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style: Document the restyle hints code, and make it operate on TElement.

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This removes the annoying constraint of having to provide the current state from
outside of the restyle hints code.
This commit is contained in:
Emilio Cobos Álvarez 2017-01-01 23:53:34 +01:00
parent c5f2142d8f
commit fa8874fb14
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4 changed files with 101 additions and 53 deletions
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4
components/style/data.rs
View file

@ -295,10 +295,8 @@ impl RestyleData {
}
// Compute the hint.
let state = element.get_state();
let mut hint = stylist.compute_restyle_hint(&element,
self.snapshot.as_ref().unwrap(),
state);
self.snapshot.as_ref().unwrap());
// If the hint includes a directive for later siblings, strip it out and
// notify the caller to modify the base hint for future siblings.

46
components/style/restyle_hints.rs
View file

@ -4,13 +4,16 @@
//! Restyle hints: an optimization to avoid unnecessarily matching selectors.
#![deny(missing_docs)]
use Atom;
use dom::TElement;
use element_state::*;
#[cfg(feature = "gecko")]
use gecko_bindings::structs::nsRestyleHint;
#[cfg(feature = "servo")]
use heapsize::HeapSizeOf;
use selector_parser::{AttrValue, ElementExt, NonTSPseudoClass, Snapshot, SelectorImpl};
use selector_parser::{AttrValue, NonTSPseudoClass, Snapshot, SelectorImpl};
use selectors::{Element, MatchAttr};
use selectors::matching::{MatchingReason, StyleRelations};
use selectors::matching::matches_complex_selector;
@ -18,13 +21,14 @@ use selectors::parser::{AttrSelector, Combinator, ComplexSelector, SimpleSelecto
use std::clone::Clone;
use std::sync::Arc;
/// When the ElementState of an element (like IN_HOVER_STATE) changes, certain
/// pseudo-classes (like :hover) may require us to restyle that element, its
/// siblings, and/or its descendants. Similarly, when various attributes of an
/// element change, we may also need to restyle things with id, class, and
/// attribute selectors. Doing this conservatively is expensive, and so we use
/// RestyleHints to short-circuit work we know is unnecessary.
bitflags! {
/// When the ElementState of an element (like IN_HOVER_STATE) changes,
/// certain pseudo-classes (like :hover) may require us to restyle that
/// element, its siblings, and/or its descendants. Similarly, when various
/// attributes of an element change, we may also need to restyle things with
/// id, class, and attribute selectors. Doing this conservatively is
/// expensive, and so we use RestyleHints to short-circuit work we know is
/// unnecessary.
pub flags RestyleHint: u32 {
#[doc = "Rerun selector matching on the element."]
const RESTYLE_SELF = 0x01,
@ -99,26 +103,28 @@ pub trait ElementSnapshot : Sized + MatchAttr<Impl=SelectorImpl> {
}
struct ElementWrapper<'a, E>
where E: ElementExt
where E: TElement,
{
element: E,
snapshot: Option<&'a Snapshot>,
}
impl<'a, E> ElementWrapper<'a, E>
where E: ElementExt
where E: TElement,
{
/// Trivially constructs an `ElementWrapper` without a snapshot.
pub fn new(el: E) -> ElementWrapper<'a, E> {
ElementWrapper { element: el, snapshot: None }
}
/// Trivially constructs an `ElementWrapper` with a snapshot.
pub fn new_with_snapshot(el: E, snapshot: &'a Snapshot) -> ElementWrapper<'a, E> {
ElementWrapper { element: el, snapshot: Some(snapshot) }
}
}
impl<'a, E> MatchAttr for ElementWrapper<'a, E>
where E: ElementExt,
where E: TElement,
{
type Impl = SelectorImpl;
@ -202,7 +208,7 @@ impl<'a, E> MatchAttr for ElementWrapper<'a, E>
}
impl<'a, E> Element for ElementWrapper<'a, E>
where E: ElementExt<Impl=SelectorImpl>
where E: TElement,
{
fn match_non_ts_pseudo_class(&self, pseudo_class: NonTSPseudoClass) -> bool {
let flag = SelectorImpl::pseudo_class_state_flag(&pseudo_class);
@ -393,6 +399,7 @@ impl DependencySet {
}
}
/// Create an empty `DependencySet`.
pub fn new() -> Self {
DependencySet {
state_deps: vec![],
@ -401,10 +408,13 @@ impl DependencySet {
}
}
/// Return the total number of dependencies that this set contains.
pub fn len(&self) -> usize {
self.common_deps.len() + self.attr_deps.len() + self.state_deps.len()
}
/// Create the needed dependencies that a given selector creates, and add
/// them to the set.
pub fn note_selector(&mut self, selector: &Arc<ComplexSelector<SelectorImpl>>) {
let mut cur = selector;
let mut combinator: Option<Combinator> = None;
@ -434,18 +444,22 @@ impl DependencySet {
}
}
/// Clear this dependency set.
pub fn clear(&mut self) {
self.common_deps.clear();
self.attr_deps.clear();
self.state_deps.clear();
}
pub fn compute_hint<E>(&self, el: &E,
snapshot: &Snapshot,
current_state: ElementState)
/// Compute a restyle hint given an element and a snapshot, per the rules
/// explained in the rest of the documentation.
pub fn compute_hint<E>(&self,
el: &E,
snapshot: &Snapshot)
-> RestyleHint
where E: ElementExt + Clone
where E: TElement + Clone,
{
let current_state = el.get_state();
let state_changes = snapshot.state()
.map_or_else(ElementState::empty, |old_state| current_state ^ old_state);
let attrs_changed = snapshot.has_attrs();
@ -483,7 +497,7 @@ impl DependencySet {
state_changes: &ElementState,
attrs_changed: bool,
hint: &mut RestyleHint)
where E: ElementExt
where E: TElement,
{
if hint.is_all() {
return;

