From 01e2426b496f0eff10dbb9582f99b0cc7ca74bdf Mon Sep 17 00:00:00 2001
From: James Bursa <james@netsurf-browser.org>
Date: Tue, 7 Oct 2003 21:41:55 +0000
Subject: [project @ 2003-10-07 21:41:55 by bursa] Implementing a new CSS
 property overview.

svn path=/import/netsurf/; revision=349
---
 Docs/developer | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

(limited to 'Docs/developer')

diff --git a/Docs/developer b/Docs/developer
index 8acaca65a..83cd61812 100644
--- a/Docs/developer
+++ b/Docs/developer
@@ -97,4 +97,74 @@ http://netsurf.strcprstskrzkrk.co.uk/developer/
 - libpng (PNG support)			http://www.libpng.org/pub/png/libpng.html
 - zlib					http://www.gzip.org/zlib/
 
+\section addcss Implementing a new CSS property
+
+In this section I go through adding a CSS property to NetSurf, using the
+'white-space' property as an example. -- James Bursa
+
+1. Read and understand the description of the property in the CSS specification
+   (I have worked from CSS 2, but now 2.1 is probably better).
+
+These changes are required in the css directory:
+
+2. Add the property to css_enums. This file is used to generate css_enum.h
+   and css_enum.c:
+   \code css_white_space inherit normal nowrap pre \endcode
+   (I'm not doing pre-wrap and pre-line for now.)
+
+3. Add fields to struct ::css_style to represent the property:
+   \code css_white_space white_space; \endcode
+
+4. Add a parser function for the property to ruleset.c. Declare a new
+   function:
+   \code static void parse_white_space(struct css_style * const s, const struct css_node * const v); \endcode
+   and add it to ::property_table:
+   \code { "white-space",      parse_white_space }, \endcode
+   This will cause the function to be called when the parser comes to a rule
+   giving a value for white-space. The function is passed a linked list of
+   struct ::css_node, each of which corresponds to a token in the CSS source,
+   and must update s to correspond to that rule. For white-space, the
+   implementation is simply:
+\code
+void parse_white_space(struct css_style * const s, const struct css_node * const v)
+{
+	css_white_space z;
+	if (v->type != CSS_NODE_IDENT || v->next != 0)
+		return;
+	z = css_white_space_parse(v->data);
+	if (z != CSS_WHITE_SPACE_UNKNOWN)
+		s->white_space = z;
+}
+\endcode
+   First we check that the value consists of exactly one identifier, as
+   described in the specification. If it is not, we ignore it, since it may be
+   some future CSS. The css_white_space_parse() function is generated in
+   css_enum.c, and converts a string giving a value to a constant. If the
+   conversion succeeds, the style s is updated.
+
+5. Add defaults for the style to ::css_base_style, ::css_empty_style, and
+   ::css_blank_style in css.c. The value in css_base_style should be the one
+   given as 'Initial' in the spec, and the value in css_empty_style should be
+   inherit. If 'Inherited' is yes in the spec, the value in css_blank_style
+   should be inherit, otherwise it should be the one given as 'Initial'. Thus
+   for white-space, which has "Initial: normal, Inherited: yes" in the spec, we
+   use CSS_WHITE_SPACE_NORMAL in css_base_style and CSS_WHITE_SPACE_INHERIT in
+   the other two.
+
+6. Edit css_cascade() and css_merge() in css.c to handle the property. In
+   both cases for white-space this looks like:
+   \code
+	if (apply->white_space != CSS_WHITE_SPACE_INHERIT)
+		style->white_space = apply->white_space;
+   \endcode
+   Add the property to css_dump_style() (not essential).
+
+Now the box, layout and / or redraw code needs to be changed to use the new
+style property. This varies much more depending on the property.
+
+For white-space, convert_xml_to_box() was changed to split text at newlines if
+white-space was pre, and to replace spaces with hard spaces for nowrap.
+Additionally, calculate_inline_container_widths() was changed to give the
+appropriate minimum width for pre and nowrap.
+
 */
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