keiron 2002/11/29 01:18:23
Added: src/documentation/content/xdocs/design/understanding
area_tree.xml book.xml fo_tree.xml images.xml
index.xml layout_managers.xml pdf_library.xml
properties.xml renderers.xml svg.xml
xml_parsing.xml
Log:
converted across understanding docs
Revision Changes Path
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/area_tree.xml
Index: area_tree.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>Area Tree</title>
</header>
<body>
<section>
<title>Area Tree</title>
<section>
<title>Area Tree</title>
<p>The Area Tree is an internal representation of the result document. This
is a set of java classes that can put together a set of objects that
represent the pages and their contents.</p>
<p>This information is created by the layout managers and is rendered to the
output using a renderer.</p>
<p>The Area Tree follows the description of the area tree in the XSL:FO
specification.</p>
<p>The Area Tree consists of a set of pages, the actual implemenation places
these in
a set of page sequences.</p>
</section>
<section>
<title>Pages</title>
<p>A page consists of a page+viewport pair.</p>
<p>The PageViewPort and Page with the regions is created by the
LayoutMasterSet. The contents are then placed by the layout managers. Once
the layout of a page is complete then it is added to the Area Tree.</p>
<p>Inside the page is a set of RegionViewport+Region pairs for each region on
the page.</p></section>
<section>
<title>Blocks</title>
<p>Block level areas contain either other blocks or line areas (which is a
special block area).</p><p>
A block is either positoned or stacked with other block areas.</p>
</section>
<section>
<title>Inline Areas</title>
<p>Inline areas are stacked in a line area. Inline areas are objects such as
character, viewport, inline-container, leader and space. A special inline
area Word is also used for a group of consecutive characters.</p>
<p>The image and instream foreign object areas are placed inside a viewport.
The leader (with use content) and unresolved page number areas are
resolved to other inline areas.</p>
<p>Once a LineArea is filled with inline areas then the inline areas need to
be aligned and adjusted to fill the line properly.</p>
</section>
<section>
<title>Traits</title>
<p>A trait is information associated with an area. This could be information
such as text colour or is-first.</p>
<p>Traits provide information about an area. The traits are derived from
properties on the formatting object or are generated during the layout
process. Many of the layout traits do not have actual values but can be
derived from the Area Tree. Other traits that apply when rendering the
areas are set on the area. Since setting the same value on every area
would use a lot of memory then the traits are derived from default or
parent values.</p>
<p>A dominant trait on a block area is set, for example font colour, so that
every line area with the same dominant value can derive it. The text
inline areas then get the font colour set on the inline area or from the
line area or from the block area.</p>
</section>
<section>
<title>Forward References</title>
<p>The Area Tree maintains a set of mappings from the reference to pages.</p>
<p>The PageViewPort holds the list of forward references that need resolving
so that if a references is resolved during layout the page can be easily
found and then fixed. Once all the forward references are resolved then
the page is ready to be rendered.</p>
<p>To layout a page any areas that cannot be resolved need to reserve space.
Once the inline area is resolved then the complete line should be adjusted
to accomodate any change in space used by the area.</p>
</section>
<section>
<title>Caching</title>
<p>We may need to cache pages due to forward references or when keeping all
pages.</p>
<p>This is done by serializing the Page. The PageViewport is retained to be
used as a key for page references and backward references.
The Page is serialized to an object stream and then all of the page
contents are released. The Page is then recoved by reading from the object
stream.</p>
<p>The PageViewport retains information about id areas for easy access.</p>
</section>
<section>
<title>Extensions</title>
<p>The Area Tree holds the Output Document extensions. This is information
such as pdf bookmarks or other output document specific information that
is not handled by XSL:FO.</p>
<p>It is also possible to create custom areas that extend a normal area. The
actual data that is rendered could be set in a different way or depend on
resolving a forward reference.</p>
</section>
<section>
<title>Area Tree Handlers</title>
<p>To handle different situations the handler for the Area Tree handles each
page as it is added.</p><p>
The RenderPagesModel sends the page directly to the renderer if the page
is ready to be rendered. Once a page is rendered it is discarded.
