Abstract
This paper describes an algorithm for displaying shaded images of Constructive Solid Geometry (CSG) objects. The algorithm was originally proposed by Woodwark 1 for planar surfaces and has been substantially extended in a Pascal implementation, WINSOM, by Peter Quarendon at the IBM UK Scientific Centre. 2 It uses an Octree subdivision technique to produce shaded images quickly and directly from CSG trees of quadric surfaces without the need for faceting or boundary evaluation. Boundary evaluation is an O(N 4) algorithm where N is the number of primitive surfaces, and is a major bottleneck in the display of highly complex CSG solids. The runtime of the algorithm is dependent on the screen resolution and is approximately linear in the number of primitive objects to be displayed. This has made it practicable to display CSG objects containing tens of thousands of primitives which would take days to display by boundary evaluation.
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