Class: Geometry::Polyline

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

Overview

A Polyline is like a Polygon in that it only contains straight lines, but also like a Path in that it isn’t necessarily closed.

http://en.wikipedia.org/wiki/Polyline

Usage

Direct Known Subclasses

Polygon

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(Edge, Edge, ...) ⇒ Polyline #initialize(Point, Point, ...) ⇒ Polyline

Construct a new Polyline from Points and/or Edges

The constructor will try to convert all of its arguments into {Point}s and
 {Edge}s. Then successive {Point}s will be collpased into {Edge}s. Successive
 {Edge}s that share a common vertex will be added to the new {Polyline}. If
 there's a gap between {Edge}s it will be automatically filled with a new
 {Edge}.

Overloads:

  • #initialize(Edge, Edge, ...) ⇒ Polyline
  • #initialize(Point, Point, ...) ⇒ Polyline 


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# File 'lib/geometry/polyline.rb', line 28

def initialize(*args)
    args.map! {|a| (a.is_a?(Array) || a.is_a?(Vector)) ? Point[a] : a}
    args.each {|a| raise ArgumentError, "Unknown argument type #{a.class}" unless a.is_a?(Point) or a.is_a?(Edge) }

    @edges = [];
    @vertices = [];

    first = args.shift
    if first.is_a?(Point)
	@vertices.push first
    elsif first.is_a?(Edge)
	@edges.push first
	@vertices.push *(first.to_a)
    end

    args.reduce(@vertices.last) do |previous,n|
	if n.is_a?(Point)
	    if n == previous	# Ignore repeated Points
		previous
	    else
		if @edges.last
		    new_edge = Edge.new(previous, n)
		    if @edges.last.parallel?(new_edge)
			popped_edge = @edges.pop		# Remove the previous Edge
			@vertices.pop(@edges.size ? 1 : 2)	# Remove the now unused vertex, or vertices
			if n == popped_edge.first
			    popped_edge.first
			else
			    push_edge Edge.new(popped_edge.first, n)
			    push_vertex popped_edge.first
			    push_vertex n
			    n
			end
		    else
			push_edge Edge.new(previous, n)
			push_vertex n
			n
		    end
		else
		    push_edge Edge.new(previous, n)
		    push_vertex n
		    n
		end
	    end
	elsif n.is_a?(Edge)
	    if previous == n.first
		push_edge n
		push_vertex n.last
	    elsif previous == n.last
		push_edge n.reverse!
		push_vertex n.last
	    else
		e = Edge.new(previous, n.first)
		push_edge e, n
		push_vertex *(e.to_a), *(n.to_a)
	    end
	    n.last
	end
    end
end

Instance Attribute Details

#edges ⇒ Object (readonly)

Returns the value of attribute edges.



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

def edges
  @edges
end

#vertices ⇒ Object (readonly)

Returns the value of attribute vertices.



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

def vertices
  @vertices
end

Instance Method Details

#eql?(other) ⇒ Bool Also known as: ==

Check the equality of two Geometry::Polylines. Note that if two Geometry::Polylines have

opposite winding, but are otherwise identical, they will be considered unequal.

Returns:



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# File 'lib/geometry/polyline.rb', line 92

def eql?(other)
    @vertices.zip(other.vertices).all? {|a,b| a == b}
end

#offset(distance) ⇒ Polygon Also known as: leftset

Offset the receiver by the specified distance. A positive distance

will offset to the left, and a negative distance to the right.

Parameters:

  • distance (Number) —

    The distance to offset by

Returns:



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# File 'lib/geometry/polyline.rb', line 101

def offset(distance)
    bisectors = offset_bisectors(distance)
    offsets = bisectors.each_cons(2).to_a

    # Create the offset edges and then wrap them in Hashes so the edges
    #  can be altered while walking the array
    active_edges = edges.zip(offsets).map do |e,offset|
	offset = Edge.new(e.first+offset.first.vector, e.last+offset.last.vector)

	# Skip zero-length edges
	{:edge => (offset.first == offset.last) ? nil : offset}
    end

    # Walk the array and handle any intersections
    for i in 0..(active_edges.count-1) do
	e1 = active_edges[i][:edge]
	next unless e1	# Ignore deleted edges

	intersection, j = find_last_intersection(active_edges, i, e1)
	if intersection
	    e2 = active_edges[j][:edge]
	    if intersection.is_a? Point
		active_edges[i][:edge] = Edge.new(e1.first, intersection)
		active_edges[j][:edge] = Edge.new(intersection, e2.last)
	    else
		# Handle the collinear case
		active_edges[i][:edge] = Edge.new(e1.first, e2.last)
		active_edges[j].delete(:edge)
	    end

	    # Delete everything between e1 and e2
	    for k in i..j do
		next if (k==i) or (k==j)    # Exclude e1 and e2
		active_edges[k].delete(:edge)
	    end

	    redo    # Recheck the modified edges
	end
    end
    Polyline.new *(active_edges.map {|e| e[:edge]}.compact.map {|e| [e.first, e.last]}.flatten)
end

#rightset(distance) ⇒ Polygon

Rightset the receiver by the specified distance

Parameters:

  • distance (Number) —

    The distance to offset by

Returns:



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# File 'lib/geometry/polyline.rb', line 147

def rightset(distance)
    offset(-distance)
end