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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.core.precision.DoublePrecisionContext;
    24  import org.apache.commons.geometry.core.precision.EpsilonDoublePrecisionContext;
    25  import org.apache.commons.geometry.euclidean.twod.Bounds2D;
    26  import org.apache.commons.geometry.euclidean.twod.Line;
    27  import org.apache.commons.geometry.euclidean.twod.Lines;
    28  import org.apache.commons.geometry.euclidean.twod.RegionBSPTree2D;
    29  import org.apache.commons.geometry.euclidean.twod.RegionBSPTree2D.RegionNode2D;
    30  import org.apache.commons.geometry.euclidean.twod.Vector2D;
    31
    32  /** Class containing tutorial code for constructing a 2D BSP tree using
    33   * a bottom-up approach.
    34   */
    35  public final class BottomUpBSPTreeConstruction {
    36
    37      /** String defining the name format of output svg files. */
    38      private static final String OUTPUT_FILE_FORMAT = "bu-cut-%d.svg";
    39
    40      /** No instantiation. */
    41      private BottomUpBSPTreeConstruction() {}
    42
    43      /** Tutorial code entry point.
    44       * @param args command arguments; if given, the first argument is used as the location of
    45       *      output folder
    46       */
    47      public static void main(String[] args) {
    48          File outputFolder = new File(args.length > 0 ? args[0] : ".");
    49          BSPTreeSVGWriter svgWriter = new BSPTreeSVGWriter(Bounds2D.from(Vector2D.of(-8, -8), Vector2D.of(8, 8)));
    50
    51          Map<RegionNode2D, String> nodeNames = new HashMap<>();
    52          int cutCount = -1;
    53
    54          // create a precision context for floating point comparisons
    55          DoublePrecisionContext precision = new EpsilonDoublePrecisionContext(1e-6);
    56
    57          // construct an empty tree
    58          RegionBSPTree2D tree = RegionBSPTree2D.empty();
    59
    60          Line rootCut = Lines.fromPointAndDirection(Vector2D.ZERO, Vector2D.Unit.PLUS_X, precision);
    61          RegionNode2D a = tree.getRoot();
    62
    63          nodeNames.put(a, "a");
    64          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    65
    66          // add a single cut
    67          a.cut(rootCut);
    68
    69          RegionNode2D b = a.getMinus();
    70          RegionNode2D c = a.getPlus();
    71
    72          nodeNames.put(b, "b");
    73          nodeNames.put(c, "c");
    74          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    75
    76          // add another cut
    77          b.insertCut(Lines.fromPoints(Vector2D.of(1, 0), Vector2D.of(-1, 1), precision));
    78
    79          RegionNode2D d = b.getMinus();
    80          RegionNode2D e = b.getPlus();
    81
    82          nodeNames.put(d, "d");
    83          nodeNames.put(e, "e");
    84          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    85
    86          d.insertCut(Lines.fromPointAndDirection(Vector2D.of(-5, 1), Vector2D.Unit.MINUS_Y, precision));
    87
    88          RegionNode2D f = d.getMinus();
    89          RegionNode2D g = d.getPlus();
    90
    91          nodeNames.put(f, "f");
    92          nodeNames.put(g, "g");
    93          svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    94
    95          // other side
    96          c.insertCut(Lines.fromPoints(Vector2D.of(-1, 0), Vector2D.of(1, -1), precision));
    97
    98          RegionNode2D h = c.getMinus();
    99          RegionNode2D i = c.getPlus();
    100
    101         nodeNames.put(h, "h");
    102         nodeNames.put(i, "i");
    103         svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    104
    105         h.insertCut(Lines.fromPointAndDirection(Vector2D.of(5, -1), Vector2D.Unit.PLUS_Y, precision));
    106
    107         RegionNode2D j = h.getMinus();
    108         RegionNode2D k = h.getPlus();
    109
    110         nodeNames.put(j, "j");
    111         nodeNames.put(k, "k");
    112         svgWriter.write(tree, nodeNames, new File(outputFolder, String.format(OUTPUT_FILE_FORMAT, ++cutCount)));
    113     }
    114 }