Issue 4

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https://diglib.eg.org/handle/10.2312/57

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    The Determination of Form-Factors by Lookup Table
    (Blackwell Science Ltd and the Eurographics Association, 1993) Sun, Jizhou; Zou, L.Q.; Grimsdale, R.L.
    Current methods for computer image synthesis using the radiosity algorithm rely heavily on the calculation of geometrical properties, known as form-factors, which quantify the energy exchange between pairs of surfaces in the environment. In this paper, a new method for form-factor calculation is presented, in which form-factors from a differential area to a finite area with various geometric orientations and dimensions can be determined by the summation of three weighted directional form-factors. The three directional form-factors are mutually independent and can be pre-calculated and stored in a lookup table accessed by two indices. Thus, the determination of the generally used complex form-factor integral is greatly simplified and mainly replaced by accessing a pre-established lookup table. Quantitative comparisons of Wallace s ray casting method and the method presented indicate that the new method can provide more accurate form-factors, which implies that the number of sample points necessary on each source patch is comparatively reduced and the process of form-factor calculation can be accelerated.
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    A Library for Developing PHIGS Programming Tools in a PEX Environment
    (Blackwell Science Ltd and the Eurographics Association, 1993) Wainer, Michael; Tan, Ting
    The merger of three-dimensional graphics with the X Window System has recently been standardized by adapting PHIGS, the Programmer s Hierarchical Interactive Graphics System, to the X Window System with PEX, the PHIGS Extension to X. The standard programming library for PEX has been defined to be identical to PHIGS PLUS allowing PHIGS programs to port directly to the X environment. X uses a client server model to run applications as client processes which communicate with a server to perform graphical display and input. For improved performance, the PEX extension defines new server resources to reduce network traffic and to take advantage of graphics hardware existing on high-end servers. A side effect of this distributed model of computation is a distribution of PHIGS structures leading to a relaxation of the exclusive access which a PHIGS application usually maintains over its Central Structure Store.We exploit the distributed nature of a PEX/PHIGS client s Central Structure Store to provide access to it for other applications besides the originating PEX/PHIGS client. We refer to these other applications as tools since one of our primary goals is to create development tools for PHIGS programmers. Rather than concentrate on particular debugging tools, we focus upon easing the process of actually developing tools. Our goal is to supply a collection of routines which can be used by PHIGS programmers to create custom tools or other programs which require access to the graphics data of remote PHIGS processes.Our Tool Development Library provides the PHIGS programmer a small number of management routines which orchestrate the connection and mapping to the data of one or more remote PHIGS applications. Manipulation of remote PHIGS structures is accomplished just as easily as local operations and is performed using standard PHIGS calls. The remote application being accessed requires no changes to its source code. Obvious uses for the Tool Development Library are in the construction of PHIGS tools such as structure browsers, editors and debugging aids. Less obvious is the potential for developing collections of cooperating graphics applications which share graphics data.
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    Ray Tracing an Octree: Numerical Evaluation of the First Intersection
    (Blackwell Science Ltd and the Eurographics Association, 1993) Gargantini, I.; Atkinson, H. H.
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    Spanning a C1-Surface over a Given Wireframe
    (Blackwell Science Ltd and the Eurographics Association, 1993) Tokumasu, Shinji; Harashima, Ichirou; Nakajima, Norihiro
    A problem of spanning a surface of C1 continuity (C1-surface) over a given wireframe is introduced. By exploiting the concept of a super surface patch introduced in an earlier paper, we proved the existence of an approximate, yet practical solution of the problem. That is, we presented a method or a procedure, by which to span a C1-surface over the wireframe. This technique is intended to be utilized as a flexible surface generation method for the 3D shape design in the industrial world.