components/layout/formatting_contexts.rs - main - githubmirror/servo

components/layout/formatting_contexts.rs
636 строк24 KB
Oriol Brufau
layout: Implement block-axis centering for buttons (#46590)
19 июл 2026, 10:25
19 июл 2026, 10:255f837eb
/* 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/. */

use app_units::Au;
use atomic_refcell::AtomicRefCell;
use layout_api::LayoutNode;
use malloc_size_of_derive::MallocSizeOf;
use script::layout_dom::{ServoDangerousStyleElement, ServoLayoutNode};
use servo_arc::Arc;
use style::context::SharedStyleContext;
use style::logical_geometry::Direction;
use style::properties::ComputedValues;
use style::selector_parser::PseudoElement;

use crate::context::LayoutContext;
use crate::dom::WeakLayoutBox;
use crate::dom_traversal::{Contents, NodeAndStyleInfo, NonReplacedContents};
use crate::flexbox::FlexContainer;
use crate::flow::BlockFormattingContext;
use crate::fragment_tree::{BaseFragmentInfo, FragmentFlags};
use crate::layout_box_base::{IndependentFormattingContextLayoutResult, LayoutBoxBase};
use crate::positioned::{LayoutRootLayoutInputs, PositioningContext};
use crate::replaced::ReplacedContents;
use crate::sizing::{
    self, ComputeInlineContentSizes, ContentSizes, InlineContentSizesResult, LazySize,
};
use crate::style_ext::{AspectRatio, Display, DisplayInside, LayoutStyle};
use crate::table::Table;
use crate::taffy::TaffyContainer;
use crate::{
    ArcRefCell, ConstraintSpace, ContainingBlock, IndefiniteContainingBlock, LogicalVec2,
    PropagatedBoxTreeData,
};

/// <https://drafts.csswg.org/css-display/#independent-formatting-context>
#[derive(Debug, MallocSizeOf)]
pub(crate) struct IndependentFormattingContext {
    pub base: LayoutBoxBase,
    // Private so that code outside of this module cannot match variants.
    // It should go through methods instead.
    contents: IndependentFormattingContextContents,
    /// Data that was originally propagated down to this [`IndependentFormattingContext`]
    /// during creation. This is used during incremental layout.
    pub propagated_data: PropagatedBoxTreeData,
    /// If this [`IndependentFormattingContext`] was a layout root, this stores the data
    /// necessary to lay it out again.
    pub layout_root_layout_inputs: AtomicRefCell<Option<Box<LayoutRootLayoutInputs>>>,
}

#[derive(Debug, MallocSizeOf)]
pub(crate) enum IndependentFormattingContextContents {
    // Additionally to the replaced contents, replaced boxes may have an inner widget.
    Replaced(
        ReplacedContents,
        Option<ArcRefCell<IndependentFormattingContext>>,
    ),
    Flow(BlockFormattingContext),
    Flex(FlexContainer),
    Grid(TaffyContainer),
    Table(Table),
    // Other layout modes go here
}

impl IndependentFormattingContextContents {
    fn subtree_size(&self) -> usize {
        match self {
            IndependentFormattingContextContents::Replaced(_, widget) => widget
                .as_ref()
                .map_or(0, |widget| widget.borrow().subtree_size()),
            IndependentFormattingContextContents::Flow(block_formatting_context) => {
                block_formatting_context.contents.subtree_size()
            },
            IndependentFormattingContextContents::Flex(flex_container) => {
                flex_container.subtree_size()
            },
            IndependentFormattingContextContents::Grid(taffy_container) => {
                taffy_container.subtree_size()
            },
            IndependentFormattingContextContents::Table(table) => table.subtree_size(),
        }
    }
}

/// The baselines of a layout or a [`crate::fragment_tree::BoxFragment`]. Some layout
/// uses the first and some layout uses the last.
#[derive(Clone, Copy, Debug, Default, MallocSizeOf)]
pub(crate) struct Baselines {
    pub first: Option<Au>,
    pub last: Option<Au>,
}

impl Baselines {
    pub(crate) fn offset(&self, block_offset: Au) -> Baselines {
        Self {
            first: self.first.map(|first| first + block_offset),
            last: self.last.map(|last| last + block_offset),
        }
    }
}

