Understanding FOP Design


	Understanding

The content of this Understanding series was all taken from the interactive fop development mailing list discussion .
We strongly advise you to join this mailing list and ask question about this series there.
idea of the issues being discussed.


	Introduction

Welcome to the understanding series. This will be a series of notes for developers to understand how FOP works. We will to pdf or other formats. Some areas will get more complicated as we proceed.


	Overview

stream.

The document could be pdf, ps etc. or directed to a printer or the format.

For convenience we provide a mechanism to handle XML+XSL as input.

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.


	Stages

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.

SAX Handler -> FO Tree -> Layout Managers -> Area Tree -> Render -> document

In the case of rtf, mif etc.
SAX Handler -> FO Tree -> Structure Renderer -> document

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.

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.


	Associated Tasks

Verify Structure Listener concept.


	Further Topics

XML parsing

FO Tree

Properties

Layout Managers

Layout Process

Handling Attributes

Area Tree

Renderers

Images

PDF Library

SVG