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@etrepat
Created July 14, 2011 10:55
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Check if a given point is inside a triangle
# encoding: utf-8
require 'pp'
class Point
attr_accessor :x, :y
def initialize(x=0.0, y=0.0)
@x = x
@y = y
end
end
class Triangle
attr_accessor :points
def initialize(points=[])
@points = points
end
def area
compute_area(@points)
end
def inside?(point)
pab = compute_area([point, @points[0], @points[1]])
pbc = compute_area([point, @points[1], @points[2]])
pac = compute_area([point, @points[0], @points[2]])
(pab + pbc + pac) == area
end
private
# Finds the area of a polygon
# From: http://en.wikipedia.org/wiki/Polygon#Area_and_centroid
def compute_area(points)
c = points.last
area = 0
points.each do |point|
area += c.x * point.y - point.x * c.y
c = point
end
area.abs / 2.0
end
end
t = Triangle.new([Point.new(0,0), Point.new(10,10), Point.new(10, 0)])
pp t
pp t.inside?(Point.new(5,5)) # => true
pp t.inside?(Point.new(3,8)) # => false
t = Triangle.new([Point.new(0,0), Point.new(10, 0), Point.new(0, 0)])
pp t
pp t.inside?(Point.new(5,5)) # => false
pp t.inside?(Point.new(3,8)) # => false
pp t.inside?(Point.new(2,0)) # => true
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