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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
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/* $Id: LayoutManager.java 1562429 2014-01-29 12:52:26Z vhennebert $ */

package org.apache.fop.layoutmgr;

import java.util.List;
import java.util.Stack;

import org.apache.fop.area.Area;
import org.apache.fop.datatypes.PercentBaseContext;
import org.apache.fop.fo.FObj;

The interface for all LayoutManagers.
/**
 * The interface for all LayoutManagers.
 */
public interface LayoutManager extends PercentBaseContext {

    
Set the parent layout manager.
The parent layout manager is required for adding areas.
Params:
lm – the parent layout manager/**
     * Set the parent layout manager.
     * The parent layout manager is required for adding areas.
     *
     * @param lm the parent layout manager
     */
    void setParent(LayoutManager lm);

    
Get the parent layout manager.
Returns:
the parent layout manager./**
     * Get the parent layout manager.
     * @return the parent layout manager.
     */
    LayoutManager getParent();

    
initialize the layout manager. Allows each layout manager
to calculate often used values.
/**
     * initialize the layout manager. Allows each layout manager
     * to calculate often used values.
     */
    void initialize();

    
Get the active PageSequenceLayoutManager instance for this
layout process.
Returns:
the PageSequenceLayoutManager/**
     * Get the active PageSequenceLayoutManager instance for this
     * layout process.
     * @return the PageSequenceLayoutManager
     */
    PageSequenceLayoutManager getPSLM();

    
Return a value indicating whether this LayoutManager has laid out
all its content (or generated BreakPossibilities for all content.)
Returns:
true if this layout manager is finished/**
     * Return a value indicating whether this LayoutManager has laid out
     * all its content (or generated BreakPossibilities for all content.)
     *
     * @return true if this layout manager is finished
     */
    boolean isFinished();

    
Set a flag indicating whether the LayoutManager has laid out all
its content. This is generally called by the LM itself, but can
be called by a parentLM when backtracking.
Params:
isFinished – the value to set the finished flag to/**
     * Set a flag indicating whether the LayoutManager has laid out all
     * its content. This is generally called by the LM itself, but can
     * be called by a parentLM when backtracking.
     *
     * @param isFinished the value to set the finished flag to
     */
    void setFinished(boolean isFinished);

    
Get the parent area for an area.
This should get the parent depending on the class of the
area passed in.
Params:
childArea – the child area to get the parent for
Returns:
the parent Area/**
     * Get the parent area for an area.
     * This should get the parent depending on the class of the
     * area passed in.
     *
     * @param childArea the child area to get the parent for
     * @return the parent Area
     */
    Area getParentArea(Area childArea);

    
Add the area as a child of the current area.
This is called by child layout managers to add their
areas as children of the current area.
Params:
childArea – the child area to add/**
     * Add the area as a child of the current area.
     * This is called by child layout managers to add their
     * areas as children of the current area.
     *
     * @param childArea the child area to add
     */
    void addChildArea(Area childArea);

    
Tell the layout manager to add all the child areas implied
by Position objects which will be returned by the
Iterator.
Params:
posIter – the position iterator
context – the context/**
     * Tell the layout manager to add all the child areas implied
     * by Position objects which will be returned by the
     * Iterator.
     *
     * @param posIter the position iterator
     * @param context the context
     */
    void addAreas(PositionIterator posIter, LayoutContext context);

    
Create more child LMs of the parent, up to child LM index pos
Params:
pos – index up to which child LMs are requested
Returns:
true if requested index does exist/**
     * Create more child LMs of the parent, up to child LM index pos
     * @param pos index up to which child LMs are requested
     * @return true if requested index does exist
     */
    boolean createNextChildLMs(int pos);

    
Returns:
the list of child LMs/**
     * @return the list of child LMs
     */
    List getChildLMs();

    
Add the LM in the argument to the list of child LMs;
set this LM as the parent;
initialize the LM.
Params:
lm – the LM to be added/**
     * Add the LM in the argument to the list of child LMs;
     * set this LM as the parent;
     * initialize the LM.
     * @param lm the LM to be added
     */
    void addChildLM(LayoutManager lm);

