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Item A Statistical Comparison of Two Hidden Surface Techniques: the Scan-line and Z-buffer Algorithms(Blackwell Science Ltd and the Eurographics Association, 1992) Slater, Mel; Drake, Kieron; Davison, Allan; Kordakis, Emmanouell and Billyard, Adam and Miranda, EliotThis paper compares two image space hidden surface removal algorithms for polygonal scenes. These are the z-buffer and scan-line algorithms. There is first an overview of each algorithm, followed by a simulation experiment, designed to compare the number of polygons per second which can be rendered by each algorithm. The simulation varies the number of polygons in the scene, and the size and distribution of polygons over the display. The results suggest that the z-buffer is preferred for a large enough number of polygons, however, smaller polygons and uniform distribution of polygons favour the scan-line approach. The analysis does not take into account the complexity of the shading rule, which is likely also to favour the scan-line method.Item A Multiprocessor Implementation of Radiosity(Blackwell Science Ltd and the Eurographics Association, 1993) Ng, Adelene; Slater, MelThis paper describes a multi-processor implementation of form factor computation in the radiosity method. Form factors are computed using the ray casting method and the algorithm is enhanced with Binary Space Partition (BSP) Trees and bounding boxes. Experimental results are presented together with a discussion of load balance efficiency.Item Liberation from Rectangles: A Tiling Method for Dynamic Modification of Objects on Raster Displays(Eurographics Association, 1988) Slater, Mel; Davison, Allan; Smith, MarkWhen graphics objects (also called segments) are used on raster display hardware, problems arise because of the mismatch between the high level requirements of object manipulation, and the low level representation from which the image is refreshed. This paper describes a tiling algorithm which provides a solution to the problems of damage repair and hit detection. In particular methods for handling object priority are discussed and experimental results showing the performance of the algorithm for a number of cases are presented.Item A Top Down Method for Interactive Drawing(Blackwell Publishing Ltd and the Eurographics Association, 1988) Slater, MelTraditional interactive drawing programs adopt a bottom-up approach, allowing the user to construct a picture by the use of discrete tools, for example, lines, circles, rectangles, and so on. This paper presents a different approach, which allows users to construct graphical objects by stretching and cutting existing objects. The representation is simply implemented, based on a ring of cubic Bezier curves, and use of the de Casteljau algorithm.Item Liberation from Flatland: 3D Interaction Based on the Desktop Bat(Eurographics Association, 1991) Slater, Mel; Davison, AllanA novel device for 3D interaction is introduced, the Desktop Bat. This device is an evolutionary development of a mouse. It is like a mouse in that it is used on a desktop, but provides 5 degrees of freedom since in conjunction with translations it can be used to effect rotations about any combination of the principal axes. We discuss the requirements for 3D interaction which led to the design of the Desktop Bat, and the interaction models and software which allow it to be used as a 6 degrees of freedom input device.Item Graphics Object Management in The X Window System(Blackwell Publishing Ltd and the Eurographics Association, 1990) Davison, Allan; Slater, Mel; Smith, MarkThis paper describes a library for the creation and manipulation of geometrically defined graphical objects in The X Window System Objects are arranged in a 2.5D space, and can be transformed, made invisible or visible, or have their priority changed. Transformation of objects occurs immediately and with full damage repair, thus providing an essential requirement for the support of interactive graphics. The paper reports on an experimental implementation of the library and also discusses the implications of graphical objects in the X environment.Item Distributed Frame Buffer for Rapid Dynamic Changes to 3D Scenes(The Eurographics Association, 1992) Coppen, Derek; Slater, Mel; Davison, Allan; Hawes, David; P F ListerThis paper describes a distributed frame buffer architecture, based on the Tiling Algorithm for dynamic modification, and designed to achieve fast display updates inresponse to dynamic transformations of graphical objects. We report on the overall architecture and some detailed design issues.