The StorePagesModel stores all the pages so that any page can be later
accessed.</p>
<p>The Area Tree retains the concept of page sequences (this is not in the
area tree in the spec) so that this information can be passed to the
renderer. This is useful for setting the title and organising the groups
of page sequences.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/book.xml
Index: book.xml
===================================================================
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//APACHE//DTD Cocoon Documentation Book V1.0//EN"
"http://cvs.apache.org/viewcvs.cgi/*checkout*/xml-cocoon2/src/documentation/xdocs/dtd/book-cocoon-v10.dtd";>
<book software="FOP"
title="Understanding FOP Design"
copyright="@year@ The Apache Software Foundation"
xmlns:xlink="http://www.w3.org/1999/xlink";>
<menu label="Index">
<menu-item label="FOP Home" href="../../index.html"/>
</menu>
<menu label="Understanding the Design">
<menu-item label="Understanding" href="index.html"/>
<menu-item label="XML Parsing" href="xml_parsing.html"/>
<menu-item label="FO Tree" href="fo_tree.html"/>
<menu-item label="Properties" href="properties.html"/>
<menu-item label="Layout Managers" href="layout_managers.html"/>
<menu-item label="Area Tree" href="area_tree.html"/>
<menu-item label="Renderers" href="renderers.html"/>
</menu>
<menu label="Extras">
<menu-item label="Images" href="images.html"/>
<menu-item label="PDF Library" href="pdf_library.html"/>
<menu-item label="SVG" href="svg.html"/>
</menu>
</book>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/fo_tree.xml
Index: fo_tree.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>FO Tree</title>
</header>
<body>
<section>
<title>FO Tree</title>
<p>
The FO Tree is a representation of the XSL:FO document. This
represents the <strong>Objectify</strong> step from the
spec. The <strong>Refinement</strong> step is part of reading
and using the properties which may happen immediately or
during the layout process.
</p>
<p>Each xml element is represented by a java object. For pagination the
classes are in <code>org.apache.fop.fo.pagination.*</code>, for elements in the flow
they are in <code>org.apache.fop.fo.flow.*</code> and some others are in
<code>org.apache.fop.fo.*.</code></p>
<p>The base class for all objects in the tree is FONode. The base class for
all FO Objects is FObj.</p>
<p>There is a class for each element in the FO set. An object is created for
each element in the FO Tree. This object holds the properties for the FO
Object.</p>
<p>
When the object is created it is setup. It is given its
element name, the FOUserAgent - for resolving properties
etc. - the logger and the attributes. The methods
<code>handleAttributes()</code> and
<code>setuserAgent()</code>, common to <code>FONode</code>,
are used in this process. The object will then be given any
text data or child elements. Then the <code>end()</code>
method is called. The end method is used by a number of
elements to indicate that it can do certain processing since
all the children have been added.
</p>
<p>Some validity checking is done during these steps. The user can be warned of the
error and processing can continue if possible.
</p>
<p>
The FO Tree is simply a heirarchy of java objects that
represent the fo elements from xml. The traversal is done by
the layout or structure process only in the flow elements.
</p>
<section>
<title>Properties</title>
<p>The XML attributes on each element are passed to the object. The objects
that represent FO objects then convert the attributes into properties.
</p>
<p>Since properties can be inherited the PropertyList class handles resolving
properties for a particular element.
All properties are specified in an XML file. Classes are created
automatically during the build process.
</p>
<p>In some cases the element may be moved to have a different parent, for
example markers, or the inheritance could be different, for example
initial property set.</p>
</section>
<section>
<title>Foreign XML</title>
<p>The base class for foreign XML is XMLObj. This class handles creating a
DOM Element and the setting of attributes. It also can create a DOM
Document if it is a top level element, class XMLElement.
This class must be extended for the namespace of the XML elements. For
unknown namespaces the class is UnknowXMLObj.</p>
<p>If some special processing is needed then the top level element can extend
the XMLObj. For example the SVGElement makes the special DOM required for
batik and gets the size of the svg.
</p>
<p>Foreign XML will usually be in an fo:instream-foreign-object, the XML will
be passed to the render as a DOM where the render will be able to handle
it. Other XML from an unknwon namespace will be ignored.
</p>
<p>By using element mappings it is possible to read other XML and either</p>
<ul><li>set information on the area tree</li>
<li>create pseudo FO Objects that create areas in the area tree</li>
<li>create FO Objects</li></ul>
</section>
<section>
<title>Unknown Elements</title>
<p>If an element is in a known namespace but the element is unknown then an
Unknown object is created. This is mainly to provide information to the
user.
