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line-intersection-demo.r

REBOL [ File: %line-intersection-demo.r Date: 10-Jan-2004 Title: "Line Intersection Demo" Purpose: {Demonstrate an algorithm used to detect an intersection between two line segments.} Library: [ level: 'intermediate platform: 'all type: [function FAQ] domain: [ui user-interface graphics gui animation] tested-under: [view 1.2.1.3.1 on W2K] support: none license: 'public-domain see-also: none ] Version: 1.0.0 Author: "Claude Precourt" Acknowledgements: ["Paul Bourke"] Web: http://astronomy.swin.edu.au/~pbourke/geometry/lineline2d/ ] line-intersect?: func [ pt1 [pair!] pt2 [pair!] pt3 [pair!] pt4 [pair!] /local denom ua ub ][ denom: ((pt4/y - pt3/y) * (pt2/x - pt1/x)) - ((pt4/x - pt3/x) * (pt2/y - pt1/y)) if denom = 0 [print "parallel" return false] ;; lines are parallel ua: (((pt4/x - pt3/x) * (pt1/y - pt3/y)) - ((pt4/y - pt3/y) * (pt1/x - pt3/x))) / denom ub: (((pt2/x - pt1/x) * (pt1/y - pt3/y)) - ((pt2/y - pt1/y) * (pt1/x - pt3/x))) / denom either (ua >= 0) and (ua <= 1) and (ub >= 0) and (ub <= 1) [return true][return false] ] img-data: to-image layout [origin 0x0 box black 512x512] view layout [ img: image img-data across button "Test" [ pt1: to-pair reduce [random 512 random 512] pt2: to-pair reduce [random 512 random 512] pt3: to-pair reduce [random 512 random 512] pt4: to-pair reduce [random 512 random 512] either line-intersect? pt1 pt2 pt3 pt4 [ pen-color: red status-text/text: "YES" ][ pen-color: white status-text/text: "NO" ] img-data: to-image layout [origin 0x0 box black 512x512 effect [ draw [pen pen-color line pt1 pt2 line pt3 pt4] ] ] img/image: img-data show [img status-text] ] button "Quit" [quit] text bold " Intersection?" status-text: text 150x24 "-" ]
halt ;; to terminate script if DO'ne from webpage