fop/src/java/org/apache/fop/layoutmgr/FlowLayoutManager.java

/*
 * Copyright 1999-2004 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.fop.fo.flow.Marker;
import org.apache.fop.area.Area;
import org.apache.fop.area.BlockParent;

import java.util.ArrayList;
import java.util.List;
import org.apache.fop.traits.MinOptMax;

/**
 * LayoutManager for an fo:flow object.
 * Its parent LM is the PageLayoutManager.
 * This LM is responsible for getting columns of the appropriate size
 * and filling them with block-level areas generated by its children.
 */
public class FlowLayoutManager extends BlockStackingLayoutManager {

    /** List of break possibilities */
    protected List blockBreaks = new ArrayList();

    /** Array of areas currently being filled stored by area class */
    private BlockParent[] currentAreas = new BlockParent[Area.CLASS_MAX];

    private int iStartPos = 0;

    /**
     * This is the top level layout manager.
     * It is created by the PageSequence FO.
     */
    public FlowLayoutManager() {
    }

    /**
     * @see org.apache.fop.layoutmgr.LayoutProcessor#getNextBreakPoss(LayoutContext)
     */
    public BreakPoss getNextBreakPoss(LayoutContext context) {

        // currently active LM
        LayoutProcessor curLM;
        MinOptMax stackSize = new MinOptMax();

        while ((curLM = getChildLM()) != null) {
            if (curLM.generatesInlineAreas()) {
                getLogger().error("inline area not allowed under flow - ignoring");
                curLM.setFinished(true);
                continue;
            }

            // Make break positions and return page break
            // Set up a LayoutContext
            MinOptMax bpd = context.getStackLimit();
            BreakPoss bp;

            LayoutContext childLC = new LayoutContext(0);
            boolean breakPage = false;
            childLC.setStackLimit(MinOptMax.subtract(bpd, stackSize));
            childLC.setRefIPD(context.getRefIPD());

            if (!curLM.isFinished()) {
                if ((bp = curLM.getNextBreakPoss(childLC)) != null) {
                    stackSize.add(bp.getStackingSize());
                    blockBreaks.add(bp);
                    // set stackLimit for remaining space
                    childLC.setStackLimit(MinOptMax.subtract(bpd, stackSize));

                    if (bp.isForcedBreak() || bp.nextBreakOverflows()) {
                        breakPage = true;
                    }
                }
            }

            // check the stack bpd and if greater than available
            // height then go to the last best break and return
            // break position
            if (stackSize.opt > context.getStackLimit().opt) {
                breakPage = true;
            }
            if (breakPage) {
                return new BreakPoss(
                      new LeafPosition(this, blockBreaks.size() - 1));
            }
        }
        setFinished(true);
        if (blockBreaks.size() > 0) {
            return new BreakPoss(
                             new LeafPosition(this, blockBreaks.size() - 1));
        }
        return null;
    }

    /**
     * @see org.apache.fop.layoutmgr.LayoutProcessor#addAreas(PositionIterator, LayoutContext)
     */
    public void addAreas(PositionIterator parentIter, LayoutContext layoutContext) {

        LayoutProcessor childLM;
        LayoutContext lc = new LayoutContext(0);
        while (parentIter.hasNext()) {
            LeafPosition lfp = (LeafPosition) parentIter.next();
            // Add the block areas to Area
            PositionIterator breakPosIter =
              new BreakPossPosIter(blockBreaks, iStartPos,
                                   lfp.getLeafPos() + 1);
            iStartPos = lfp.getLeafPos() + 1;
            while ((childLM = breakPosIter.getNextChildLM()) != null) {
                childLM.addAreas(breakPosIter, lc);
            }
        }

        flush();
    }

    /**
     * Add child area to a the correct container, depending on its
     * area class. A Flow can fill at most one area container of any class
     * at any one time. The actual work is done by BlockStackingLM.
     * @param childArea child area to add
     */
    public void addChild(Area childArea) {
        addChildToArea(childArea,
                          this.currentAreas[childArea.getAreaClass()]);
    }

    /**
     * @see org.apache.fop.layoutmgr.LayoutProcessor#getParentArea(Area)
     */
    public Area getParentArea(Area childArea) {
        // Get an area from the Page
        BlockParent parentArea =
          (BlockParent) parentLM.getParentArea(childArea);
        this.currentAreas[parentArea.getAreaClass()] = parentArea;
        setCurrentArea(parentArea);
        return parentArea;
    }

    /**
     * @see org.apache.fop.layoutmgr.LayoutProcessor#resetPosition(Position)
     */
    public void resetPosition(Position resetPos) {
        if (resetPos == null) {
            reset(null);
        }
    }

    /**
     * Retrieve marker is not allowed in the flow so this reports an
     * error and returns null.
     *
     * @see org.apache.fop.layoutmgr.LayoutManager
     */
    public Marker retrieveMarker(String name, int pos, int boundary) {
        // error cannot retrieve markers in flow
        getLogger().error("Cannot retrieve a marker from the flow");
        return null;
    }
}