This could happen if the fo document contains an element from a different
version or the element is misspelt.</p>
</section>
<section>
<title>Page Masters</title>
<p>
The first elements in a document are the elements for the
page master setup. This is usually only a small number and
will be used throughout the document to create new pages.
These elements are kept as a factory to create the page and
appropriate regions whenever a new page is requested by the
layout. The objects in the FO Tree that represent these
elements are themselves the factory. The root element keeps
these objects as a factory for the page sequences.
</p>
</section>
<section>
<title>Flow</title>
<p>The elements that are in the flow of the document are a set of elements
that is needed for the layout process. Each element is important in the
creation of areas.</p>
</section>
<section>
<title>Other Elements</title>
<p>
The remaining FO Objects are things like page-sequence,
title and color-profile. These are handled by their parent
element; i.e. the root looks after the declarations and the
declarations maintains a list of colour profiles. The
page-sequences are direct descendents of root.
</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/images.xml
Index: images.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>Images</title>
</header>
<body>
<section>
<title>Images in FOP</title>
<p>Images may only be needed to be loaded when the image is rendered to the
output or to find the dimensions.<br/>
An image url may be invalid, this can be costly to find out so we need to
keep a list of invalid image urls.</p>
<p>We have a number of different caching schemes that are possible.</p>
<p>All images are referred to using the url given in the XSL:FO after
removing "url('')" wrapping. This does
not include any sort of resolving such as relative -> absolute. The
external graphic in the FO Tree and the image area in the Area Tree only
have the url as a reference.
The images are handled through a static interface in ImageFactory.</p>
<section>
<title>Threading</title>
<p>In a single threaded case with one document the image should be released
as soon as the renderer caches it. If there are multiple documents then
the images could be held in a weak cache in case another document needs to
load the same image.</p>
<p>In a multi threaded case many threads could be attempting to get the same
image. We need to make sure an image will only be loaded once at a
particular time. Once a particular document is finished then we can move
all the images to a common weak cache.</p>
</section>
<section>
<title>Caches</title>
<section>
<title>LRU</title>
<p>All images are in a common cache regardless of context. To limit the size
of the cache the LRU image is removed to keep the amount of memory used
low. Each image can supply the amount of data held in memory.</p>
</section>
<section>
<title>Context</title>
<p>Images are cached according to the context, using the FOUserAgent as a key.
Once the context is finished the images are added to a common weak hashmap
so that other contexts can load these images or the data will be garbage
collected if required.</p>
<p>If images are to be used commonly then we cannot dispose of data in the
FopImage when cached by the renderer. Also if different contexts have
different base directories for resolving relative url's then the loading
and caching must be separate. We can have a cache that shares images among
all contexts or only loads an image for a context.</p>
</section>
<p>The cache uses an image loader so that it can synchronize the image
loading on an image by image basis. Finding and adding an image loader to
the cache is also synchronized to prevent thread problems.</p>
</section>
<section>
<title>Invalid Images</title>
<p>
If an image cannot be loaded for some reason, for example the url is
invalid or the image data is corrupt or an unknown type. Then it should
only attempt to load the image once. All other attempts to get the image
should return null so that it can be easily handled.<br/>
This will prevent any extra processing or waiting.</p>
</section>
<section>
<title>Reading</title>
<p>Once a stream is opened for the image url then a set of image readers is
used to determine what type of image it is. The reader can peek at the
image header or if necessary load the image. The reader can also get the
image size at this stage.
The reader then can provide the mime type to create the image object to
load the rest of the information.</p>
</section>
<section>
<title>Data</title>
<p>The data usually need for an image is the size and either a bitmap or the
original data. Images such as jpeg and eps can be embedded into the
document with the original data. SVG images are converted into a DOM which
needs to be rendered to the PDF. Other images such as gif, tiff etc. are
converted into a bitmap.
