servo/components/style/data.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! Per-node data used in style calculation.

use dom::TRestyleDamage;
use properties::ComputedValues;
use properties::longhands::display::computed_value as display;
use restyle_hints::RestyleHint;
use rule_tree::StrongRuleNode;
use selector_parser::{PseudoElement, RestyleDamage, Snapshot};
use std::collections::HashMap;
use std::fmt;
use std::hash::BuildHasherDefault;
use std::mem;
use std::ops::{Deref, DerefMut};
use std::sync::Arc;

#[derive(Clone)]
pub struct ComputedStyle {
    /// The rule node representing the ordered list of rules matched for this
    /// node.
    pub rules: StrongRuleNode,

    /// The computed values for each property obtained by cascading the
    /// matched rules.
    pub values: Arc<ComputedValues>,
}

impl ComputedStyle {
    pub fn new(rules: StrongRuleNode, values: Arc<ComputedValues>) -> Self {
        ComputedStyle {
            rules: rules,
            values: values,
        }
    }
}

// We manually implement Debug for ComputedStyle so tht we can avoid the verbose
// stringification of ComputedValues for normal logging.
impl fmt::Debug for ComputedStyle {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "ComputedStyle {{ rules: {:?}, values: {{..}} }}", self.rules)
    }
}

type PseudoStylesInner = HashMap<PseudoElement, ComputedStyle,
                                 BuildHasherDefault<::fnv::FnvHasher>>;
#[derive(Clone, Debug)]
pub struct PseudoStyles(PseudoStylesInner);

impl PseudoStyles {
    pub fn empty() -> Self {
        PseudoStyles(HashMap::with_hasher(Default::default()))
    }
}

impl Deref for PseudoStyles {
    type Target = PseudoStylesInner;
    fn deref(&self) -> &Self::Target { &self.0 }
}

impl DerefMut for PseudoStyles {
    fn deref_mut(&mut self) -> &mut Self::Target { &mut self.0 }
}

/// The styles associated with a node, including the styles for any
/// pseudo-elements.
#[derive(Clone, Debug)]
pub struct ElementStyles {
    pub primary: ComputedStyle,
    pub pseudos: PseudoStyles,
}

impl ElementStyles {
    pub fn new(primary: ComputedStyle) -> Self {
        ElementStyles {
            primary: primary,
            pseudos: PseudoStyles::empty(),
        }
    }

    pub fn is_display_none(&self) -> bool {
        self.primary.values.get_box().clone_display() == display::T::none
    }
}

/// Enum to describe the different requirements that a restyle hint may impose
/// on its descendants.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum DescendantRestyleHint {
    /// This hint does not require any descendants to be restyled.
    Empty,
    /// This hint requires direct children to be restyled.
    Children,
    /// This hint requires all descendants to be restyled.
    Descendants,
}

impl DescendantRestyleHint {
    /// Propagates this descendant behavior to a child element.
    fn propagate(self) -> Self {
        use self::DescendantRestyleHint::*;
        if self == Descendants {
            Descendants
        } else {
            Empty
        }
    }

    fn union(self, other: Self) -> Self {
        use self::DescendantRestyleHint::*;
        if self == Descendants || other == Descendants {
            Descendants
        } else if self == Children || other == Children {
            Children
        } else {
            Empty
        }
    }
}

/// Restyle hint for storing on ElementData. We use a separate representation
/// to provide more type safety while propagating restyle hints down the tree.
#[derive(Clone, Debug)]
pub struct StoredRestyleHint {
    pub restyle_self: bool,
    pub descendants: DescendantRestyleHint,
}

impl StoredRestyleHint {
    /// Propagates this restyle hint to a child element.
    pub fn propagate(&self) -> Self {
        StoredRestyleHint {
            restyle_self: self.descendants == DescendantRestyleHint::Empty,
            descendants: self.descendants.propagate(),
        }
    }

    pub fn empty() -> Self {
        StoredRestyleHint {
            restyle_self: false,
            descendants: DescendantRestyleHint::Empty,
        }
    }

    pub fn subtree() -> Self {
        StoredRestyleHint {
            restyle_self: true,
            descendants: DescendantRestyleHint::Descendants,
        }
    }

    pub fn is_empty(&self) -> bool {
        !self.restyle_self && self.descendants == DescendantRestyleHint::Empty
    }

    pub fn insert(&mut self, other: &Self) {
        self.restyle_self = self.restyle_self || other.restyle_self;
        self.descendants = self.descendants.union(other.descendants);
    }
}

impl Default for StoredRestyleHint {
    fn default() -> Self {
        StoredRestyleHint {
            restyle_self: false,
            descendants: DescendantRestyleHint::Empty,
        }
    }
}

impl From<RestyleHint> for StoredRestyleHint {
    fn from(hint: RestyleHint) -> Self {
        use restyle_hints::*;
        use self::DescendantRestyleHint::*;
        debug_assert!(!hint.contains(RESTYLE_LATER_SIBLINGS), "Caller should apply sibling hints");
        StoredRestyleHint {
            restyle_self: hint.contains(RESTYLE_SELF),
            descendants: if hint.contains(RESTYLE_DESCENDANTS) { Descendants } else { Empty },
        }
    }
}

