FO Tree

- Introduction -

-The FO Tree is an internal representation of the input XSL-FO document. +

+ FO Tree + Design of FO Tree Structure + + + +

+ +

+ Introduction +

The FO Tree is an internal representation of the input XSL-FO document. The tree is created by building the elements and attributes from the SAX events. The process of building the FO Tree corresponds to the Objectify step from the spec. -The Refinement step is part of reading and using the properties which may happen immediately or during the layout process. - -

-The FO Tree is used as an intermediatory structure which is converted +The Refinement step is part of reading and using the properties which may happen immediately or during the layout process.

The FO Tree is used as an intermediatory structure which is converted into the area tree. The complete FO tree should not be held in memory -since FOP should be able to handle FO documents of any size. -

- 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. -

- -

- FONode -

The base class for all objects in the tree is FONode. The base class for +since FOP should be able to handle FO documents of any size.

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.

+ FONode +

The base class for all objects in the tree is FONode. The base class for all FO Objects is FObj.

- -

-The class inheritance described above only describes the nature of the +

The class inheritance described above only describes the nature of the content. Every FO in FOP also has a parent, and a Vector of children. The parent attribute (in the Java sense), in particular, is used to enforce -constraints required by the FO hierarchy. -

- -

-FONode, among other things, ensures that FO's have a parent and that they -may have children. -

Each xml element is represented by a java object. For pagination the +constraints required by the FO hierarchy.

FONode, among other things, ensures that FO's have a parent and that they +may have children.

Each xml element is represented by a java object. For pagination the classes are in org.apache.fop.fo.pagination.*, for elements in the flow they are in org.apache.fop.fo.flow.* and some others are in org.apache.fop.fo.*.

- -

- Making FO's -

There is a class for each element in the FO set. An object is created for +

+ Making FO's +

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.

Some validity checking is done during these steps. The user can be warned of the error and processing can continue if possible. -

- 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 - handleAttributes() and - setuserAgent(), common to FONode, - are used in this process. The object will then be given any - text data or child elements. Then the end() - 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. -

- -

-An FO maker is read from a hashmap lookup using the namespace and +

Some validity checking is done during these steps. The user can be warned of the error and processing can continue if possible.

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 handleAttributes() and setuserAgent(), common to FONode, are used in this process. +The object will then be given any text data or child elements. +Then the end() 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.

An FO maker is read from a hashmap lookup using the namespace and element name. This maker is then used to create a new class that represents an FO element. This is then added to the FO tree as a child -of the current parent. -

- -

- Properties - -

The XML attributes on each element are passed to the object. The objects -that represent FO objects then convert the attributes into properties. -

- -

Since properties can be inherited the PropertyList class handles resolving +of the current parent.

+ Properties +

The XML attributes on each element are passed to the object. The objects +that represent FO objects then convert the attributes into properties.

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. -

- -

In some cases the element may be moved to have a different parent, for +automatically during the build process.

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.

- -

-Properties (recall that FO's have properties, areas have traits, and XML +

Properties (recall that FO's have properties, areas have traits, and XML nodes have attributes) are also a concern of FOTreeBuilder. It accomplishes this by using a PropertyListBuilder. There is a separate PropertyListBuilder for each namespace encountered @@ -112,101 +75,73 @@ contain element-specific property maker hashes; these are based on the local name of the flow object, ie. table-row, not fo:table-row. If an element-specific property mapping exists, it is preferred to the generic mapping.

The base class for all +

The base class for all properties is Property, and all the property makers extend Property.Maker. A more complete discussion of the property -architecture may be found in Properties. -

- -

- Foreign XML -

-FOP supports the handlingof foreign XML. +architecture may be found in Properties.

+ Foreign XML +

FOP supports the handlingof foreign XML. The XML is converted internally into a DOM, this is then available to the FO tree to convert the DOM into another format which can be rendered. In the case of SVG the DOM needs to be created with Batik, so an element mapping is used to read all elements in the SVG namespace and pass them -into the Batik DOM. -

- -

- Extensions -

-It is possible to add extensions to FOP so that you can extend the ability of +into the Batik DOM.

+ Extensions +

It is possible to add extensions to FOP so that you can extend the ability of FOP with respect to render output, document specific information or extended -layout functionality. -

- -

- Foreign XML - -

The base class for foreign XML is XMLObj. This class handles creating a +layout functionality.

+ Foreign XML +

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.

- -

If some special processing is needed then the top level element can extend +

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. -

- -

Foreign XML will usually be in an fo:instream-foreign-object, the XML will +batik and gets the size of the svg.

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. -

- -

By using element mappings it is possible to read other XML and either

set information on the area tree
create pseudo FO Objects that create areas in the area tree
create FO Objects

- -

- Unknown Elements -

If an element is in a known namespace but the element is unknown then an +it. Other XML from an unknwon namespace will be ignored.

By using element mappings it is possible to read other XML and either

set information on the area tree
create pseudo FO Objects that create areas in the area tree
create FO Objects

+ Unknown Elements +

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.

- -

- Page Masters -

- 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. -

- -

- Flow -

The elements that are in the flow of the document are a set of elements +

+ Page Masters +

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.

+ Flow +

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.

- -

- Other Elements - -

- 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. -

- - +