Data is loaded by the FopImage by calling load(type) where type is the type of data
to load.</p>
</section>
<section>
<title>Rendering</title>
<p>Different renderers need to have the information in different forms.</p>
<section>
<title>PDF</title>
<dl><dt>original data</dt> <dd>JPG, EPS</dd>
<dt>bitmap</dt> <dd>gif, tiff, bmp, png</dd>
<dt>other</dt> <dd>SVG</dd></dl>
</section>
<section>
<title>PS</title>
<dl><dt>bitmap</dt> <dd>JPG, gif, tiff, bmp, png</dd>
<dt>other</dt> <dd>SVG</dd></dl>
</section>
<section>
<title>awt</title>
<dl><dt>bitmap</dt> <dd>JPG, gif, tiff, bmp, png</dd>
<dt>other</dt> <dd>SVG</dd></dl>
</section>
<p>The renderer uses the url to retrieve the image from the ImageFactory and
then load the required data depending on the image mime type. If the
renderer can insert the image into the document and use that data for all
future references of the same image then it can cache the reference in the
renderer and the image can be released from the image cache.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/index.xml
Index: index.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>Understanding FOP Design</title>
<subtitle>Tutorial series about Design Approach to FOP</subtitle>
</header>
<body>
<section>
<title>Introduction</title>
<p>
Welcome to the understanding series. This will be
a series of notes for developers to understand how FOP
works. We will
attempt to clarify the processes involved to go from xml(fo)
to pdf or other formats. Some areas will get more
complicated as we proceed.
</p>
<section>
<title>Overview</title>
<p>FOP takes an xml file does its magic and then writes a document to a
stream.</p>
<p>xml -> [FOP] -> document</p>
<p>The document could be pdf, ps etc. or directed to a printer or the
screen. The principle remains the same. The xml document must be in the XSL:FO
format.</p>
<p>For convenience we provide a mechanism to handle XML+XSL as
input.</p>
<p>The xml document is always handled internally as SAX. The SAX events
are used to read the elements, attributes and text data of the FO document.
After the manipulation of the data the renderer writes out the pages in the
appropriate format. It may write as it goes, a page at a time or the whole
document at once. Once finished the document should contain all the data in
the
chosen format ready for whatever use.</p>
</section>
<section>
<title>Stages</title>
<p>The fo data goes through a few stages. Each piece
of data will generally go through the process in the same way but some
information may be used a number of times or in a different order. To reduce
memory one stage will start before the previous is completed.</p>
<p>SAX Handler -> FO Tree -> Layout Managers -> Area Tree
-> Render -> document</p>
<p>In the case of rtf, mif etc. <br/>SAX Handler -> FO Tree ->
Structure Renderer -> document</p>
<p>The FO Tree is constructed from the xml document. It is an internal
representation of the xml document and it is like a DOM with some differences.
The Layout Managers use the FO Tree do their layout stuff and create an Area
Tree. The Area Tree is a representation of the final result. It is a
representation of a set of pages containing the text and other graphics. The
Area Tree is then given to a Renderer. The Renderer can read the Area Tree and
convert the information into the render format. For example the PDF Renderer
creates a PDF Document. For each page in the Area Tree the renderer creates a
PDF Page and places the contents of the page into the PDF Page. Once a PDF
Page
is complete then it can be written to the output stream.</p>
<p>For the structure documents the Structure listener will read
directly from the FO Tree and create the document. These documents do not need
the layout process or the Area Tree.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/layout_managers.xml
Index: layout_managers.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>Layout Managers</title>
</header>
<body>
<section>
<title>Layout Managers</title>
<p>The role of the layout managers is to build the Area Tree by using the
information from the FO Tree. The layout managers decide where information
is placed in the area tree.</p>
<p>A layout manager is typically associated with an FO Object but not always.</p>
<p>The layout managers are in between the FO Tree and the Area Tree. They get
information from the FO Tree and create areas and build the pages. They
hold the state of the layout process as it builds up the areas and pages.
They also manage the handling of breaks and spacing between areas.</p>
<p>FO Objects can have two types of properties, ones that relate to the layout and
ones that relate to the rendering. THe layout related properties area used by the
layout managers to determine how and where to create the areas. The render related
properties should be passed through to the renderer in the most efficient way possible.
