Editing Ray casting (section)

=== Line Drawings ===

[[File:Example line drawings.jpg|thumb|Example line drawings made by casting rays. Two are standard plan views. One shows hidden edges as dashed lines.]]To draw the visible edges of a solid, generate one ray per pixel moving top-down, left-right in the screen. Evaluate each ray in order to identify the visible surface S[1], the first surface pointer in the sorted list of ray-surface intersections. If the visible surface at pixel location (X, Y) is different than the visible surface at pixel (X−1, Y), then display a vertical line one pixel long centered at (X−½, Y). Similarly, if the visible surface at (X, Y) is different than the visible surface at pixel (X, Y−1), then display a horizontal line one pixel long centered at (X, Y−½). The resulting drawing will consist of horizontal and vertical edges only, looking jagged in coarse resolutions.

Roth’s ray casting system generated the images of solid objects on the right. Box enclosures, dynamic bounding, and coherence were used for optimization. For each picture, the screen was sampled with a density of about 100×100 (e.g., 10,000) rays and new edges were located via binary searches. Then all edges were followed by casting additional rays at one pixel increments on the two sides of the edges. Each picture was drawn on a Tektronix tube at 780×780 resolution.