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1 | // Boost.Geometry (aka GGL, Generic Geometry Library) |
2 | ||
3 | // Copyright (c) 2007-2015 Barend Gehrels, Amsterdam, the Netherlands. | |
4 | ||
5 | // This file was modified by Oracle on 2015. | |
6 | // Modifications copyright (c) 2015 Oracle and/or its affiliates. | |
7 | ||
8 | // Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle | |
9 | ||
10 | // Use, modification and distribution is subject to the Boost Software License, | |
11 | // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
12 | // http://www.boost.org/LICENSE_1_0.txt) | |
13 | ||
14 | #ifndef BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_CLIP_LINESTRING_HPP | |
15 | #define BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_CLIP_LINESTRING_HPP | |
16 | ||
17 | #include <boost/range.hpp> | |
18 | ||
19 | #include <boost/geometry/algorithms/clear.hpp> | |
20 | #include <boost/geometry/algorithms/convert.hpp> | |
21 | ||
22 | #include <boost/geometry/algorithms/detail/overlay/append_no_duplicates.hpp> | |
23 | ||
24 | #include <boost/geometry/util/select_coordinate_type.hpp> | |
25 | #include <boost/geometry/geometries/segment.hpp> | |
26 | ||
27 | namespace boost { namespace geometry | |
28 | { | |
29 | ||
30 | namespace strategy { namespace intersection | |
31 | { | |
32 | ||
33 | /*! | |
34 | \brief Strategy: line clipping algorithm after Liang Barsky | |
35 | \ingroup overlay | |
36 | \details The Liang-Barsky line clipping algorithm clips a line with a clipping box. | |
37 | It is slightly adapted in the sense that it returns which points are clipped | |
38 | \tparam B input box type of clipping box | |
39 | \tparam P input/output point-type of segments to be clipped | |
40 | \note The algorithm is currently only implemented for 2D Cartesian points | |
41 | \note Though it is implemented in namespace strategy, and theoretically another | |
42 | strategy could be used, it is not (yet) updated to the general strategy concepts, | |
43 | and not (yet) splitted into a file in folder strategies | |
44 | \author Barend Gehrels, and the following recourses | |
45 | - A tutorial: http://www.skytopia.com/project/articles/compsci/clipping.html | |
46 | - a German applet (link broken): http://ls7-www.cs.uni-dortmund.de/students/projectgroups/acit/lineclip.shtml | |
47 | */ | |
48 | template<typename Box, typename Point> | |
49 | class liang_barsky | |
50 | { | |
51 | private: | |
52 | typedef model::referring_segment<Point> segment_type; | |
53 | ||
54 | template <typename CoordinateType, typename CalcType> | |
55 | inline bool check_edge(CoordinateType const& p, CoordinateType const& q, CalcType& t1, CalcType& t2) const | |
56 | { | |
57 | bool visible = true; | |
58 | ||
59 | if(p < 0) | |
60 | { | |
61 | CalcType const r = static_cast<CalcType>(q) / p; | |
62 | if (r > t2) | |
63 | visible = false; | |
64 | else if (r > t1) | |
65 | t1 = r; | |
66 | } | |
67 | else if(p > 0) | |
68 | { | |
69 | CalcType const r = static_cast<CalcType>(q) / p; | |
70 | if (r < t1) | |
71 | visible = false; | |
72 | else if (r < t2) | |
73 | t2 = r; | |
74 | } | |
75 | else | |
76 | { | |
77 | if (q < 0) | |
78 | visible = false; | |
79 | } | |
80 | ||
81 | return visible; | |
82 | } | |
83 | ||
84 | public: | |
85 | ||
86 | inline bool clip_segment(Box const& b, segment_type& s, bool& sp1_clipped, bool& sp2_clipped) const | |
87 | { | |
88 | typedef typename select_coordinate_type<Box, Point>::type coordinate_type; | |
89 | typedef typename select_most_precise<coordinate_type, double>::type calc_type; | |
90 | ||
91 | calc_type t1 = 0; | |
92 | calc_type t2 = 1; | |
93 | ||
94 | coordinate_type const dx = get<1, 0>(s) - get<0, 0>(s); | |
95 | coordinate_type const dy = get<1, 1>(s) - get<0, 1>(s); | |
96 | ||
97 | coordinate_type const p1 = -dx; | |
98 | coordinate_type const p2 = dx; | |
99 | coordinate_type const p3 = -dy; | |
100 | coordinate_type const p4 = dy; | |
101 | ||
102 | coordinate_type const q1 = get<0, 0>(s) - get<min_corner, 0>(b); | |
103 | coordinate_type const q2 = get<max_corner, 0>(b) - get<0, 0>(s); | |
104 | coordinate_type const q3 = get<0, 1>(s) - get<min_corner, 1>(b); | |
105 | coordinate_type const q4 = get<max_corner, 1>(b) - get<0, 1>(s); | |
106 | ||
107 | if (check_edge(p1, q1, t1, t2) // left | |
108 | && check_edge(p2, q2, t1, t2) // right | |
109 | && check_edge(p3, q3, t1, t2) // bottom | |
110 | && check_edge(p4, q4, t1, t2)) // top | |
111 | { | |
112 | sp1_clipped = t1 > 0; | |
113 | sp2_clipped = t2 < 1; | |
114 | ||
115 | if (sp2_clipped) | |