</p>
<section>
<title>Block Areas</title>
<p>When a block creating element is complete then it is possible to build the
block area and add it to the paprent.</p>
<p>A block area will contain either more block areas or line areas, which are
special block areas. The line areas are created by the LineLayoutManager
in which the inline areas flow into.</p>
<p>So a block area manager handles the lines or blocks as its children and
determines things like spacing and breaks.</p>
<p>In the case of tables and lists the blocks are stacked in a specific way
that needs to be handled by the layout manager.</p>
</section>
<section>
<title>Side Floats</title>
<p>Side floats alter the length of the inline progression dimension for the
current line and following lines for the size of the float.</p>
<p>This means that the float needs to be handled by the block layout manager
so that it can adjust the available inline progression dimension for the
relevant line areas.</p>
</section>
<section>
<title>Footnotes and Before Floats</title>
<p>Footnotes and Before Floats are placed in special areas in the body region
of the page. The size of these areas is determined by the content. This in
turn effects the available size of the main reference area that contains
the flow.</p>
<p>A layout manager handles the adding and removing of footnotes/floats, this in
turn effects the available space in the main reference area.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/pdf_library.xml
Index: pdf_library.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>PDF Library</title>
</header>
<body>
<section>
<title>PDF Library</title>
<p>The PDF Library is an independant package of classes in FOP. These class
provide a simple way to construct documents and add the contents. The
classes are found in <code>org.apache.fop.pdf.*</code>.</p>
<section>
<title>PDF Document</title>
<p>This is where most of the document is created and put together.</p>
<p>It sets up the header, trailer and resources. Each page is made and added to the
document.
There are a number of methods that can be used to create/add certain PDF objects to
the document.</p>
</section>
<section>
<title>Building PDF</title>
<p>The PDF Document is built by creating a page for each page in the Area Tree.</p>
<p> This page then has all the contents added.
The page is then added to the document and available objects can be written to the
output stream.</p>
<p>The contents of the page are things such as text, lines, images etc.
The PDFRenderer inserts the text directly into a pdf stream.
The text consists of markup to set fonts, set text position and add text.</p>
<p>Most of the simple pdf markup is inserted directly into a pdf stream.
Other more complex objects or commonly used objects are added through java classes.
Some pdf objects such as an image consists of two parts.</p>
<p>It has a separate object for the image data and another bit of markup to display
the image in a certain position on the page.
</p><p>The java objects that represent a pdf object implement a method that returns
the markup for inserting into a stream.
The method is: byte[] toPDF().</p>
</section>
<section>
<title>Features</title>
<section>
<title>Fonts</title>
<p>Support for embedding fonts and using the default Acrobat fonts.
</p></section>
<section>
<title>Images</title>
<p>Images can be inserted into a page. The image can either be inserted as a pixel
map or directly insert a jpeg image.
</p></section>
<section>
<title>Stream Filters</title>
<p>A number of filters are available to encode the pdf streams. These filters can
compress the data or change it such as converting to hex.
</p></section>
<section>
<title>Links</title>
<p>A pdf link can be added for an area on the page. This link can then point to an
external destination or a position on any page in the document.
</p></section>
<section>
<title>Patterns</title>
<p>The fill and stroke of graphical objects can be set with a colour, pattern or
gradient.
</p></section>
<p>The are a number of other features for handling pdf markup relevent to creating
PDF files for FOP.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/properties.xml
Index: properties.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>Properties</title>
</header>
<body>
<section>
<title>Property Handling</title>
<p>During XML Parsing, the FO tree is constructed. For each FO object (some
subclass of FObj), the tree builder then passes the list of all
attributes specified on the FO element to the handleAttrs method. This
method converts the attribute specifications into a PropertyList.</p>
<p>The actual work is done by a PropertyListBuilder (PLB for short). The
basic idea of the PLB is to handle each attribute in the list in turn,
find an appropriate "Maker" for it, call the Maker to convert the
attribute value into a Property object of the correct type, and store
that Property in the PropertyList.</p>
<section>
<title>Finding a Maker</title>
<p>
The PLB finds a "Maker" for the property based on the attribute name and
the element name. Most Makers are generic and handle the attribute on
any element, but it's possible to set up an element-specific property
Maker. The attribute name to Maker mappings are automatically created
during the code generation phase by processing the XML property
description files.</p>
</section>
<section>
<title>Processing the attribute list</title>
<p>The PLB first looks to see if the font-size property is specified, since
it sets up relative units which can be used in other property
specifications. Each attribute is then handled in turn. If the attribute
specifies part of a compound property such as space-before.optimum, the
PLB looks to see if the attribute list also contains the "base" property
(space-before in this case) and processes that first.</p>
</section>
<section>
