path: root/Docs/developer
diff options
authorJames Bursa <>2003-10-07 21:41:55 +0000
committerJames Bursa <>2003-10-07 21:41:55 +0000
commit01e2426b496f0eff10dbb9582f99b0cc7ca74bdf (patch)
tree1196d80f81d4e56c4c1b36e30ef8ea0a9556e8c8 /Docs/developer
parentbbcdf13fe04bc56a3671db581df40307e65b81da (diff)
[project @ 2003-10-07 21:41:55 by bursa]
Implementing a new CSS property overview. svn path=/import/netsurf/; revision=349
Diffstat (limited to 'Docs/developer')
1 files changed, 70 insertions, 0 deletions
diff --git a/Docs/developer b/Docs/developer
index 8acaca65a..83cd61812 100644
--- a/Docs/developer
+++ b/Docs/developer
@@ -97,4 +97,74 @@
- libpng (PNG support)
- 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:
+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);
+ s->white_space = z;
+ 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
+ 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.