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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.geometry.examples.tutorials.bsp;
18  
19  import java.io.File;
20  import java.util.HashMap;
21  import java.util.Map;
22  
23  import org.apache.commons.geometry.euclidean.twod.Bounds2D;
24  import org.apache.commons.geometry.euclidean.twod.Line;
25  import org.apache.commons.geometry.euclidean.twod.Lines;
26  import org.apache.commons.geometry.euclidean.twod.RegionBSPTree2D;
27  import org.apache.commons.geometry.euclidean.twod.RegionBSPTree2D.RegionNode2D;
28  import org.apache.commons.geometry.euclidean.twod.Vector2D;
29  import org.apache.commons.numbers.core.Precision;
30  
31  /** Class containing tutorial code for constructing a 2D BSP tree using
32   * a bottom-up approach.
33   */
34  public final class BottomUpBSPTreeConstruction {
35  
36      /** String defining the name format of output svg files. */
37      private static final String OUTPUT_FILE_FORMAT = "bu-cut-%d.svg";
38  
39      /** No instantiation. */
40      private BottomUpBSPTreeConstruction() {}
41  
42      /** Tutorial code entry point.
43       * @param args command arguments; if given, the first argument is used as the location of
44       *      output folder
45       */
46      public static void main(final String[] args) {
47          final File outputFolder = new File(args.length > 0 ? args[0] : ".");
48          final BSPTreeSVGWriter svgWriter = new BSPTreeSVGWriter(Bounds2D.from(Vector2D.of(-8, -8), Vector2D.of(8, 8)));
49  
50          final Map<RegionNode2D, String> nodeNames = new HashMap<>();
51          int cutCount = -1;
52  
53          // create a precision context for floating point comparisons
54          final Precision.DoubleEquivalence precision = Precision.doubleEquivalenceOfEpsilon(1e-6);
55  
56          // construct an empty tree
57          final RegionBSPTree2D tree = RegionBSPTree2D.empty();
58  
59          final Line rootCut = Lines.fromPointAndDirection(Vector2D.ZERO, Vector2D.Unit.PLUS_X, precision);
60          final RegionNode2D a = tree.getRoot();
61  
62          nodeNames.put(a, "a");
63          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
64  
65          // add a single cut
66          a.cut(rootCut);
67  
68          final RegionNode2D b = a.getMinus();
69          final RegionNode2D c = a.getPlus();
70  
71          nodeNames.put(b, "b");
72          nodeNames.put(c, "c");
73          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
74  
75          // add another cut
76          b.insertCut(Lines.fromPoints(Vector2D.of(1, 0), Vector2D.of(-1, 1), precision));
77  
78          final RegionNode2D d = b.getMinus();
79          final RegionNode2D e = b.getPlus();
80  
81          nodeNames.put(d, "d");
82          nodeNames.put(e, "e");
83          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
84  
85          d.insertCut(Lines.fromPointAndDirection(Vector2D.of(-5, 1), Vector2D.Unit.MINUS_Y, precision));
86  
87          final RegionNode2D f = d.getMinus();
88          final RegionNode2D g = d.getPlus();
89  
90          nodeNames.put(f, "f");
91          nodeNames.put(g, "g");
92          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
93  
94          // other side
95          c.insertCut(Lines.fromPoints(Vector2D.of(-1, 0), Vector2D.of(1, -1), precision));
96  
97          final RegionNode2D h = c.getMinus();
98          final RegionNode2D i = c.getPlus();
99  
100         nodeNames.put(h, "h");
101         nodeNames.put(i, "i");
102         svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
103 
104         h.insertCut(Lines.fromPointAndDirection(Vector2D.of(5, -1), Vector2D.Unit.PLUS_Y, precision));
105 
106         final RegionNode2D j = h.getMinus();
107         final RegionNode2D k = h.getPlus();
108 
109         nodeNames.put(j, "j");
110         nodeNames.put(k, "k");
111         svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
112     }
113 }