<title>How the Property Maker works</title>
<p>There is a family of Maker objects for each of the property datatypes,
such as Length, Number, Enumerated, Space, etc. But since each Property
has specific aspects such as whether it's inherited, its default value,
its corresponding properties, etc. there is usually a specific Maker for
each Property. All these Maker classes are created during the code
generation phase by processing (using XSLT) the XML property description
files to create Java classes.</p>
<p>The Maker first checks for "keyword" values for a property. These are
things like "thin, medium, thick" for the border-width property. The
datatype is really a Length but it can be specified using these keywords
whose actual value is determined by the "User Agent" rather than being
specified in the XSL standard. For FOP, these values are currently
defined in foproperties.xml. The keyword value is just a string, so it
still needs to be parsed as described next.</p>
<p>The Maker also checks to see if the property is an Enumerated type and
then checks whether the value matches one of the specified enumeration
values.</p>
<p>Otherwise the Maker uses the property parser in the fo.expr package to
evaluate the attribute value and return a Property object. The parser
interprets the expression language and performs numeric operations and
function call evaluations.</p>
<p>If the returned Property value is of the correct type (specificed in
foproperties.xml, where else?), the Maker returns it. Otherwise, it may
be able to convert the returned type into the correct type.</p>
<p>Some kinds of property values can't be fully resolved during FO tree
building because they depend on layout information. This is the case of
length values specified as percentages and of the special
proportional-column-width(x) specification for table-column widths.
These are stored as special kinds of Length objects which are evaluated
during layout. Expressions involving "em" units which are relative to
font-size _are_ resolved during the FO tree building however.</p>
</section>
<section>
<title>Structure of the PropertyList</title>
<p>The PropertyList extends HashMap and its basic function is to associate
Property value objects with Property names. The Property objects are all
subclasses of the base Property class. Each one simply contains a
reference to one of the property datatype objects. Property provides
accessors for all known datatypes and various subclasses override the
accessor(s) which are reasonable for the datatype they store.</p>
<p>The PropertyList itself provides various ways of looking up Property
values to handle such issues as inheritance and corresponding
properties. </p>
<p>The main logic is:<br/>If the property is a writing-mode relative property (using
start, end,
before or after in its name), the corresponding absolute property value
is returned if it's explicitly set on this FO. <br/>Otherwise, the
writing-mode relative value is returned if it's explicitly set. If the
property is inherited, the process repeats using the PropertyList of the
FO's parent object. (This is easy because each PropertyList points to
the PropertyList of the nearest ancestor FO.) If the property isn't
inherited or no value is found at any level, the initial value is
returned.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/renderers.xml
Index: renderers.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>Renderers</title>
</header>
<body>
<section>
<title>Renderers</title>
<section>
<title>Renderers</title>
<p>A renderer is used to convert the Area Tree into the output document.
The renderer is given the tree one page at a time. All pages are supplied
in the order they appear in the document. In order to save memory it is
possble to render the pages out of order. Any page that is not reeady to
be rendered is setup by the renderer first so that it can reserve a space
or reference for when the page is ready to be rendered.</p>
<p>The AbstractRenderer does most of the work to iterate through the area
tree parts. This means that the most renderers simply need to implement
the specific parts with inserting text, images and lines. The methods can
easily be overridden to handle things in a different way or do some extra
processing.</p>
</section>
<section>
<title>Fonts</title>
<p>The fonts are setup by the renderer being used. The font metrics are used
during the layout process to determine the size of characters.</p>
</section>
<section>
<title>Render Context</title>
<p>The render context is used by handlers. It contains information about the
current state of the renderer. Such as the page, the position and any
other miscellanous objects that are required to draw into the page.</p>
</section>
<section>
<title>XML Handling</title>
<p>A document may contain information in the form of XML for an image or
instream foreign object. This XML is handled
through the user agent. A standard extension for PDF is the SVG handler.</p><p>
If there is XML in the SVG namespace it is given to the handler which
renders the SVG into the pdf document at the given location.
This separation means that other XML handlers can easily be added.</p>
</section>
<section>
<title>Extensions</title>
<p>Document level extensions are handled with an extension handler. This
handles the information from the AreaTree and adds renders it to the
document. An example is the pdf bookmarks. This information first needs to
have all references resolved. Then the extension handler is ready to put
the information into the pdf document.</p>
</section>
<section>
<title>Types</title>
<section>
<title>PDF</title>
<p>This uses the PDFDocument classes to create a PDF document. This supports
out of order rendering as it is possible to reserve a pdf page object that
can be later filled. Most of the work is to insert text or create lines.