impl IndependentFormattingContext {
    pub(crate) fn new(
        base: LayoutBoxBase,
        contents: IndependentFormattingContextContents,
        propagated_data: PropagatedBoxTreeData,
    ) -> Self {
        base.set_subtree_size(contents.subtree_size() + 1);
        Self {
            base,
            contents,
            propagated_data,
            layout_root_layout_inputs: None.into(),
        }
    }

    pub(crate) fn rebuild(
        &mut self,
        layout_context: &LayoutContext,
        node_and_style_info: &NodeAndStyleInfo,
    ) {
        let contents = Contents::for_element(node_and_style_info.node, layout_context);
        let display = match Display::from(node_and_style_info.style.get_box().display) {
            Display::None | Display::Contents => {
                unreachable!("Should never try to rebuild IndependentFormattingContext with no box")
            },
            Display::GeneratingBox(display) => {
                display.used_value_for_contents(&contents, node_and_style_info)
            },
        };

        // This ensures that the `FragmentFlags` of this `BaseFragmentInfo` reflect the
        // current layout and not the set that was calculated during previous layouts.
        self.base.base_fragment_info = node_and_style_info.into();

        self.contents = Self::construct_contents(
            layout_context,
            node_and_style_info,
            &mut self.base.base_fragment_info,
            display.display_inside(),
            contents,
            self.propagated_data,
        );

        self.base.clear_fragments_and_dirty_fragment_cache();
        *self.base.cached_inline_content_size.borrow_mut() = None;
        self.base.repair_style(&node_and_style_info.style);
    }

    pub(crate) fn construct(
        context: &LayoutContext,
        node_and_style_info: &NodeAndStyleInfo,
        display_inside: DisplayInside,
        contents: Contents,
        propagated_data: PropagatedBoxTreeData,
    ) -> Self {
        let mut base_fragment_info: BaseFragmentInfo = node_and_style_info.into();
        let contents = Self::construct_contents(
            context,
            node_and_style_info,
            &mut base_fragment_info,
            display_inside,
            contents,
            propagated_data,
        );

        let base = LayoutBoxBase::new(base_fragment_info, node_and_style_info.style.clone());
        base.set_subtree_size(contents.subtree_size() + 1);

        Self {
            base,
            contents,
            propagated_data,
            layout_root_layout_inputs: None.into(),
        }
    }

    fn construct_contents(
        context: &LayoutContext,
        node_and_style_info: &NodeAndStyleInfo,
        base_fragment_info: &mut BaseFragmentInfo,
        display_inside: DisplayInside,
        contents: Contents,
        propagated_data: PropagatedBoxTreeData,
    ) -> IndependentFormattingContextContents {
        let non_replaced_contents = match contents {
            Contents::Replaced(contents) => {
                base_fragment_info.flags.insert(FragmentFlags::IS_REPLACED);

                // Some replaced elements can have inner widgets, e.g. `<video controls>`.
                let node = node_and_style_info.node;
                let should_make_widget = node.pseudo_element_chain().is_empty() &&
                    node.is_root_of_user_agent_widget() &&
                    !contents.is_content_replacement;
                let widget = should_make_widget.then(|| {
                    let widget_info = node_and_style_info
                        .with_pseudo_element(context, PseudoElement::ServoAnonymousBox)
                        .expect("Should always be able to construct info for anonymous boxes.");
                    // Use a block formatting context for the widget, since the display inside is always flow.
                    let widget_contents = IndependentFormattingContextContents::Flow(
                        BlockFormattingContext::construct(
                            context,
                            &widget_info,
                            NonReplacedContents::OfElement,
                            propagated_data,
                            false, /* is_list_item */
                        ),
                    );
                    let widget_base = LayoutBoxBase::new((&widget_info).into(), widget_info.style);
                    ArcRefCell::new(IndependentFormattingContext::new(
                        widget_base,
                        widget_contents,
                        propagated_data,
                    ))
                });

                return IndependentFormattingContextContents::Replaced(contents, widget);
            },
            Contents::Widget(non_replaced_contents) => {
                base_fragment_info.flags.insert(FragmentFlags::IS_WIDGET);
                non_replaced_contents
            },
            Contents::NonReplaced(non_replaced_contents) => non_replaced_contents,
        };

