Browse Prior Art Database

Method of Correlating on Areas in an Interactive Display System

IP.com Disclosure Number: IPCOM000062050D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Normington, G: AUTHOR

Abstract

The method of correlating straight lines in an interactive display system described in European Patent Application EP-A-0163872, published December 11, 1985, is extended to provide for correlation on areas defined by boundary lines. By using the method of EP-A-0163872, it can be determined whether any of the boundary lines intersects a selected rectangular window. If so, then the defined area must intersect the window. If not, however, the area may be complex and intersect the window even though the boundary lines do not. Thus, boundary lines 2 forming a square (Fig. 1) may surround the window 4 so that the area intersects, or an annular area between two sets of square boundary lines 6 and 8 (Fig. 2) may not.

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Method of Correlating on Areas in an Interactive Display System

The method of correlating straight lines in an interactive display system described in European Patent Application EP-A-0163872, published December 11, 1985, is extended to provide for correlation on areas defined by boundary lines. By using the method of EP-A-0163872, it can be determined whether any of the boundary lines intersects a selected rectangular window. If so, then the defined area must intersect the window. If not, however, the area may be complex and intersect the window even though the boundary lines do not. Thus, boundary lines 2 forming a square (Fig. 1) may surround the window 4 so that the area intersects, or an annular area between two sets of square boundary lines 6 and 8 (Fig. 2) may not. According to the present method, each line that is found not to intersect by the method of EP-A-0163872 is subjected to the present method to determine whether it crosses a line 10 from the window 4 to infinity. A count is kept of such crossings, and if this is even, there is no intersection, but if odd, then there is intersection. Conveniently, the line 10 starts from the top left- hand corner 12 of the rectangular window 4. After step 4 of the previous method, which indicates that a line has not intersected the window, Step A (Fig. 3) of the present method is entered. In this it is determined whether the outcodes of the endpoints of the line differ in both bit 3 and bit 4. If so, e.g., line 2A (Fig. 1), then Step B follows. If not, then Step...