90
components/style/selector_parser.rs
View file

@ -4,6 +4,8 @@
//! The pseudo-classes and pseudo-elements supported by the style system.
#![deny(missing_docs)]
use cssparser::Parser as CssParser;
use matching::{common_style_affecting_attributes, CommonStyleAffectingAttributeMode};
use selectors::Element;
@ -11,6 +13,8 @@ use selectors::parser::{AttrSelector, SelectorList};
use std::fmt::Debug;
use stylesheets::{Origin, Namespaces};
/// A convenient alias for the type that represents an attribute value used for
/// selector parser implementation.
pub type AttrValue = <SelectorImpl as ::selectors::SelectorImpl>::AttrValue;
#[cfg(feature = "servo")]
@ -31,19 +35,30 @@ pub use servo::restyle_damage::ServoRestyleDamage as RestyleDamage;
#[cfg(feature = "gecko")]
pub use gecko::restyle_damage::GeckoRestyleDamage as RestyleDamage;
/// A type that represents the previous computed values needed for restyle
/// damage calculation.
#[cfg(feature = "servo")]
pub type PreExistingComputedValues = ::std::sync::Arc<::properties::ServoComputedValues>;
/// A type that represents the previous computed values needed for restyle
/// damage calculation.
#[cfg(feature = "gecko")]
pub type PreExistingComputedValues = ::gecko_bindings::structs::nsStyleContext;
/// Servo's selector parser.
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
pub struct SelectorParser<'a> {
/// The origin of the stylesheet we're parsing.
pub stylesheet_origin: Origin,
/// The namespace set of the stylesheet.
pub namespaces: &'a Namespaces,
}
impl<'a> SelectorParser<'a> {
/// Parse a selector list with an author origin and without taking into
/// account namespaces.
///
/// This is used for some DOM APIs like `querySelector`.
pub fn parse_author_origin_no_namespace(input: &str)
-> Result<SelectorList<SelectorImpl>, ()> {
let namespaces = Namespaces::default();
@ -54,68 +69,79 @@ impl<'a> SelectorParser<'a> {
SelectorList::parse(&parser, &mut CssParser::new(input))
}
/// Whether we're parsing selectors in a user-agent stylesheet.
pub fn in_user_agent_stylesheet(&self) -> bool {
matches!(self.stylesheet_origin, Origin::UserAgent)
}
}
/// This function determines if a pseudo-element is eagerly cascaded or not.
/// This enumeration determines if a pseudo-element is eagerly cascaded or not.
///
/// Eagerly cascaded pseudo-elements are "normal" pseudo-elements (i.e.
/// `::before` and `::after`). They inherit styles normally as another
/// selector would do, and they're part of the cascade.
///
/// Lazy pseudo-elements are affected by selector matching, but they're only
/// computed when needed, and not before. They're useful for general
/// pseudo-elements that are not very common.
///
/// Note that in Servo lazy pseudo-elements are restricted to a subset of
/// selectors, so you can't use it for public pseudo-elements. This is not the
/// case with Gecko though.
///
/// Precomputed ones skip the cascade process entirely, mostly as an
/// optimisation since they are private pseudo-elements (like
/// `::-servo-details-content`).
///
/// This pseudo-elements are resolved on the fly using *only* global rules
/// (rules of the form `*|*`), and applying them to the parent style.
///
/// If you're implementing a public selector that the end-user might customize,
/// then you probably need to make it eager.
/// If you're implementing a public selector for `Servo` that the end-user might
/// customize, then you probably need to make it eager.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum PseudoElementCascadeType {
/// Eagerly cascaded pseudo-elements are "normal" pseudo-elements (i.e.
/// `::before` and `::after`). They inherit styles normally as another
/// selector would do, and they're computed as part of the cascade.
Eager,
/// Lazy pseudo-elements are affected by selector matching, but they're only
/// computed when needed, and not before. They're useful for general
/// pseudo-elements that are not very common.
///
/// Note that in Servo lazy pseudo-elements are restricted to a subset of
/// selectors, so you can't use it for public pseudo-elements. This is not
/// the case with Gecko though.
Lazy,
/// Precomputed pseudo-elements skip the cascade process entirely, mostly as