    
Add the LMs in the argument to the list of child LMs;
Params:
newLMs – the list of LMs to be added/**
     * Add the LMs in the argument to the list of child LMs;
     * @param newLMs the list of LMs to be added
     */
    void addChildLMs(List newLMs);

    
Get a sequence of KnuthElements representing the content
of the node assigned to the LM.
Params:
context –   the LayoutContext used to store layout information
alignment – the desired text alignment
Returns:
         the list of KnuthElements/**
     * Get a sequence of KnuthElements representing the content
     * of the node assigned to the LM.
     *
     * @param context   the LayoutContext used to store layout information
     * @param alignment the desired text alignment
     * @return          the list of KnuthElements
     */
    List getNextKnuthElements(LayoutContext context, int alignment);

    
Get a sequence of KnuthElements representing the content
of the node assigned to the LM, after changes have been applied
In the context of line breaking, this method is called after hyphenation has
been performed, in order to receive the sequence of elements representing the
text together with all possible hyphenation points.
For example, if the text "representation" originates a single box element
when getNextKnuthElements() is called, it will be now split in syllables
(rep-re-sen-ta-tion) each one originating a box and divided by additional
elements allowing a line break.
In the context of page breaking, this method is called only if the pages need
to be "vertically justified" modifying (also) the quantity of lines created by
the paragraphs, and after a first page breaking has been performed.
According to the result of the first page breaking, each paragraph now knows
how many lines it must create (among the existing layout possibilities) and
has to create a sequence of elements representing this layout; in particular,
each box, representing a line, will contain a LineBreakPositions that will be
used in the addAreas() phase.
LMs having children look at the old list of elements in order to know which
ones they must get the new elements from, as break conditions of preserved
linefeeds can divide children into smaller groups (page sequences or
paragraphs).
LMs having no children can simply return the old elements if they have nothing
to change.
Inline LMs need to know the text alignment because it affects the elements
representing feasible breaks between syllables.
Params:
oldList –        the elements to replace
alignment –      the desired text alignment
Returns:
              the updated list of KnuthElements/**
     * Get a sequence of KnuthElements representing the content
     * of the node assigned to the LM, after changes have been applied
     *
     * In the context of line breaking, this method is called after hyphenation has
     * been performed, in order to receive the sequence of elements representing the
     * text together with all possible hyphenation points.
     * For example, if the text "representation" originates a single box element
     * when getNextKnuthElements() is called, it will be now split in syllables
     * (rep-re-sen-ta-tion) each one originating a box and divided by additional
     * elements allowing a line break.
     *
     * In the context of page breaking, this method is called only if the pages need
     * to be "vertically justified" modifying (also) the quantity of lines created by
     * the paragraphs, and after a first page breaking has been performed.
     * According to the result of the first page breaking, each paragraph now knows
     * how many lines it must create (among the existing layout possibilities) and
     * has to create a sequence of elements representing this layout; in particular,
     * each box, representing a line, will contain a LineBreakPositions that will be
     * used in the addAreas() phase.
     *
     * LMs having children look at the old list of elements in order to know which
     * ones they must get the new elements from, as break conditions of preserved
     * linefeeds can divide children into smaller groups (page sequences or
     * paragraphs).
     * LMs having no children can simply return the old elements if they have nothing
     * to change.
     *
     * Inline LMs need to know the text alignment because it affects the elements
     * representing feasible breaks between syllables.
     *
     * @param oldList        the elements to replace
     * @param alignment      the desired text alignment
     * @return               the updated list of KnuthElements
     */
    List getChangedKnuthElements(List oldList, int alignment);

    
Whether the FO handled by this layout manager has a descendant (including itself)
that will generate a line-area.
Returns:
true if a descendant line-area will be generated, false otherwise/**
     * Whether the FO handled by this layout manager has a descendant (including itself)
     * that will generate a line-area.
     *
     * @return {@code true} if a descendant line-area will be generated, {@code false} otherwise
     */
    boolean hasLineAreaDescendant();

