Class: Geometry::Edge

Inherits:
Object
  • Object
show all
Defined in:
lib/geometry/edge.rb

Overview

An edge. It’s a line segment between 2 points. Generally part of a Polygon.

Usage

edge = Geometry::Edge([1,1], [2,2])

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(point0, point1) ⇒ Edge

Construct a new Geometry::Edge object from any two things that can be converted to a Point.



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# File 'lib/geometry/edge.rb', line 20

def initialize(point0, point1)
    @first, @last = [Point[point0], Point[point1]]
end

Instance Attribute Details

#direction ⇒ Vector (readonly)

Returns A unit Vector pointing from first to last.

Returns:



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# File 'lib/geometry/edge.rb', line 95

def direction
    @direction ||= self.vector.normalize
end

#first ⇒ Object (readonly)

Returns the value of attribute first.



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# File 'lib/geometry/edge.rb', line 16

def first
  @first
end

#last ⇒ Object (readonly)

Returns the value of attribute last.



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# File 'lib/geometry/edge.rb', line 16

def last
  @last
end

#vector ⇒ Vector (readonly)

Returns A Vector pointing from first to last.

Returns:



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# File 'lib/geometry/edge.rb', line 135

def vector
    @vector ||= last - first
end

Instance Method Details

#<=>(point) ⇒ Boolean

Returns 1 if the Point is strictly to the left of the receiver, -1 to the right, and 0 if the point is on the receiver

Parameters:

Returns:

  • (Boolean) —

    Returns 1 if the Point is strictly to the left of the receiver, -1 to the right, and 0 if the point is on the receiver



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# File 'lib/geometry/edge.rb', line 31

def <=>(point)
    case point
	when Point
	    k = (@last.x - @first.x) * (point.y - @first.y) - (point.x - @first.x) * (@last.y - @first.y)
	    if 0 == k
		(((@first.x <=> point.x) + (@last.x <=> point.x)).abs <= 1) && (((@first.y <=> point.y) + (@last.y <=> point.y)).abs <= 1) ? 0 : nil
	    else
		k <=> 0
	    end
	else
	    raise ArgumentError, "Can't spaceship with #{point.class}"
    end
end

#==(other) ⇒ Object

Two Edges are equal if both have equal Points in the same order



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# File 'lib/geometry/edge.rb', line 25

def ==(other)
    (@first == other.first) && (@last == other.last)
end

#connected?(other) ⇒ Bool

Returns true if the receiver and the passed Geometry::Edge share an endpoint

Parameters:

Returns:

  • (Bool) —

    Returns true if the receiver and the passed Geometry::Edge share an endpoint



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# File 'lib/geometry/edge.rb', line 89

def connected?(other)
    (@first == other.last) || (@last == other.first) || (@first == other.first) || (@last == other.last)
end

#height ⇒ Object

Return the Geometry::Edge‘s length along the Y axis



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# File 'lib/geometry/edge.rb', line 57

def height
    (@first.y - @last.y).abs
end

#inspect ⇒ Object Also known as: to_s 



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# File 'lib/geometry/edge.rb', line 66

def inspect
    'Edge(' + @first.inspect + ', ' + @last.inspect + ')'
end

#intersection(other) ⇒ Point

Find the intersection of two Geometry::Edges (bloggingmath.wordpress.com/2009/05/29/line-segment-intersection/)

Parameters:

Returns:

  • (Point) —

    The intersection of the two Geometry::Edges, nil if they don’t intersect, true if they’re collinear and overlapping, and false if they’re collinear and non-overlapping



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# File 'lib/geometry/edge.rb', line 102

def intersection(other)
    return self.first if (self.first == other.first) or (self.first == other.last)
    return self.last if (self.last == other.first) or (self.last == other.last)

    p0, p1 = self.first, self.last
    p2, p3 = other.first, other.last
    v1, v2 = self.vector, other.vector

    denominator = v1[0] * v2[1] - v2[0] * v1[1]		# v1 x v2
    p = p0 - p2
    if denominator == 0	    # collinear, so check for overlap
	if 0 == (-v1[1] * p.x + v1[0] * p.y)	# collinear?
	    # The edges are collinear, but do they overlap?
	    # Project them onto the x and y axes to find out
	    left1, right1 = [self.first[0], self.last[0]].sort
	    bottom1, top1 = [self.first[1], self.last[1]].sort
	    left2, right2 = [other.first[0], other.last[0]].sort
	    bottom2, top2 = [other.first[1], other.last[1]].sort

	    !((left2 > right1) || (right2 < left1) || (top2 < bottom1) || (bottom2 > top1))
	else
	    nil
	end
    else
	s = (-v1[1] * p.x + v1[0] * p.y) / denominator	# v1 x (p0 - p2) / denominator
	t = ( v2[0] * p.y - v2[1] * p.x) / denominator	# v2 x (p0 - p2) / denominator

	p0 + v1 * t if ((0..1) === s) && ((0..1) === t)
    end
end

#parallel?(edge) ⇒ Bool

Returns true if the passed Geometry::Edge is parallel to the receiver

Returns:

  • (Bool) —

    Returns true if the passed Geometry::Edge is parallel to the receiver



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# File 'lib/geometry/edge.rb', line 72

def parallel?(edge)
    v1 = self.direction
    v2 = edge.direction
    winding = v1[0]*v2[1] - v1[1]*v2[0]
    if 0 == winding	# collinear?
	if v1 == v2
	    1		# same direction
	else
	    -1		# opposite direction
	end
    else
	false
    end
end

#reverse ⇒ Object

Return a new Geometry::Edge with swapped endpoints



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# File 'lib/geometry/edge.rb', line 46

def reverse
    Edge.new(@last, @first)
end

#reverse! ⇒ Object

In-place swap the endpoints



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# File 'lib/geometry/edge.rb', line 51

def reverse!
    @first, @last = @last, @first
    self
end

#to_a ⇒ Object 



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# File 'lib/geometry/edge.rb', line 139

def to_a
    [@first, @last]
end

#width ⇒ Object

Return the Geometry::Edge‘s length along the X axis



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# File 'lib/geometry/edge.rb', line 62

def width
    (@first.x - @last.x).abs
end