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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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