    
Returns the position of the dominant-baseline of this FO's first descendant
line-area. 
The behavior of this method is undefined if this FO has no descendant line-area, and an exception may be thrown. See hasLineAreaDescendant()
See Also:
hasLineAreaDescendant()
Returns:
this FO's space-before plus the distance from the before-edge of its
allocation-rectangle to the dominant-baseline of the first line-area descendant/**
     * Returns the position of the dominant-baseline of this FO's first descendant
     * line-area. <p>The behavior of this method is undefined if this FO has no descendant
     * line-area, and an exception may be thrown. See {@link #hasLineAreaDescendant()}</p>
     *
     * @return this FO's space-before plus the distance from the before-edge of its
     * allocation-rectangle to the dominant-baseline of the first line-area descendant
     * @see #hasLineAreaDescendant()
     */
    int getBaselineOffset();

    
Returns the IPD of the content area
Returns:
the IPD of the content area/**
     * Returns the IPD of the content area
     * @return the IPD of the content area
     */
    int getContentAreaIPD();

    
Returns the BPD of the content area
Returns:
the BPD of the content area/**
     * Returns the BPD of the content area
     * @return the BPD of the content area
     */
    int getContentAreaBPD();

    
Returns an indication if the layout manager generates a reference area.
Returns:
True if the layout manager generates a reference area/**
     * Returns an indication if the layout manager generates a reference area.
     * @return True if the layout manager generates a reference area
     */
    boolean getGeneratesReferenceArea();

    
Returns an indication if the layout manager generates a block area.
Returns:
True if the layout manager generates a block area/**
     * Returns an indication if the layout manager generates a block area.
     * @return True if the layout manager generates a block area
     */
    boolean getGeneratesBlockArea();

    
Returns an indication if the layout manager generates a line area.
Returns:
True if the layout manager generates a line area/**
     * Returns an indication if the layout manager generates a line area.
     * @return True if the layout manager generates a line area
     */
    boolean getGeneratesLineArea();

    
Returns the fo this layout manager is associated with.
Returns:
The fo for this layout manager or null./**
     * Returns the fo this layout manager is associated with.
     * @return The fo for this layout manager or null.
     */
    FObj getFObj();

    
Adds a Position to the Position participating in the first|last determination by assigning
it a unique position index.
Params:
pos – the Position
Returns:
the same Position but with a position index/**
     * Adds a Position to the Position participating in the first|last determination by assigning
     * it a unique position index.
     * @param pos the Position
     * @return the same Position but with a position index
     */
    Position notifyPos(Position pos);

    
Re-initializes this layout manager in order to re-generate its Knuth
elements according to a new IPD value.
/**
     * Re-initializes this layout manager in order to re-generate its Knuth
     * elements according to a new IPD value.
     */
    void reset();

    
Returns true if this layout manager is able to re-generate its Knuth elements after an IPD change. 
Returns:
true if this layout manager can be restarted after an IPD change/**
     * Returns {@code true} if this layout manager is able to re-generate its
     * Knuth elements after an IPD change.
     *
     * @return {@code true} if this layout manager can be restarted after an IPD
     * change
     */
    boolean isRestartable();

    
Returns an updated list of Knuth elements corresponding to this layout
manager, after a change of IPD has been detected.
Params:
context – the layout context
alignment – the alignment
lmStack – the stack of LMs that are active at the IPD change
positionAtIPDChange – the position corresponding to the element
finishing the page before the IPD change
restartAtLM – if not null, the layout manager from which to restart.
That is, the IPD change occurs between two block elements and not inside
a paragraph
Returns:
an updated list of elements, taking the new IPD into account/**
     * Returns an updated list of Knuth elements corresponding to this layout
     * manager, after a change of IPD has been detected.
     *
     * @param context the layout context
     * @param alignment the alignment
     * @param lmStack the stack of LMs that are active at the IPD change
     * @param positionAtIPDChange the position corresponding to the element
     * finishing the page before the IPD change
     * @param restartAtLM if not null, the layout manager from which to restart.
     * That is, the IPD change occurs between two block elements and not inside
     * a paragraph
     * @return an updated list of elements, taking the new IPD into account
     */
    List getNextKnuthElements(LayoutContext context, int alignment, Stack lmStack,
            Position positionAtIPDChange, LayoutManager restartAtLM);
}