path: root/Docs/03-css
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authorJames Bursa <>2006-10-02 21:58:33 +0000
committerJames Bursa <>2006-10-02 21:58:33 +0000
commitc88b268f846e5501e19b5d75b0e8ac9b11858857 (patch)
treee09f15adccc34647b590638c1416c1df4ca027ca /Docs/03-css
parent118f435133cb5aa3a81fa84e29f69e563e2a0e35 (diff)
Split documentation into files by topic and convert to AsciiDoc format.
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+CSS parser
+CSS is tokenised by a re2c-generated scanner (scanner.l), and then parsed into a
+memory representation by a lemon-generated parser (parser.y, ruleset.c).
+Styles are retrieved using css_get_style(). They can be cascaded by
+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
+First 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).
+Add the property to css_enums. This file is used to generate css_enum.h and
+ css_white_space inherit normal nowrap pre
+(I'm not doing pre-wrap and pre-line for now.)
+Add fields to struct css_style to represent the property:
+ css_white_space white_space;
+Add a parser function for the property to ruleset.c. Declare a new function:
+ static void parse_white_space(struct css_style * const s, const struct css_node * const v);
+and add it to property_table:
+ { "white-space", parse_white_space },
+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
+ 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, v->data_length);
+ 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.
+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.
+Edit css_cascade() and css_merge() in css.c to handle the property. In both
+cases for white-space this looks like:
+ if (apply->white_space != CSS_WHITE_SPACE_INHERIT)
+ style->white_space = apply->white_space;
+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.