netsurf/developer

Documentation for Developers

This document contains an overview of the code for NetSurf, and any other
information useful to developers.

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Source Code Overview

The source is split at top level as follows:

content -- fetching, caching, and converting content
desktop -- non-platform specific front-end
render -- HTML and CSS processing and layout
riscos -- RISC OS specific code
utils -- misc. useful functions

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content -- fetching, caching, and converting content

Each URL is stored in a struct content. This structure contains a union with
fields for each type of data (HTML, CSS, images).

The content_* functions provide a general interface for handling these
structures. A content of a specified type is created using content_create(),
data is fed to it using content_process_data(), terminated by a call to
content_convert(), which converts the content into a structure which can be
displayed easily.

The cache stores this converted content. When content is retrieved from the
cache, content_revive() should result in content which can be displayed (eg. by
loading any images and styles required and updating pointers to them).

Code should not usually use the fetch_* and cache_* functions directly, except
for cache_free(). Instead use fetchcache(), which checks the cache for a url and
fetches, converts, and caches it if not present.

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render -- HTML and CSS processing and layout

This is the process to render an HTML document:

First the HTML is parsed to a tree of xmlNodes using the HTML parser in libxml.
This happens simultaneously with the fetch [html_process_data()].

Any stylesheets which the document depends on are fetched and parsed.

The tree is converted to a 'box tree' by xml_to_box(). The box tree contains a
node for each block, inline element, table, etc. The aim of this stage is to
determine the 'display' or 'float' CSS property of each element, and create the
corresponding node in the box tree. At this stage the style for each element is
also calculated (from CSS rules and element attributes). The tree is normalised
so that each node only has children of permitted types (eg. TABLE_CELLs must be
within TABLE_ROWs) by adding missing boxes.

The box tree is passed to the layout engine [layout_document()], which finds the
space required by each element and assigns coordinates to the boxes, based on
the style of each element and the available width. This includes formatting
inline elements into lines, laying out tables, and positioning floats. The
layout engine can be invoked again on a already laid out box tree to reformat it
to a new width. Coordinates in the box tree are relative to the position of the
parent node.

The box tree can then be rendered using each node's coordinates.

box.[ch] -- definition of the box tree, conversion from xml tree, normalising
css* -- CSS parser and handler
html.[ch] -- interface to HTML processing
layout.[ch] -- layout engine

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Specifications

HTML 4.01	http://www.w3.org/TR/html401/
XHTML 1.0	http://www.w3.org/TR/xhtml1/
CSS2		http://www.w3.org/TR/REC-CSS2/
HTTP/1.1	http://www.w3.org/Protocols/rfc2616/rfc2616.html
PNG		http://www.w3.org/Graphics/PNG/

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Libraries

libxml (XML and HTML parser)		http://xmlsoft.org/
libcurl (HTTP, FTP, etc)		http://curl.haxx.se/libcurl/
OSLib (C interface to RISC OS SWIs)	http://ro-oslib.sourceforge.net/

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