AbstractBSPTreeMergeOperator.java
- /*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- package org.apache.commons.geometry.core.partitioning.bsp;
- import org.apache.commons.geometry.core.Point;
- import org.apache.commons.geometry.core.partitioning.bsp.AbstractBSPTree.AbstractNode;
- /** Class containing the basic algorithm for merging two {@link AbstractBSPTree}
- * instances. Subclasses must override the
- * {@link #mergeLeaf(AbstractBSPTree.AbstractNode, AbstractBSPTree.AbstractNode)} method
- * to implement the merging logic for their particular use case. The remainder of the
- * algorithm is independent of the use case.
- *
- * <p>This class does not expose any public methods so that subclasses can present their own
- * public API, tailored to the specific types being worked with. In particular, most subclasses
- * will want to restrict the tree types used with the algorithm, which is difficult to implement
- * cleanly at this level.</p>
- *
- * <p>This class maintains state during the merging process and is therefore
- * <em>not</em> thread-safe.</p>
- * @param <P> Point implementation type
- * @param <N> BSP tree node implementation type
- */
- public abstract class AbstractBSPTreeMergeOperator<P extends Point<P>, N extends AbstractNode<P, N>> {
- /** The tree that the merge operation output will be written to. All existing content
- * in this tree is overwritten.
- */
- private AbstractBSPTree<P, N> outputTree;
- /** Set the tree used as output for this instance.
- * @param outputTree the tree used as output for this instance
- */
- protected void setOutputTree(final AbstractBSPTree<P, N> outputTree) {
- this.outputTree = outputTree;
- }
- /** Get the tree used as output for this instance.
- * @return the tree used as output for this instance
- */
- protected AbstractBSPTree<P, N> getOutputTree() {
- return outputTree;
- }
- /** Perform a merge operation with the two input trees and store the result in the output tree. The
- * output tree may be one of the input trees, in which case, the tree is modified in place.
- * @param input1 first input tree
- * @param input2 second input tree
- * @param output output tree all previous content in this tree is overwritten
- */
- protected void performMerge(final AbstractBSPTree<P, N> input1, final AbstractBSPTree<P, N> input2,
- final AbstractBSPTree<P, N> output) {
- setOutputTree(output);
- final N root1 = input1.getRoot();
- final N root2 = input2.getRoot();
- final N outputRoot = performMergeRecursive(root1, root2);
- getOutputTree().setRoot(outputRoot);
- }
- /** Recursively merge two nodes.
- * @param node1 node from the first input tree
- * @param node2 node from the second input tree
- * @return a merged node
- */
- private N performMergeRecursive(final N node1, final N node2) {
- if (node1.isLeaf() || node2.isLeaf()) {
- // delegate to the mergeLeaf method if we can no longer continue
- // merging recursively
- final N merged = mergeLeaf(node1, node2);
- // copy the merged node to the output if needed (in case mergeLeaf
- // returned one of the input nodes directly)
- return outputTree.importSubtree(merged);
- } else {
- final N partitioned = outputTree.splitSubtree(node2, node1.getCut());
- final N minus = performMergeRecursive(node1.getMinus(), partitioned.getMinus());
- final N plus = performMergeRecursive(node1.getPlus(), partitioned.getPlus());
- final N outputNode = outputTree.copyNode(node1);
- outputNode.setSubtree(node1.getCut(), minus, plus);
- return outputNode;
- }
- }
- /** Create a new node in the output tree. The node is associated with the output tree but
- * is not attached to a parent node.
- * @return a new node associated with the output tree but not yet attached to a parent
- */
- protected N outputNode() {
- return outputTree.createNode();
- }
- /** Place the subtree rooted at the given input node into the output tree. The subtree
- * is copied if needed.
- * @param node the root of the subtree to copy
- * @return a subtree in the output tree
- */
- protected N outputSubtree(final N node) {
- return outputTree.importSubtree(node);
- }
- /** Merge a leaf node from one input with a subtree from another.
- * <p>When this method is called, one or both of the given nodes will be a leaf node.
- * This method is expected to return a node representing the merger of the two given
- * nodes. The way that the returned node is determined defines the overall behavior of
- * the merge operation.
- * </p>
- * <p>The return value can be one of the two input nodes or a completely different one.</p>
- * @param node1 node from the first input tree
- * @param node2 node from the second input tree
- * @return node representing the merger of the two input nodes
- */
- protected abstract N mergeLeaf(N node1, N node2);
- }