servo/components/style/properties/computed_value_flags.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 https://mozilla.org/MPL/2.0/. */

//! Misc information about a given computed style.

bitflags! {
    /// Misc information about a given computed style.
    ///
    /// All flags are currently inherited for text, pseudo elements, and
    /// anonymous boxes, see StyleBuilder::for_inheritance and its callsites.
    /// If we ever want to add some flags that shouldn't inherit for them,
    /// we might want to add a function to handle this.
    #[repr(C)]
    pub struct ComputedValueFlags: u16 {
        /// Whether the style or any of the ancestors has a text-decoration-line
        /// property that should get propagated to descendants.
        ///
        /// text-decoration-line is a reset property, but gets propagated in the
        /// frame/box tree.
        const HAS_TEXT_DECORATION_LINES = 1 << 0;

        /// Whether line break inside should be suppressed.
        ///
        /// If this flag is set, the line should not be broken inside,
        /// which means inlines act as if nowrap is set, <br> element is
        /// suppressed, and blocks are inlinized.
        ///
        /// This bit is propagated to all children of line participants.
        /// It is currently used by ruby to make its content unbreakable.
        const SHOULD_SUPPRESS_LINEBREAK = 1 << 1;

        /// A flag used to mark text that that has text-combine-upright.
        ///
        /// This is used from Gecko's layout engine.
        const IS_TEXT_COMBINED = 1 << 2;

        /// A flag used to mark styles under a relevant link that is also
        /// visited.
        const IS_RELEVANT_LINK_VISITED = 1 << 3;

        /// A flag used to mark styles which are a pseudo-element or under one.
        const IS_IN_PSEUDO_ELEMENT_SUBTREE = 1 << 4;

        /// Whether this style inherits the `display` property.
        ///
        /// This is important because it may affect our optimizations to avoid
        /// computing the style of pseudo-elements, given whether the
        /// pseudo-element is generated depends on the `display` value.
        const INHERITS_DISPLAY = 1 << 6;

        /// Whether this style inherits the `content` property.
        ///
        /// Important because of the same reason.
        const INHERITS_CONTENT = 1 << 7;

        /// Whether the child explicitly inherits any reset property.
        const INHERITS_RESET_STYLE = 1 << 8;

        /// Whether any value on our style is font-metric-dependent.
        const DEPENDS_ON_FONT_METRICS = 1 << 9;

        /// Whether the style or any of the ancestors has a multicol style.
        ///
        /// Only used in Servo.
        const CAN_BE_FRAGMENTED = 1 << 10;

        /// Whether this style is the style of the document element.
        const IS_ROOT_ELEMENT_STYLE = 1 << 11;

        /// Whether this element is inside an `opacity: 0` subtree.
        const IS_IN_OPACITY_ZERO_SUBTREE = 1 << 12;

        /// Whether there are author-specified rules for border-* properties
        /// (except border-image-*), background-color, or background-image.
        ///
        /// TODO(emilio): Maybe do include border-image, see:
        ///
        /// https://github.com/w3c/csswg-drafts/issues/4777#issuecomment-604424845
        const HAS_AUTHOR_SPECIFIED_BORDER_BACKGROUND = 1 << 13;

        /// Whether there are author-specified rules for padding-* properties.
        ///
        /// FIXME(emilio): Try to merge this with BORDER_BACKGROUND, see
        /// https://github.com/w3c/csswg-drafts/issues/4777
        const HAS_AUTHOR_SPECIFIED_PADDING = 1 << 14;
    }
}

impl ComputedValueFlags {
    /// Flags that are unconditionally propagated to descendants.
    #[inline]
    fn inherited_flags() -> Self {
        Self::IS_RELEVANT_LINK_VISITED |
            Self::CAN_BE_FRAGMENTED |
            Self::IS_IN_PSEUDO_ELEMENT_SUBTREE |
            Self::HAS_TEXT_DECORATION_LINES |
            Self::IS_IN_OPACITY_ZERO_SUBTREE
    }

    /// Flags that may be propagated to descendants.
    #[inline]
    fn maybe_inherited_flags() -> Self {
        Self::inherited_flags() | ComputedValueFlags::SHOULD_SUPPRESS_LINEBREAK
    }

    /// Returns the flags that are always propagated to descendants.
    ///
    /// See StyleAdjuster::set_bits and StyleBuilder.
    #[inline]
    pub fn inherited(self) -> Self {
        self & Self::inherited_flags()
    }

    /// Flags that are conditionally propagated to descendants, just to handle
    /// properly style invalidation.
    #[inline]
    pub fn maybe_inherited(self) -> Self {
        self & Self::maybe_inherited_flags()
    }
}