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/*
* Copyright 2005 The Apache Software Foundation.
*
* Licensed 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.traits.MinOptMax;
/**
* This is a the breaking algorithm that is responsible for balancing columns in multi-column
* layout.
*/
public class BalancingColumnBreakingAlgorithm extends PageBreakingAlgorithm {
private Log log = LogFactory.getLog(BalancingColumnBreakingAlgorithm.class);
private int columnCount;
private int fullLen;
private int idealPartLen;
public BalancingColumnBreakingAlgorithm(LayoutManager topLevelLM,
PageSequenceLayoutManager.PageViewportProvider pvProvider,
int alignment, int alignmentLast,
MinOptMax footnoteSeparatorLength,
boolean partOverflowRecovery,
int columnCount) {
super(topLevelLM, pvProvider, alignment, alignmentLast,
footnoteSeparatorLength, partOverflowRecovery);
this.columnCount = columnCount;
this.considerTooShort = true; //This is important!
}
/** @see org.apache.fop.layoutmgr.BreakingAlgorithm */
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);
//Step 1: This does the rough balancing
if (balance <= 0) {
dem = absBalance;
} else {
//shorter parts are less desired than longer ones
dem = absBalance * 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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