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- /*
- * 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.
- */
-
- /* $Id$ */
-
- package org.apache.fop.layoutmgr;
-
- import org.apache.commons.logging.Log;
- import org.apache.commons.logging.LogFactory;
-
- import org.apache.fop.fo.Constants;
- import org.apache.fop.traits.MinOptMax;
-
- /**
- * This is a the breaking algorithm that is responsible for balancing columns in multi-column
- * layout.
- */
- public class BalancingColumnBreakingAlgorithm extends PageBreakingAlgorithm {
-
- private static final Log LOG = LogFactory.getLog(BalancingColumnBreakingAlgorithm.class);
-
- private int columnCount;
- private int fullLen;
- private int idealPartLen;
-
- /**
- * Construct a balancing column breaking algorithm.
- * @param topLevelLM the top level layout manager
- * @param pageProvider the page provider
- * @param layoutListener the layout listener
- * @param alignment alignment of the paragraph/page. One of {@link Constants#EN_START},
- * {@link Constants#EN_JUSTIFY}, {@link Constants#EN_CENTER},
- * {@link Constants#EN_END}.
- * For pages, {@link Constants#EN_BEFORE} and {@link Constants#EN_AFTER}
- * are mapped to the corresponding inline properties,
- * {@link Constants#EN_START} and {@link Constants#EN_END}.
- * @param alignmentLast alignment of the paragraph's last line
- * @param footnoteSeparatorLength length of footnote separator
- * @param partOverflowRecovery {@code true} if too long elements should be moved to
- * the next line/part
- * @param columnCount number of columns
- * @see PageBreakingAlgorithm
- */
- public BalancingColumnBreakingAlgorithm( // CSOK: ParameterNumber
- LayoutManager topLevelLM,
- PageProvider pageProvider,
- PageBreakingLayoutListener layoutListener,
- int alignment, int alignmentLast,
- MinOptMax footnoteSeparatorLength,
- boolean partOverflowRecovery,
- int columnCount) {
- super(topLevelLM, pageProvider, layoutListener,
- alignment, alignmentLast,
- footnoteSeparatorLength, partOverflowRecovery, false, false);
- this.columnCount = columnCount;
- this.considerTooShort = true; //This is important!
- }
-
- /** {@inheritDoc} */
- protected double computeDemerits(KnuthNode activeNode,
- KnuthElement element, int fitnessClass, double r) {
- double dem = super.computeDemerits(activeNode, element, fitnessClass, r);
- if (LOG.isTraceEnabled()) {
- LOG.trace("original demerit=" + dem + " " + totalWidth
- + " line=" + activeNode.line + "/" + columnCount
- + " pos=" + activeNode.position + "/" + (par.size() - 1));
- }
- int remParts = columnCount - activeNode.line;
- int curPos = par.indexOf(element);
- if (fullLen == 0) {
- fullLen = ElementListUtils.calcContentLength(par, activeNode.position, par.size() - 1);
- this.idealPartLen = (fullLen / columnCount);
- }
- int partLen = ElementListUtils.calcContentLength(par, activeNode.position, curPos - 1);
- int restLen = ElementListUtils.calcContentLength(par, curPos - 1, par.size() - 1);
- int avgRestLen = 0;
- if (remParts > 0) {
- avgRestLen = restLen / remParts;
- }
- if (LOG.isTraceEnabled()) {
- LOG.trace("remaining parts: " + remParts + " rest len: " + restLen
- + " avg=" + avgRestLen);
- }
- double balance = (idealPartLen - partLen) / 1000f;
- if (LOG.isTraceEnabled()) {
- LOG.trace("balance=" + balance);
- }
- double absBalance = Math.abs(balance);
- dem = absBalance;
- //Step 1: This does the rough balancing
- if (columnCount > 2) {
- if (balance > 0) {
- //shorter parts are less desired than longer ones
- dem = dem * 1.2f;
- }
- } else {
- if (balance < 0) {
- //shorter parts are less desired than longer ones
- dem = dem * 1.2f;
- }
- }
- //Step 2: This helps keep the trailing parts shorter than the previous ones
- dem += (avgRestLen) / 1000f;
-
- if (activeNode.line >= columnCount) {
- //We don't want more columns than available
- dem = Double.MAX_VALUE;
- }
- if (LOG.isTraceEnabled()) {
- LOG.trace("effective dem=" + dem + " " + totalWidth);
- }
- return dem;
- }
- }
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