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Item Free-Form Surfaces Modeling by Evolution Simulation(Eurographics Association, 1988) Lienhardt, PascalWe present in this paper a procedural method for modeling free-form, planar surfaces subdivisions, which allows simulating evolutions of such subdivisions. This method is founded on the common principles deduced from corpuscular phenomena modeling method (particle systems), and method for vegetal trees modeling by simulation of evolution. These principles are : - use of a discrete model, which is a set of basic elements, from which time discretization is deduced, -proper activity of basic elements; these methods consists in simulating the behaviour of these elements; - characterization of modelled object evolution, which is achieved by "functions" associated to basic elements; - priority of topology over geometry. A surface is defined as a set of surface elements, supported by a rooted, planar tree. A surface is initially reduced to a point. Surface evolution characterization and control are exclusively exerted through this tree. This method is applied to image synthesis and animation of natural shapes, especially vegetal shapes.Item Computer Generation of Penrose Tilings(Blackwell Publishing Ltd and the Eurographics Association, 1988) Rangel-Mondragon, J.; Abas, S.J.Item Architectures for Mass Market 3D Displays(Eurographics Association, 1988) Winser, Paul; Bonnet, Thierry; Dumont, Dominique; Mathieu, YvesWe discuss the specific architecture requirements of real time 3D display systems intended for low cost mass market products of the near future. Vertex transformation and polygon rendering are two processing aspects where hardware acceleration must be used to achieve the performance target. The use of one or more DSP chips as vertex processors is discussed, and two efficient z-buffer implementations described. Antialiasing and texture mapping greatly improve the visual impression at some processing cost.Item A Proposal for a Distributed Model of GKS Based on Prolog(Blackwell Publishing Ltd and the Eurographics Association, 1988) Milanese, V.The Graphical Kernel System GKS is so well established as a standard for graphics programming that quite a number of models for multiprocessor and distributed environments have already been suggested. It is therefore necessary to consider new languages and methodologies capable of supporting its distributed implementation. In this context, clausal logic languages provide suitable means for describing the system in a declarative form and, moreover, ensure the applicability of meta-programming techniques for specifying the semantics of implementation. The Prolog language, extended with communication and modularization structures required by the distributed programming, is thus here considered as a feasible means for establishing a model of GKS organized in functional modules which could be supported by different processors. For such a model a two-level implementation scheme is outlined and a reconfiguration and personalization methodology is suggested.Item An Evaluation of CSG Trees Based on Polyhedral Solids(Eurographics Association, 1988) Badouel, Didier; Hegron, GerardSet operation on polyhedra is an important component of Geometric Modeling System (GMS) when a Constructive Solid Geometry (CSG) representation with polyhedral solid primitives is used. Output data will be the unique resulting polyhedron which provides an efficient data structure for displaying objects. With no use of spatial coherency, computational complexity of a set operation is quadratic. The new evaluation scheme called Boolean Octree limits set operation evaluation in a ‘minimal space of calculation’ where primitive boundaries intersect each other and where resulting evaluation participates in the construction of the final resulting object. Boolean Octree computes set operations in a local level providing a linear complexity for geometric calculations. During space subdivision, Boolean Octree has a global view on local CSG tree (projection of the CSG tree in local space) taking into account simplifications of the boolean expression. Set evaluation is done in the local volumes containing only two operands the configurations of which are ‘simple’, that is to say for a local description of an object there is only one vertex with any face number, one edge, or one face.Item Point-driven Generation of Images from a Hierarchical Data Structure(The Eurographics Association, 1988) Jong, Dirk de; Siobbe, Paul van; Splunter, Marinus van; A. A. M.KuijkIn this paper, a system IS described which renders an image from a hierarchical data structure in a point-driven way. The data structure allows dynamic color mapping and arbitrary affine transformat·ons of objects with respect to their parent coordinate system. The point driven method allows for easy VLSI implementation, efficient use oj memory and exploitation of parallelism.Item A Note on Random Thresholding for Colour Synthesis(Blackwell Publishing Ltd and the Eurographics Association, 1988) Lastra, G.L.; Rudinger, E.N.A simple algorithm that improves colour shaded images is presented. The algorithm does not trade spatial resolution for intensity resolution. The basic technique, based on random thresholding modulated by a pseudo-random number generator of uniform distribution, is introduced to render halftone images on bi-level displays. A generalization of the technique is done for displays with multiple bi-per-colour components. An obvious advantage of the algorithm presented over other reported methods is its simplicity. Pictures are included to show results of the algorithm.Item G1 Smoothing Solid Objects by Bicubic Bezier Patches(Eurographics Association, 1988) Liang, Youdong; Ye, Xiuzi; Fang, ShiaofenA general and unified method is presented for generating a wide range of 3D objects by smoothing the vertices and edges of a given polyhedron with arbitrary topology using bicubic Bezier patches. The common solution to the compatibility equations of geometric continuity between two Bezier patches is obtained and employed as the foundation of this new method such that this new solid and surface model is reliable and compatible with the solid modeling and surface modeling system in the most common use. The new method has been embeded in an algorithm supported by our newly developed solid modeling system MESSAGE. The performance and implementation of this new algorithm show that it is efficient, flexible and easy to manipulate.Item Combining Z-buffer Engines for Higher-Speed Rendering(The Eurographics Association, 1988) Molnar, Steven; A. A. M.KuijkDescribed IS a hardware architecture for combining the outputs of a number of z-buffer rendering engines to achieve higher performance than is possible with a single renderer. It allows a combination of renderers to achieve the same pllce!performance ratio as the individual renderers that compose it. and can be extended to create systems with arbitrarily high periormance.The desCribed architecture is based on a fusion of scan-line rendering and the conventional z-buffer algorithm. The frame buffers of several z-buffer engines are modified to scan out z-values as well as color values. Multiplexing devices combine the z/color streams from each pair of frame-buffers. These z/color streams are then combined by further multiplexers, creating a binary tree that funnels the z/color information from the many conventional frame buffers Into a single z/color stream. The color stream is then used to dnve a standard display device.The proposed architecture allows rendering rates of millions and even tens of millions of polygons per second. The basic architecture can be extended with additional hardware to perform antialiasing and texture-mapping.Item A Procedural System for the Definition and Storage of Technical Drawings in Parametric Form(Eurographics Association, 1988) Cugini, U.; Folini, F.; Vicini, I.The construction of a truly USER-FRIENDLY CAD system requires the acquisition and management of a tremendous amount of information which cannot be. and must not be. directly requested from the user, but which has to be obtained by intelligently interpreting the sequence of operations performed by him. The system described here is out forward as a USERFRIENDLY tool for the definition. storage and modification of technical drawings in parametric form. The system that has been implemented (GIPS Graphic Interactive Parametric System) assists the user during the steps of definition and modification. taking advantage of the abiIity to interpret the procedure the user follows in describing the object he wants to design.