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Non-Reentrant Polygon Clipping Method

IP.com Disclosure Number: IPCOM000035374D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Lindgren, T: AUTHOR

Abstract

A method is described which eliminates the need for maintaining a polyline structure while clipping in three-dimensional regions. By reducing all clipping to line clipping, which is non-reentrant in character, performance of the method may be greatly enhanced by employing a parallel process.

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Non-Reentrant Polygon Clipping Method

A method is described which eliminates the need for maintaining a polyline structure while clipping in three-dimensional regions. By reducing all clipping to line clipping, which is non-reentrant in character, performance of the method may be greatly enhanced by employing a parallel process.

The method employs the following steps: 1. All edges of the polygon are clipped, and the clipped vectors are drawn (see Fig. 1). Clipped points are recorded in working registers. 2. Line segments and endpoints resulting from the plane of the polygon intersecting the front and back faces of the clipping volume are determined. This may be performed by taking the cross product of the first pair of visible vectors and using an endpoint of either vector to generate a plane equation. The plane equation shows the edges which intersect the plane and provide the inter

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section points, or, registers may be used to hold extreme value front and back face intersection points and those pairs clipped against the top, bottom, left and right to determine plane face intersection. 3. It is determined whether the extreme points of the line are in or out of the polygon. 4. The appropriate portion boundary of the clipping volume is drawn by collecting consecutive pairs of points from the working registers beginning with either the first point found or the second point. Six lines must be examined because a plane may intersect a parallel piped in...