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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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Copyright 1999-2004 The Apache Software Foundation
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you may not use this file except in compliance with the License.
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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.
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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN"
"http://cvs.apache.org/viewcvs.cgi/*checkout*/xml-forrest/src/resources/schema/dtd/document-v11.dtd">
<!-- $Id$ -->
<document>
<header>
<title>Layout managers</title>
<authors>
<person name="Peter B. West" email="pbwest@powerup.com.au"/>
</authors>
</header>
<body>
<section>
<title>Layout managers in FOP</title>
<p>
What do the layout managers do? Most layout is is "automatic"
in the sense of being a straightforward stacking operation.
Sibling inline-areas, including fo:character areas, are
stacked in line-areas in the inline-progression-direction.
Sibling block-areas, including line-areas, are stacked in the
block-progression-direction.
</p>
<p>
In the simple cases in which both the available
block-progression-dimension and the available
inline-progression-dimension are known, this process can be
driven bottom-up. Available dimensions trickle down from the
top, and the bottom level galleys can determine when their
available areas are full and suspend pending the arrival of
more areas. Such full notifications bubble back up the tree
of active galleys. E.g., if an inline galley fills a
line-area of a given inline-p-d and suspends while still
within the available block-p-d, the parent block-area galley
will simply stack the inline-area and notify the inline galley
to continue. If the inline-galley discovers that the next
line-area that it would generate will not fit in the the
block-p-d, it suspends with a notification to that effect to
its parent.
</p>
<p>
In more complex cases the dimensions may not be fully
specified, or decisions about layout may depend on later
layout. In all such cases some layout look-ahead is required
which can report results back to higher layout levels. The
job for a layout manager in these cirucmstances is to evaluate
the information flowing back and set parameters for the best
fit layout.
</p>
</section>
</body>
</document>
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