-regions structure is presented.
Message-Based Object-Oriented Interaction Modeling
(Eurographics Association, 1989) Breen, David E.; Kühn, Volker
This paper describes a message-based object-oriented tool for exploring mathematically-based interactions which produce complex motions for computer animation. The tool has been implemented as an object in the object-oriented computer animation system The Clockworks. It supports the definition of complex interactions between geometric objects through the specification of messages to the interacting objects. Our approach is general, flexible and powerful. The tool itself is not hardcoded to a particular application. It simply sends the messages specified by the user. Messages are specified as strings which may be stored, modified and interpreted. Since the tool is part of The Clockworks it may utilize many of the powerful features of the system, including data structuring, mathematical, geometric modeling, and rendering objects. The tool has been used to explore a general spring and mass model, and the response of objects in a vector field.
MICRO-UIDT: A User Interface Development Tool
(Eurographics Association, 1989) Mao, Qijing
A user interlace development tool called Micro-UIDT is described. Micro-UIDT provides an interactive design environment fur the user interface designers. The designing language for defining user interfaces are visual and nonprocedural. State transition diagrams are used as the notation for specifying man-machine dialogue control. Some extensions are added into the notation, so that the user interfaces with semantic feedback can be defined. The approach of specifying the presentation of application data is bottom-up and direct operation. The designing language for this has two major description facilities, one for describing graphics and another for describing the relationships between the graphics and the application variables. A concept of graphic object is used in the language, which can make the design result be abstracted and reused. The user interfaces developed with Micro-UIDT are small in size and fast in speed.

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