/// an optimisation since they are private pseudo-elements (like
/// `::-servo-details-content`).
///
/// This pseudo-elements are resolved on the fly using *only* global rules
/// (rules of the form `*|*`), and applying them to the parent style.
Precomputed,
}
impl PseudoElementCascadeType {
/// Simple accessor to check whether the cascade type is eager.
#[inline]
pub fn is_eager(&self) -> bool {
*self == PseudoElementCascadeType::Eager
}
/// Simple accessor to check whether the cascade type is lazy.
#[inline]
pub fn is_lazy(&self) -> bool {
*self == PseudoElementCascadeType::Lazy
}
/// Simple accessor to check whether the cascade type is precomputed.
#[inline]
pub fn is_precomputed(&self) -> bool {
*self == PseudoElementCascadeType::Precomputed
}
}
/// An extension to rust-selector's `Element` trait.
pub trait ElementExt: Element<Impl=SelectorImpl> + Debug {
/// Whether this element is a `link`.
fn is_link(&self) -> bool;
/// Whether this element should match user and author rules.
///
/// We use this for Native Anonymous Content in Gecko.
fn matches_user_and_author_rules(&self) -> bool;
}
impl SelectorImpl {
/// A helper to traverse each eagerly cascaded pseudo-element, executing
/// `fun` on it.
///
/// TODO(emilio): We can optimize this for Gecko using the pseudo-element
/// macro, and we should consider doing that for Servo too.
#[inline]
pub fn each_eagerly_cascaded_pseudo_element<F>(mut fun: F)
where F: FnMut(PseudoElement)
where F: FnMut(PseudoElement),
{
Self::each_pseudo_element(|pseudo| {
if Self::pseudo_element_cascade_type(&pseudo).is_eager() {
@ -124,9 +150,14 @@ impl SelectorImpl {
})
}
/// A helper to traverse each precomputed pseudo-element, executing `fun` on
/// it.
///
/// The optimization comment in `each_eagerly_cascaded_pseudo_element` also
/// applies here.
#[inline]
pub fn each_precomputed_pseudo_element<F>(mut fun: F)
where F: FnMut(PseudoElement)
where F: FnMut(PseudoElement),
{
Self::each_pseudo_element(|pseudo| {
if Self::pseudo_element_cascade_type(&pseudo).is_precomputed() {
@ -136,6 +167,11 @@ impl SelectorImpl {
}
}
/// Checks whether we can share style if an element matches a given
/// attribute-selector that checks for existence (`[attr_name]`) easily.
///
/// We could do the same thing that we do for sibling rules and keep optimizing
/// these common attributes, but we'd have to measure how common it is.
pub fn attr_exists_selector_is_shareable(attr_selector: &AttrSelector<SelectorImpl>) -> bool {
// NB(pcwalton): If you update this, remember to update the corresponding list in
// `can_share_style_with()` as well.
@ -147,6 +183,12 @@ pub fn attr_exists_selector_is_shareable(attr_selector: &AttrSelector<SelectorIm
})
}
/// Checks whether we can share style if an element matches a given
/// attribute-selector that checks for equality (`[attr_name="attr_value"]`)
/// easily.
///
/// We could do the same thing that we do for sibling rules and keep optimizing
/// these common attributes, but we'd have to measure how common it is.
pub fn attr_equals_selector_is_shareable(attr_selector: &AttrSelector<SelectorImpl>,
value: &AttrValue) -> bool {
// FIXME(pcwalton): Remove once we start actually supporting RTL text. This is in

14
components/style/stylist.rs
View file

@ -8,8 +8,7 @@
use {Atom, LocalName};
use data::ComputedStyle;
use dom::PresentationalHintsSynthetizer;
use element_state::*;
use dom::{PresentationalHintsSynthetizer, TElement};
use error_reporting::StdoutErrorReporter;
use keyframes::KeyframesAnimation;
use media_queries::{Device, MediaType};
@ -662,16 +661,11 @@ impl Stylist {
/// restyle we need to do.
pub fn compute_restyle_hint<E>(&self,
element: &E,
snapshot: &Snapshot,
// NB: We need to pass current_state as an argument because
// selectors::Element doesn't provide access to ElementState
// directly, and computing it from the ElementState would be
// more expensive than getting it directly from the caller.
current_state: ElementState)
snapshot: &Snapshot)
-> RestyleHint
where E: ElementExt + Clone,
where E: TElement,
{
self.state_deps.compute_hint(element, snapshot, current_state)
self.state_deps.compute_hint(element, snapshot)
}
}