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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.Arrays;
    21  import java.util.HashMap;
    22  import java.util.Map;
    23
    24  import org.apache.commons.geometry.euclidean.twod.Bounds2D;
    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.Segment;
    29  import org.apache.commons.geometry.euclidean.twod.Vector2D;
    30  import org.apache.commons.geometry.euclidean.twod.path.LinePath;
    31  import org.apache.commons.numbers.core.Precision;
    32
    33  /** Class containing tutorial code for constructing a 2D BSP tree using
    34   * a top-down approach.
    35   */
    36  public final class TopDownBSPTreeConstruction {
    37
    38      /** String defining the name format of output svg files. */
    39      private static final String OUTPUT_FILE_FORMAT = "td-cut-%d.svg";
    40
    41      /** No instantiation. */
    42      private TopDownBSPTreeConstruction() {}
    43
    44      /** Tutorial code entry point.
    45       * @param args command arguments; if given, the first argument is used as the location of
    46       *      output folder
    47       */
    48      public static void main(final String[] args) {
    49          final File outputFolder = new File(args.length > 0 ? args[0] : ".");
    50          final BSPTreeSVGWriter svgWriter = new BSPTreeSVGWriter(Bounds2D.from(Vector2D.of(-8, -8), Vector2D.of(8, 8)));
    51
    52          final Map<RegionNode2D, String> nodeNames = new HashMap<>();
    53          int cutCount = 0;
    54
    55          // create a precision context for floating point comparisons
    56          final Precision.DoubleEquivalence precision = Precision.doubleEquivalenceOfEpsilon(1e-6);
    57
    58          // construct an empty tree
    59          final RegionBSPTree2D tree = RegionBSPTree2D.empty();
    60
    61          final Segment firstBoundary = Lines.segmentFromPoints(Vector2D.of(-5, 0), Vector2D.of(-1, 0), precision);
    62          tree.insert(firstBoundary);
    63
    64          final RegionNode2D a = tree.getRoot();
    65          final RegionNode2D b = a.getMinus();
    66          final RegionNode2D c = a.getPlus();
    67
    68          nodeNames.put(a, "a");
    69          nodeNames.put(b, "b");
    70          nodeNames.put(c, "c");
    71          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    72
    73          tree.insert(Lines.segmentFromPoints(Vector2D.of(1, 0), Vector2D.of(-5, 3), precision));
    74          tree.insert(Lines.segmentFromPoints(Vector2D.of(-5, 3), Vector2D.of(-5, 0), precision));
    75
    76          final RegionNode2D d = b.getMinus();
    77          final RegionNode2D e = b.getPlus();
    78          final RegionNode2D f = d.getMinus();
    79          final RegionNode2D g = d.getPlus();
    80
    81          nodeNames.put(d, "d");
    82          nodeNames.put(e, "e");
    83          nodeNames.put(f, "f");
    84          nodeNames.put(g, "g");
    85          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    86
    87          final LinePath path = LinePath.fromVertices(Arrays.asList(
    88                  Vector2D.of(-1, 0),
    89                  Vector2D.of(5, -3),
    90                  Vector2D.of(5, 0),
    91                  Vector2D.of(1, 0)), precision);
    92          tree.insert(path);
    93
    94          final RegionNode2D h = c.getMinus();
    95          final RegionNode2D i = c.getPlus();
    96          final RegionNode2D j = h.getMinus();
    97          final RegionNode2D k = h.getPlus();
    98
    99          nodeNames.put(h, "h");
    100         nodeNames.put(i, "i");
    101         nodeNames.put(j, "j");
    102         nodeNames.put(k, "k");
    103         svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    104     }
    105 }