Renderers


	Renderers


	Renderers

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.

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.


	Fonts

The fonts are setup by the renderer being used. The font metrics are used during the layout process to determine the size of characters.


	Render Context

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.


	XML Handling

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.

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.


	Extensions

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.


	Types


	PDF

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.

This also allows for font embedding.


	SVG

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.


	TXT

This simply outputs to a text document.


	AWT

This draws the pages into an AWT graphic.


	PS and PCL

Similar to PDF.


	XML

Creates an XML file that represents the AreaTree.


	Print

This prints the document using the java printing facitlities. The AWT rendering is used to draw the pages onto the printjob.


	RTF and MIF

These formats do not use this rendering mechanism.


	Adding a Renderer

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.


	Multiple Renderers

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.


	Associated Tasks

Sort out multiple renderers concept.