Volume 08 (1989)
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Item 2-D Macroscopic Texture Synthesis(Blackwell Publishing Ltd and the Eurographics Association, 1989) Bennis, Chakib; Gagalowicz, AndreWe present a new macroscopic texture synthesis method based upon a hierarchical macroscopic texture model. Our model allows the composition of various patterns which can be themselves distorted spatially. Such a method is able to simulate a vast class of realistic macro-textures.Item 2.5 Dimensional Graphics Systems(Eurographics Association, 1989) Herman, IvanThe 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.Item 8th EUROGRAPHICS UK Conference(Blackwell Publishing Ltd and the Eurographics Association, 1989) Willis, P.J.Item Accelerated Radiosity Method for Complex Environments(Eurographics Association, 1989) Xu, Hau; Peng, Qun-Sheng; Liang, You-DongAs 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.Item Adding Parallelism in Object Space to the Rendering Pipeline(Eurographics Association, 1989) Chapman, Paul A.; Lewis, EricThis 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.Item Algorithm for Clpping Arbitrary Polygons(Blackwell Publishing Ltd and the Eurographics Association, 1989) Andreev, Rumen D.Item Algorithms for 2D Line Clipping(Eurographics Association, 1989) Skala, VaclavNew 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.Item An Analysis of Modeling Clip(Eurographics Association, 1989) O Bara, Robert M.; Abi-Ezzi, SalimModeling 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 iItem An Annotated PHIGS Bibliography(Blackwell Publishing Ltd and the Eurographics Association, 1989) Howard, T.L.J.Item Anti-aliased Ray Tracing with Covers(Blackwell Publishing Ltd and the Eurographics Association, 1989) Thomas, D.; Netravali, Arun N.; Fox, D.S.A fast and effective object space method for antialiasing ray-traced pictures is introduced. Traditionally, anti-aliasing has been done using super-sampling. However, this is costly since it requires casting large numbers of rays to obtain sample densities above the displayed pixel density. It is also wasteful since much of the information in these samples is discarded when they are filtered to yield the anti-aliased pixels. We avoid these problems by performing the filtering in the object space using the geometry of ray-surface intersections rather than by casting extra rays. In addition, we only perform filtering at a pixel if edges are nearby. We detect these edges by observing the order in which the pixel s rays pass through cover surfaces constructed just inside and outside the surface of each object. Shadows, reflections and refractions can be anti-aliased using this method and a variety of object types can be handled including ellipsoids, polyhedra, and objects formed using set operations.Our anti-aliasing gives a high image quality that can only be approached by using super-sampling densities at least four times the display pixel density. Moreover, since the overhead of our method is small, it would take three to four times as long to render an anti-aliased image using super-sampling than it would with our method. Furthermore, covers allow sampling densities less than the displayed pixel density. When this is done, anti-aliased images can be rendered twice as fast as with no anti-aliasing and six to eight times as fast as when super-sampling is used for anti-aliasing.Item 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.Item 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.Item Book Reviews(Blackwell Publishing Ltd and the Eurographics Association, 1989)Book reviewed in this article:Title: Image Synthesis - Elementary Algorithms Author: Gerard Hegron Translation (by D. Beeson) of: Synthese d Image: Algorithmes ElementairesCurves and Surfaces in Computer Aided Geometric Design Author: F. YamaguchiItem Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1989)Item Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1989)Item Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1989)Item Call for Participation in the EUROGRAPHICS WORKING GROUP on COMPUTER GRAPHICS HARDWARE(Blackwell Publishing Ltd and the Eurographics Association, 1989)Item Call for Participation in the EUROGRAPHICS WORKING GROUP on INTELLIGENT CAD(Blackwell Publishing Ltd and the Eurographics Association, 1989)Item Call for Participation in the EUROGRAPHICS WORKING GROUP on RELATIONSHIPS BETWEEN IMAGE SYNTHESIS and ANALYSIS(Blackwell Publishing Ltd and the Eurographics Association, 1989)Item Call for Participation in the EUROGRAPHICS WORKING GROUP on VISUALIZATION IN SCIENTIFIC COMPUTING(Blackwell Publishing Ltd and the Eurographics Association, 1989)