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Show algorithm for drawing parametrically defined surfaces CHAPTER 3 SCAN LINE BASED ALGORITHMS The Moving Finger writes; and, having writ, Moves on: nor all thy Piety or Wit, Shall lure it back to cancel half a Line, Nor all thv Tears wash out a Word of it. The·Rubaiyat of Omar Khayyam Algorithms which generate picture elements in a scan line order (left to right, top to bottom) have two main advantages. The intensity of each picture element is computed completely before going on to the next, using all of the information necessary about the parts of the scene visible in that picture element. This makes anti-aliasing computations relatively easy to perform. In addition, scan line algorithms are more suited for hardware implementation as they generate the intensities in the same order as a television monitor scans them out on the screen. The presentee in this thesis is a generalization of many of the more widely known polygonal (planar) surface algorithms and second order (quadric) algorithms. To build the proper foundation for the parametric surface algorithm it is necessary to first review previous work. In so doing, we will pay closest attention primarily to the geometric calculations involved, that is, the determination of what parts of what surfaces fall within a particular picture |