SVG is handled by the XML handler that uses the PDFGraphics2D and batik to
draw the svg into the pdf page.</p><p>
This also allows for font embedding.</p>
</section>
<section>
<title>SVG</title>
<p>This creates a single svg document that contains all the pages rendered
with page sequences horizontally and pages vertically. This also adds
links between the pages so that it can be viewed by clicking on the page
to go to the next page.</p>
</section>
<section>
<title>TXT</title>
<p>This simply outputs to a text document.</p></section>
<section>
<title>AWT</title>
<p>This draws the pages into an AWT graphic.</p></section>
<section>
<title>PS and PCL</title>
<p>Similar to PDF.</p></section>
<section>
<title>XML</title>
<p>Creates an XML file that represents the AreaTree.</p>
</section>
<section>
<title>Print</title>
<p>This prints the document using the java printing facitlities. The AWT
rendering is used to draw the pages onto the printjob.
</p>
</section>
<section>
<title>RTF and MIF</title>
<p>These formats do not use this rendering mechanism.</p>
</section>
</section>
<section>
<title>Adding a Renderer</title>
<p>It is also possible to add other renderers. The renderer simply needs to
implement the Renderer interface. The AbstractRenderer does most of what
is needed so it is better to extend this. This means that you only need to
implement the basic functionality such as text and lines.
</p>
</section>
<section>
<title>Multiple Renderers</title>
<p>The layout of the document depends mainly on the font being used.
If two renderers have the same font metrics then it is possible to render
the Area Tree in each renderer. This can be handled by the AreaTree
Handler.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/svg.xml
Index: svg.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>SVG</title>
</header>
<body>
<section>
<title>SVG</title>
<p>SVG is rendered through Batik.</p><p>The XML from the XSL:FO document
is converted into an SVG DOM with batik. This DOM is then set as the Document
on the Foreign Object area in the Area Tree.</p><p>This DOM is then available
to
be rendered by the renderer.</p><p>SVG is rendered in the renderers via an
XMLHandler in the FOUserAgent. This XML handler is used to render the SVG. The
SVG is rendered by using batik. Batik converts the SVG DOM into an internal
structure that can be drawn into a Graphics2D. So for PDF we use a
PDFGraphics2D to draw into.</p><p>This creates the necessary PDF information to
create the SVG image in the PDF document.</p><p>Most of the work is done in the
PDFGraphics2D class. There are also a few bridges that are plugged into batik
to provide different behaviour for some SVG elements.</p>
<section>
<title>Text Drawing</title>
<p>Normally batik converts text into a set of curved
shapes. </p><p>This is handled as any other shapes when rendering to the
output. This
is not always desirable as the shapes have very fine curves. This can cause
the
output to look a bit bad in PDF and PS (it can be drawn properly but is not by
default). These curves also require much more data than the original
text.</p><p>To handle this there is a PDFTextElementBridge that is set when
using the bridge in batik. If the text is simple enough for the text to be
drawn in the PDF as with all other text then this sets the TextPainter to use
the PDFTextPainter. This inserts the text directly into the PDF using the
drawString method on the PDFGraphics2D.</p><p>Text is considered simple if the
font is available, the font size is useable and there are no tspans or other
complications. This can make the resulting PDF significantly
smaller.</p>
</section>
<section>
<title>PDF Links</title>
<p>To support links in PDF another batik
element bridge is used. The PDFAElementBridge creates a PDFANode which inserts
a link into the PDF document via the PDFGraphics2D.</p><p>Since links are
positioned on the page without any transforms then we need to transform the
coordinates of the link area so that they match the current position of the a
element area. This transform may also need to account for the svg being
positioned on the page.</p>
</section>
<section>
<title>Images</title>
<p>Images are normally drawn
into the PDFGraphics2D. This then creates a bitmap of the image data that can
be inserted into the PDF document. </p><p>As PDF can support jpeg images then
another
element bridge is used so that the jpeg can be directly inserted into the
PDF.</p>
</section>
<section>
<title>PDF Transcoder</title>
<p>Batik provides a mechanism to
convert SVG into various formats. Through FOP we can convert an SVG document
into a single paged PDF document. The page contains the SVG drawn as best as