116 | { | |
117 | set<1, 0>(s, get<0, 0>(s) + t2 * dx); | |
118 | set<1, 1>(s, get<0, 1>(s) + t2 * dy); | |
119 | } | |
120 | ||
121 | if(sp1_clipped) | |
122 | { | |
123 | set<0, 0>(s, get<0, 0>(s) + t1 * dx); | |
124 | set<0, 1>(s, get<0, 1>(s) + t1 * dy); | |
125 | } | |
126 | ||
127 | return true; | |
128 | } | |
129 | ||
130 | return false; | |
131 | } | |
132 | ||
133 | template<typename Linestring, typename OutputIterator> | |
134 | inline void apply(Linestring& line_out, OutputIterator out) const | |
135 | { | |
136 | if (!boost::empty(line_out)) | |
137 | { | |
138 | *out = line_out; | |
139 | ++out; | |
140 | geometry::clear(line_out); | |
141 | } | |
142 | } | |
143 | }; | |
144 | ||
145 | ||
146 | }} // namespace strategy::intersection | |
147 | ||
148 | ||
149 | #ifndef DOXYGEN_NO_DETAIL | |
150 | namespace detail { namespace intersection | |
151 | { | |
152 | ||
153 | /*! | |
154 | \brief Clips a linestring with a box | |
155 | \details A linestring is intersected (clipped) by the specified box | |
156 | and the resulting linestring, or pieces of linestrings, are sent to the specified output operator. | |
157 | \tparam OutputLinestring type of the output linestrings | |
158 | \tparam OutputIterator an output iterator which outputs linestrings | |
159 | \tparam Linestring linestring-type, for example a vector of points, matching the output-iterator type, | |
160 | the points should also match the input-iterator type | |
161 | \tparam Box box type | |
162 | \tparam Strategy strategy, a clipping strategy which should implement the methods "clip_segment" and "apply" | |
163 | */ | |
164 | template | |
165 | < | |
166 | typename OutputLinestring, | |
167 | typename OutputIterator, | |
168 | typename Range, | |
169 | typename RobustPolicy, | |
170 | typename Box, | |
171 | typename Strategy | |
172 | > | |
173 | OutputIterator clip_range_with_box(Box const& b, Range const& range, | |
174 | RobustPolicy const&, | |
175 | OutputIterator out, Strategy const& strategy) | |
176 | { | |
177 | if (boost::begin(range) == boost::end(range)) | |
178 | { | |
179 | return out; | |
180 | } | |
181 | ||
182 | typedef typename point_type<OutputLinestring>::type point_type; | |
183 | ||
184 | OutputLinestring line_out; | |
185 | ||
186 | typedef typename boost::range_iterator<Range const>::type iterator_type; | |
187 | iterator_type vertex = boost::begin(range); | |
188 | for(iterator_type previous = vertex++; | |
189 | vertex != boost::end(range); | |
190 | ++previous, ++vertex) | |
191 | { | |
192 | point_type p1, p2; | |
193 | geometry::convert(*previous, p1); | |
194 | geometry::convert(*vertex, p2); | |
195 | ||
196 | // Clip the segment. Five situations: | |
197 | // 1. Segment is invisible, finish line if any (shouldn't occur) | |
198 | // 2. Segment is completely visible. Add (p1)-p2 to line | |
199 | // 3. Point 1 is invisible (clipped), point 2 is visible. Start new line from p1-p2... | |
200 | // 4. Point 1 is visible, point 2 is invisible (clipped). End the line with ...p2 | |
201 | // 5. Point 1 and point 2 are both invisible (clipped). Start/finish an independant line p1-p2 | |
202 | // | |
203 | // This results in: | |
204 | // a. if p1 is clipped, start new line | |
205 | // b. if segment is partly or completely visible, add the segment | |
206 | // c. if p2 is clipped, end the line | |
207 | ||
208 | bool c1 = false; | |
209 | bool c2 = false; | |
210 | model::referring_segment<point_type> s(p1, p2); | |
211 | ||
212 | if (!strategy.clip_segment(b, s, c1, c2)) | |
213 | { | |
214 | strategy.apply(line_out, out); | |
215 | } | |
216 | else | |
217 | { | |
218 | // a. If necessary, finish the line and add a start a new one | |
219 | if (c1) | |
220 | { | |
221 | strategy.apply(line_out, out); | |
222 | } | |
223 | ||
224 | // b. Add p1 only if it is the first point, then add p2 | |
225 | if (boost::empty(line_out)) | |
226 | { | |
227 | detail::overlay::append_no_duplicates(line_out, p1, true); | |
228 | } | |
229 | detail::overlay::append_no_duplicates(line_out, p2); | |
230 | ||
231 | // c. If c2 is clipped, finish the line | |
232 | if (c2) | |
233 | { | |
234 | strategy.apply(line_out, out); | |
235 | } | |
236 | } | |
237 | ||
238 | } | |
239 | ||
240 | // Add last part | |
241 | strategy.apply(line_out, out); | |
242 | return out; | |
243 | } | |
244 | ||
245 | }} // namespace detail::intersection | |
246 | #endif // DOXYGEN_NO_DETAIL | |
247 | ||
248 | }} // namespace boost::geometry | |
249 | ||
250 | #endif // BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_CLIP_LINESTRING_HPP |