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Refactor the cascade

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Converting the specified value of some properties into a computed value
depends on the value of other properties. For example, the `em` unit
of any length depends on the `font-size` property.

Previously, we would do a first pass over applicable declarations
to build up a `values::computed::Context` struct with a number of fields
for each such piece of data from other properties.

This simplies the struct by instead having it contain the
set of computed values (for a given element) that is being populated
and classify properties into "early" and "other",
such that the only dependencies can be from "other" to "early".
We iterate applicable_declarations twice, first cascading "early" properties
then "other".
Unfortunately, it’s not easy to check that this classification is correct.
This commit is contained in:
Simon Sapin 2016-03-09 00:33:01 +01:00
parent bab28e5070
commit 529164e4a5
3 changed files with 213 additions and 339 deletions
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19
components/style/viewport.rs
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@ -8,7 +8,7 @@ use cssparser::{AtRuleParser, DeclarationListParser, DeclarationParser, Parser,
use euclid::scale_factor::ScaleFactor;
use euclid::size::{Size2D, TypedSize2D};
use parser::{ParserContext, log_css_error};
use properties::longhands;
use properties::INITIAL_VALUES;
use std::ascii::AsciiExt;
use std::collections::hash_map::{Entry, HashMap};
use std::fmt;
@ -594,21 +594,8 @@ impl MaybeNew for ViewportConstraints {
let context = Context {
is_root_element: false,
viewport_size: initial_viewport,
inherited_font_weight: longhands::font_weight::get_initial_value(),
inherited_font_size: longhands::font_size::get_initial_value(),
inherited_text_decorations_in_effect: longhands::_servo_text_decorations_in_effect::get_initial_value(),
font_size: longhands::font_size::get_initial_value(),
root_font_size: longhands::font_size::get_initial_value(),
display: longhands::display::get_initial_value(),
color: longhands::color::get_initial_value(),
text_decoration: longhands::text_decoration::get_initial_value(),
positioned: false,
floated: false,
border_top_present: false,
border_right_present: false,
border_bottom_present: false,
border_left_present: false,
outline_style_present: false,
inherited_style: &*INITIAL_VALUES,
style: INITIAL_VALUES.clone(),
};
// DEVICE-ADAPT § 9.3 Resolving 'extend-to-zoom'