Class: WindingPolygon::SweepLine

Inherits:
Object
  • Object
show all
Defined in:
lib/winding-polygon/sweep_line.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(polygon) ⇒ SweepLine

Returns a new instance of SweepLine.



6
7
8
9
 
# File 'lib/winding-polygon/sweep_line.rb', line 6

def initialize(polygon)
  @tree    = AVLTree.new
  @polygon = polygon
end

Instance Attribute Details

#polygon ⇒ Object (readonly)

Returns the value of attribute polygon.



4
5
6
 
# File 'lib/winding-polygon/sweep_line.rb', line 4

def polygon
  @polygon
end

#tree ⇒ Object (readonly)

Returns the value of attribute tree.



3
4
5
 
# File 'lib/winding-polygon/sweep_line.rb', line 3

def tree
  @tree
end

Instance Method Details

#add(event) ⇒ Object 



11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
 
# File 'lib/winding-polygon/sweep_line.rb', line 11

def add(event)
  # build up segment data
  seg = Segment.new(event)
  p1 = @polygon.vertices[seg.edge]
  p2 = @polygon.vertices[seg.edge + 1]

  # if it is being added, then it must be a LEFT edge event
  # but need to determine which endpoint is the left one first

  if p1.compare(p2) < 0
    seg.left_point  = p1
    seg.right_point = p2
  else
    seg.left_point  = p2
    seg.right_point = p1
  end

  # Add node to tree and setup linkages to "above" and "below"
  # edges as per algorithm
  nd = @tree.insert(seg)

  nx = nd.next
  np = nd.prev

  if !nx.nil?
    seg.above = nx.value
    seg.above.below = seg
  end

  if !np.nil?
    seg.below = np.value
    seg.below.above = seg
  end
  return seg

end

#add_segment(seg) ⇒ Object 



48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
 
# File 'lib/winding-polygon/sweep_line.rb', line 48

def add_segment(seg)
  seg.below=seg.above=nil

  # Add node to tree and setup linkages to "above" and "below"
  # edges as per algorithm
  nd = @tree.insert(seg)

  nx = nd.next
  np = nd.prev

  if !nx.nil?
    seg.above = nx.value
    seg.above.below = seg
  end

  if !np.nil?
    seg.below = np.value
    seg.below.above = seg
  end
  return seg

end

#find(event) ⇒ Object 



71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
 
# File 'lib/winding-polygon/sweep_line.rb', line 71

def find(event)
  # need a segment to find it in the tree
  seg = Segment.new(event)
  p1 = @polygon.vertices[seg.edge]
  p2 = @polygon.vertices[seg.edge + 1]

  # if it is being added, then it must be a LEFT edge event
  # but need to determine which endpoint is the left one first
  if p1.compare(p2) < 0
    seg.left_point  = p1
    seg.right_point = p2
  else
    seg.left_point  = p2
    seg.right_point = p1
  end

  node = @tree.search(seg)

  return nil if node.nil?

  node.value
end

#find_segment(seg) ⇒ Object 



94
95
96
97
98
99
100
101
102
103
 
# File 'lib/winding-polygon/sweep_line.rb', line 94

def find_segment(seg)
  node = @tree.search(seg)

   if node.nil?
     node =  @tree.scan(seg)
     return nil if node.nil?
   end

  node.value
end

#intersect(s1, s2) ⇒ Object

test intersect of 2 segments and return: nil when none, point when intersecting



163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
 
# File 'lib/winding-polygon/sweep_line.rb', line 163

def intersect(s1,s2)
  # no intersect if either segment doesn't existend
  return nil if s1.nil? || s2.nil?

  # check for consecutive edges in polygon
  e1 = s1.edge
  e2 = s2.edge

  # no non-simple intersect since consecutive
  polygon_edges = @polygon.vertices.length-1
  return nil if (((e1+1)%polygon_edges === e2) || (e1 === (e2+1)%polygon_edges))


  #test for existence of an intersect point
  #s2 left point sign
  lsign = s2.left_point.is_left(s1.left_point, s1.right_point)
  #s2 right point sign
  rsign = s2.right_point.is_left(s1.left_point, s1.right_point)

  # s2 endpoints have same sign relative to s1  => on same side => no intersect is possible
  return nil if (lsign * rsign > 0)

  # s1 left point sign
  lsign = s1.left_point.is_left(s2.left_point, s2.right_point)
  #s1 right point sign
  rsign = s1.right_point.is_left(s2.left_point, s2.right_point)

  # s1 endpoints have same sign relative to s2 => on same side => no intersect is possible
  return nil  if (lsign * rsign > 0)

  #segments s1 and s2 straddle. Intersect exists.
  intersection_point = s1.intersection_point_with(s2)
  return nil if intersection_point.nil?
  intersection_point
end

#remove(seg) ⇒ Object 



105
106
107
108
109
110
111
112
113
114
115
116
 
# File 'lib/winding-polygon/sweep_line.rb', line 105

def remove(seg)
  nd = @tree.search(seg)
  return if nd.nil?

  nx = nd.next
  nx.value.below = seg.below if !nx.nil?

  np = nd.prev
  np.value.above = seg.above if !np.nil?

  @tree.delete(seg)
end

#swap(s1, s2) ⇒ Object 



118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
 
# File 'lib/winding-polygon/sweep_line.rb', line 118

def swap(s1,s2)
  nd1 = @tree.search(s1)
  return if nd1.nil?

  nd2 = @tree.search(s2)
  return if nd2.nil?


  nx1 = nd1.next
  nx1.value.below = nd2.value if !nx1.nil?

  np1 = nd1.prev
  np1.value.above = nd2.value if !np1.nil?

  nx2 = nd2.next
  nx2.value.below = nd1.value if !nx2.nil?

  np2 = nd2.prev
  np2.value.above = nd1.value if !np2.nil?


  nd1.value = s2
  nd2.value = s1

  temp = s1
  s1=s2
  s2=temp



  temp_above = s1.above
  temp_below = s1.below

  s1.above = s2.above
  s1.below = s2.below

  s2.above = temp_above
  s2.below = temp_below


  [s1,s2]

end