#[derive(Debug)]
pub enum RestyleDataStyles {
    Previous(ElementStyles),
    New(ElementStyles),
}

/// Transient data used by the restyle algorithm. This structure is instantiated
/// either before or during restyle traversal, and is cleared at the end of node
/// processing.
#[derive(Debug)]
pub struct RestyleData {
    pub styles: RestyleDataStyles,
    pub hint: StoredRestyleHint,
    pub damage: RestyleDamage,
    pub snapshot: Option<Snapshot>,
}

impl RestyleData {
    fn new(previous: ElementStyles) -> Self {
        RestyleData {
            styles: RestyleDataStyles::Previous(previous),
            hint: StoredRestyleHint::default(),
            damage: RestyleDamage::empty(),
            snapshot: None,
        }
    }

    pub fn get_current_styles(&self) -> Option<&ElementStyles> {
        use self::RestyleDataStyles::*;
        match self.styles {
            Previous(_) => None,
            New(ref x) => Some(x),
        }
    }

    pub fn current_styles(&self) -> &ElementStyles {
        self.get_current_styles().unwrap()
    }

    pub fn current_styles_mut(&mut self) -> &mut ElementStyles {
        use self::RestyleDataStyles::*;
        match self.styles {
            New(ref mut x) => x,
            Previous(_) => panic!("Calling current_styles_mut before styling"),
        }
    }

    pub fn current_or_previous_styles(&self) -> &ElementStyles {
        use self::RestyleDataStyles::*;
        match self.styles {
            Previous(ref x) => x,
            New(ref x) => x,
        }
    }

    fn finish_styling(&mut self, styles: ElementStyles, damage: RestyleDamage) {
        debug_assert!(self.get_current_styles().is_none());
        self.styles = RestyleDataStyles::New(styles);
        self.damage |= damage;
    }
}

/// Style system data associated with a node.
///
/// In Gecko, this hangs directly off a node, but is dropped when the frame takes
/// ownership of the computed style data.
///
/// In Servo, this is embedded inside of layout data, which itself hangs directly
/// off the node. Servo does not currently implement ownership transfer of the
/// computed style data to the frame.
///
/// In both cases, it is wrapped inside an AtomicRefCell to ensure thread
/// safety.
#[derive(Debug)]
pub enum ElementData {
    Initial(Option<ElementStyles>),
    Restyle(RestyleData),
    Persistent(ElementStyles),
}

impl ElementData {
    pub fn new(existing: Option<ElementStyles>) -> Self {
        if let Some(s) = existing {
            ElementData::Persistent(s)
        } else {
            ElementData::Initial(None)
        }
    }

    pub fn is_initial(&self) -> bool {
        match *self {
            ElementData::Initial(_) => true,
            _ => false,
        }
    }

    pub fn is_unstyled_initial(&self) -> bool {
        match *self {
            ElementData::Initial(None) => true,
            _ => false,
        }
    }

    pub fn is_styled_initial(&self) -> bool {
        match *self {
            ElementData::Initial(Some(_)) => true,
            _ => false,
        }
    }

    pub fn is_restyle(&self) -> bool {
        match *self {
            ElementData::Restyle(_) => true,
            _ => false,
        }
    }

    pub fn as_restyle(&self) -> Option<&RestyleData> {
        match *self {
            ElementData::Restyle(ref x) => Some(x),
            _ => None,
        }
    }

    pub fn as_restyle_mut(&mut self) -> Option<&mut RestyleData> {
        match *self {
            ElementData::Restyle(ref mut x) => Some(x),
            _ => None,
        }
    }

    pub fn is_persistent(&self) -> bool {
        match *self {
            ElementData::Persistent(_) => true,
            _ => false,
        }
    }

    /// Sets an element up for restyle, returning None for an unstyled element.
    pub fn restyle(&mut self) -> Option<&mut RestyleData> {
        if self.is_unstyled_initial() {
            return None;
        }

