001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.geometry.core.partitioning.bsp; 018 019import org.apache.commons.geometry.core.Point; 020import org.apache.commons.geometry.core.partitioning.bsp.AbstractBSPTree.AbstractNode; 021 022/** Class containing the basic algorithm for merging two {@link AbstractBSPTree} 023 * instances. Subclasses must override the 024 * {@link #mergeLeaf(AbstractBSPTree.AbstractNode, AbstractBSPTree.AbstractNode)} method 025 * to implement the merging logic for their particular use case. The remainder of the 026 * algorithm is independent of the use case. 027 * 028 * <p>This class does not expose any public methods so that subclasses can present their own 029 * public API, tailored to the specific types being worked with. In particular, most subclasses 030 * will want to restrict the tree types used with the algorithm, which is difficult to implement 031 * cleanly at this level.</p> 032 * 033 * <p>This class maintains state during the merging process and is therefore 034 * <em>not</em> thread-safe.</p> 035 * @param <P> Point implementation type 036 * @param <N> BSP tree node implementation type 037 */ 038public abstract class AbstractBSPTreeMergeOperator<P extends Point<P>, N extends AbstractNode<P, N>> { 039 040 /** The tree that the merge operation output will be written to. All existing content 041 * in this tree is overwritten. 042 */ 043 private AbstractBSPTree<P, N> outputTree; 044 045 /** Set the tree used as output for this instance. 046 * @param outputTree the tree used as output for this instance 047 */ 048 protected void setOutputTree(final AbstractBSPTree<P, N> outputTree) { 049 this.outputTree = outputTree; 050 } 051 052 /** Get the tree used as output for this instance. 053 * @return the tree used as output for this instance 054 */ 055 protected AbstractBSPTree<P, N> getOutputTree() { 056 return outputTree; 057 } 058 059 /** Perform a merge operation with the two input trees and store the result in the output tree. The 060 * output tree may be one of the input trees, in which case, the tree is modified in place. 061 * @param input1 first input tree 062 * @param input2 second input tree 063 * @param output output tree all previous content in this tree is overwritten 064 */ 065 protected void performMerge(final AbstractBSPTree<P, N> input1, final AbstractBSPTree<P, N> input2, 066 final AbstractBSPTree<P, N> output) { 067 068 setOutputTree(output); 069 070 final N root1 = input1.getRoot(); 071 final N root2 = input2.getRoot(); 072 073 final N outputRoot = performMergeRecursive(root1, root2); 074 075 getOutputTree().setRoot(outputRoot); 076 } 077 078 /** Recursively merge two nodes. 079 * @param node1 node from the first input tree 080 * @param node2 node from the second input tree 081 * @return a merged node 082 */ 083 private N performMergeRecursive(final N node1, final N node2) { 084 085 if (node1.isLeaf() || node2.isLeaf()) { 086 // delegate to the mergeLeaf method if we can no longer continue 087 // merging recursively 088 final N merged = mergeLeaf(node1, node2); 089 090 // copy the merged node to the output if needed (in case mergeLeaf 091 // returned one of the input nodes directly) 092 return outputTree.importSubtree(merged); 093 } else { 094 final N partitioned = outputTree.splitSubtree(node2, node1.getCut()); 095 096 final N minus = performMergeRecursive(node1.getMinus(), partitioned.getMinus()); 097 098 final N plus = performMergeRecursive(node1.getPlus(), partitioned.getPlus()); 099 100 final N outputNode = outputTree.copyNode(node1); 101 outputNode.setSubtree(node1.getCut(), minus, plus); 102 103 return outputNode; 104 } 105 } 106 107 /** Create a new node in the output tree. The node is associated with the output tree but 108 * is not attached to a parent node. 109 * @return a new node associated with the output tree but not yet attached to a parent 110 */ 111 protected N outputNode() { 112 return outputTree.createNode(); 113 } 114 115 /** Place the subtree rooted at the given input node into the output tree. The subtree 116 * is copied if needed. 117 * @param node the root of the subtree to copy 118 * @return a subtree in the output tree 119 */ 120 protected N outputSubtree(final N node) { 121 return outputTree.importSubtree(node); 122 } 123 124 /** Merge a leaf node from one input with a subtree from another. 125 * <p>When this method is called, one or both of the given nodes will be a leaf node. 126 * This method is expected to return a node representing the merger of the two given 127 * nodes. The way that the returned node is determined defines the overall behavior of 128 * the merge operation. 129 * </p> 130 * <p>The return value can be one of the two input nodes or a completely different one.</p> 131 * @param node1 node from the first input tree 132 * @param node2 node from the second input tree 133 * @return node representing the merger of the two input nodes 134 */ 135 protected abstract N mergeLeaf(N node1, N node2); 136}