possible on the page. There is a PDFDocumentGraphics2D that creates a
standalone PDF document with a single page. This is then drawn into by batik
in
the same way as with the PDFGraphics2D.</p>
</section>
<section>
<title>Other Outputs</title>
<p>When rendering to AWT the SVG is simply drawn onto the
awt canvas using batik.</p><p>The PS Renderer uses a similar technique as the
PDF Renderer.</p><p>The SVG Renderer simply embeds the SVG inside an svg
element.</p>
</section>
</section>
</body>
</document>
1.1
xml-fop/src/documentation/content/xdocs/design/understanding/xml_parsing.xml
Index: xml_parsing.xml
===================================================================
<?xml version="1.0" standalone="no"?>
<!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";>
<document>
<header>
<title>XML Parsing</title>
</header>
<body>
<section>
<title>XML Parsing</title>
<p>Since everyone knows the basics we can get
into the various stages starting with the XML handling.</p>
<section>
<title>XML Input</title>
<p>FOP can take the input XML in a number of ways:
</p>
<ul>
<li>SAX Events through SAX Handler
<ul>
<li>
<code>FOTreeBuilder</code> is the SAX Handler which is
obtained through <code>getContentHandler</code> on
<code>Driver</code>.
</li>
</ul>
</li>
<li>
DOM which is converted into SAX Events
<ul>
<li>
The conversion of a DOM tree is done via the
<code>render(Document)</code> method on
<code>Driver</code>.
</li>
</ul>
</li>
<li>
data source which is parsed and converted into SAX Events
<ul>
<li>
The <code>Driver</code> can take an
<code>InputSource</code> as input. This can use a
<code>Stream</code>, <code>String</code> etc.
</li>
</ul>
</li>
<li>
XML+XSLT which is transformed using an XSLT Processor and
the result is fired as SAX Events
<ul>
<li>
<code>XSLTInputHandler</code> is used as an
<code>InputSource</code> in the
render(<code>XMLReader</code>,
<code>InputSource</code>) method on
<code>Driver</code>
</li>
</ul>
</li>
</ul>
<p>The SAX Events which are fired on the SAX Handler, class
<code>FOTreeBuilder</code>, must represent an XSL:FO
document. If not there will be an
error. Any problems with the XML being well formed are
handled here.</p>
</section>
<section>
<title>Element Mappings</title>
<p> The element mapping is a hashmap of all
the elements in a particular namespace. This makes it easy
to create a
different object for each element. Element mappings are
static to save on
memory. </p><p>To add an extension a developer can put in
the classpath a jar
that contains the file
<code>/META-INF/services/org.apache.fop.fo.ElementMapping</code>.
This must contain a line with the fully qualified name of a
class that
implements the <em>org.apache.fop.fo.ElementMapping</em>
interface. This will then be
loaded automatically at the start. Internal mappings are:
FO, SVG and Extension
(pdf bookmarks)</p></section>
<section>
<title>Tree Building</title>
<p>The SAX Events will fire all the information
for the document with start element, end element, text data
etc. This
information is used to build up a representation of the FO
document. To do this
for a namespace there is a set of element mappings. When an
element + namepsace
mapping is found then it can create an object for that
element. If the element
is not found then it creates a dummy object or a generic
DOM for unknown
namespaces.</p>
<p>The object is then setup and then given attributes for the
element.
For the FO Tree the attributes are converted into
properties. The FO objects
use a property list mapping to convert the attributes into
a list of properties
for the element. For other XML, for example SVG, a DOM of
the XML is
constructed. This DOM can then be passed through to the
renderer. Other element
mappings can be used in different ways, for example to
create elements that
create areas during the layout process or setup information
for the renderer
etc.</p>
<p>
While the tree building is mainly about creating the FO Tree
there are some stages that can propagate to the renderer. At
the end of a page sequence we know that all pages in the
page sequence can be laid out without being effected by any
further XML. The significance of this is that the FO Tree
for the page sequence may be able to be disposed of. The
end of the XML document also tells us that we can finalise
the output document. (The layout of individual pages is
accomplished by the layout managers page at a time;
i.e. they do not need to wait for the end of the page
sequence. The page may not yet be complete, however,
containing forward page number references, for example.)
</p>
</section>
</section>
</body>
</document>
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