        // If the caller never consumed the initial style, make sure that the
        // change hint represents the delta from zero, rather than a delta from
        // a previous style that was never observed. Ideally this shouldn't
        // happen, but we handle it for robustness' sake.
        let damage_override = if self.is_styled_initial() {
            RestyleDamage::rebuild_and_reflow()
        } else {
            RestyleDamage::empty()
        };

        if !self.is_restyle() {
            // Play some tricks to reshape the enum without cloning ElementStyles.
            let old = mem::replace(self, ElementData::new(None));
            let styles = match old {
                ElementData::Initial(Some(s)) => s,
                ElementData::Persistent(s) => s,
                _ => unreachable!()
            };
            *self = ElementData::Restyle(RestyleData::new(styles));
        }

        let restyle = self.as_restyle_mut().unwrap();
        restyle.damage |= damage_override;
        Some(restyle)
    }

    /// Converts Initial and Restyle to Persistent. No-op for Persistent.
    pub fn persist(&mut self) {
        if self.is_persistent() {
            return;
        }

        // Play some tricks to reshape the enum without cloning ElementStyles.
        let old = mem::replace(self, ElementData::new(None));
        let styles = match old {
            ElementData::Initial(i) => i.unwrap(),
            ElementData::Restyle(r) => match r.styles {
                RestyleDataStyles::New(n) => n,
                RestyleDataStyles::Previous(_) => panic!("Never restyled element"),
            },
            ElementData::Persistent(_) => unreachable!(),
        };
        *self = ElementData::Persistent(styles);
    }

    pub fn damage(&self) -> RestyleDamage {
        use self::ElementData::*;
        match *self {
            Initial(ref s) => {
                debug_assert!(s.is_some());
                RestyleDamage::rebuild_and_reflow()
            },
            Restyle(ref r) => {
                debug_assert!(r.get_current_styles().is_some());
                r.damage
            },
            Persistent(_) => RestyleDamage::empty(),
        }
    }

    // A version of the above, with the assertions replaced with warnings to
    // be more robust in corner-cases. This will go away soon.
    #[cfg(feature = "gecko")]
    pub fn damage_sloppy(&self) -> RestyleDamage {
        use self::ElementData::*;
        match *self {
            Initial(ref s) => {
                if s.is_none() {
                    error!("Accessing damage on unstyled element");
                }
                RestyleDamage::rebuild_and_reflow()
            },
            Restyle(ref r) => {
                if r.get_current_styles().is_none() {
                    error!("Accessing damage on dirty element");
                }
                r.damage
            },
            Persistent(_) => RestyleDamage::empty(),
        }
    }

    pub fn current_styles(&self) -> &ElementStyles {
        self.get_current_styles().unwrap()
    }

    pub fn get_current_styles(&self) -> Option<&ElementStyles> {
        use self::ElementData::*;
        match *self {
            Initial(ref x) => x.as_ref(),
            Restyle(ref x) => x.get_current_styles(),
            Persistent(ref x) => Some(x),
        }
    }

    pub fn current_styles_mut(&mut self) -> &mut ElementStyles {
        use self::ElementData::*;
        match *self {
            Initial(ref mut x) => x.as_mut().unwrap(),
            Restyle(ref mut x) => x.current_styles_mut(),
            Persistent(ref mut x) => x,
        }
    }

    pub fn previous_styles(&self) -> Option<&ElementStyles> {
        use self::ElementData::*;
        use self::RestyleDataStyles::*;
        match *self {
            Initial(_) => None,
            Restyle(ref x) => match x.styles {
                Previous(ref styles) => Some(styles),
                New(_) => panic!("Calling previous_styles after finish_styling"),
            },
            Persistent(_) => panic!("Calling previous_styles on Persistent ElementData"),
        }
    }

    pub fn previous_styles_mut(&mut self) -> Option<&mut ElementStyles> {
        use self::ElementData::*;
        use self::RestyleDataStyles::*;
        match *self {
            Initial(_) => None,
            Restyle(ref mut x) => match x.styles {
                Previous(ref mut styles) => Some(styles),
                New(_) => panic!("Calling previous_styles after finish_styling"),
            },
            Persistent(_) => panic!("Calling previous_styles on Persistent ElementData"),
        }
    }

    pub fn current_or_previous_styles(&self) -> &ElementStyles {
        use self::ElementData::*;
        match *self {
            Initial(ref x) => x.as_ref().unwrap(),
            Restyle(ref x) => x.current_or_previous_styles(),
            Persistent(ref x) => x,
        }
    }

    pub fn finish_styling(&mut self, styles: ElementStyles, damage: RestyleDamage) {
        use self::ElementData::*;
        match *self {
            Initial(ref mut x) => {
                debug_assert!(x.is_none());
                debug_assert!(damage == RestyleDamage::rebuild_and_reflow());
                *x = Some(styles);
            },
            Restyle(ref mut x) => x.finish_styling(styles, damage),
            Persistent(_) => panic!("Calling finish_styling on Persistent ElementData"),
        };
    }
}