        match display_inside {
            DisplayInside::Flow { is_list_item } | DisplayInside::FlowRoot { is_list_item } => {
                IndependentFormattingContextContents::Flow(BlockFormattingContext::construct(
                    context,
                    node_and_style_info,
                    non_replaced_contents,
                    propagated_data,
                    is_list_item,
                ))
            },
            DisplayInside::Grid => {
                IndependentFormattingContextContents::Grid(TaffyContainer::construct(
                    context,
                    node_and_style_info,
                    non_replaced_contents,
                    propagated_data,
                ))
            },
            DisplayInside::Flex => {
                IndependentFormattingContextContents::Flex(FlexContainer::construct(
                    context,
                    node_and_style_info,
                    non_replaced_contents,
                    propagated_data,
                ))
            },
            DisplayInside::Table => {
                let table_grid_style = context
                    .style_context
                    .stylist
                    .style_for_anonymous::<ServoDangerousStyleElement>(
                        &context.style_context.guards,
                        &PseudoElement::ServoTableGrid,
                        &node_and_style_info.style,
                    );
                base_fragment_info.flags.insert(FragmentFlags::DO_NOT_PAINT);
                IndependentFormattingContextContents::Table(Table::construct(
                    context,
                    node_and_style_info,
                    table_grid_style,
                    non_replaced_contents,
                    propagated_data,
                ))
            },
        }
    }

    #[inline]
    pub fn style(&self) -> &Arc<ComputedValues> {
        &self.base.style
    }

    #[inline]
    pub fn base_fragment_info(&self) -> BaseFragmentInfo {
        self.base.base_fragment_info
    }

    pub(crate) fn inline_content_sizes(
        &self,
        layout_context: &LayoutContext,
        constraint_space: &ConstraintSpace,
    ) -> InlineContentSizesResult {
        self.base
            .inline_content_sizes(layout_context, constraint_space, &self.contents)
    }

    /// Computes the tentative intrinsic block sizes that may be needed while computing
    /// the intrinsic inline sizes. Therefore, this ignores the values of the sizing
    /// properties in both axes.
    /// A return value of `None` indicates that there is no suitable tentative intrinsic
    /// block size, so intrinsic keywords in the block sizing properties will be ignored,
    /// possibly resulting in an indefinite [`SizeConstraint`] for computing the intrinsic
    /// inline sizes and laying out the contents.
    /// A return value of `Some` indicates that intrinsic keywords in the block sizing
    /// properties will be resolved as the contained value, guaranteeing a definite amount
    /// for computing the intrinsic inline sizes and laying out the contents.
    pub(crate) fn tentative_block_content_size(
        &self,
        preferred_aspect_ratio: Option<AspectRatio>,
        inline_stretch_size: Au,
    ) -> Option<ContentSizes> {
        let result = self.tentative_block_content_size_with_dependency(
            preferred_aspect_ratio,
            inline_stretch_size,
        );
        Some(result?.0)
    }

    /// Same as [`Self::tentative_block_content_size()`], but if there is a tentative intrinsic
    /// block size, it also includes a bool which will be true if the former depends on
    /// the provided `inline_stretch_size`.
    pub(crate) fn tentative_block_content_size_with_dependency(
        &self,
        preferred_aspect_ratio: Option<AspectRatio>,
        inline_stretch_size: Au,
    ) -> Option<(ContentSizes, bool)> {
        // See <https://github.com/w3c/csswg-drafts/issues/12333> regarding the difference
        // in behavior for the replaced and non-replaced cases.
        match &self.contents {
            IndependentFormattingContextContents::Replaced(contents, _) => {
                // For replaced elements with no ratio, the returned value doesn't matter.
                let ratio = preferred_aspect_ratio?;
                let writing_mode = self.style().writing_mode;
                let natural_sizes = contents.logical_natural_sizes(writing_mode);
                let (block_size, depends_on_inline_stretch_size) =
                    match (natural_sizes.block, natural_sizes.inline) {
                        (Some(block_size), None) => (block_size, false),
                        (_, Some(inline_size)) => (
                            ratio.compute_dependent_size(Direction::Block, inline_size),
                            false,
                        ),
                        (None, None) => (
                            ratio.compute_dependent_size(Direction::Block, inline_stretch_size),
                            true,
                        ),
                    };
                Some((block_size.into(), depends_on_inline_stretch_size))
            },
            _ => None,
        }
    }

    pub(crate) fn outer_inline_content_sizes(
        &self,
        layout_context: &LayoutContext,
        containing_block: &IndefiniteContainingBlock,
        auto_minimum: &LogicalVec2<Au>,
        auto_block_size_stretches_to_containing_block: bool,
    ) -> InlineContentSizesResult {
        sizing::outer_inline(
            &self.base,
            &self.layout_style(),
            containing_block,
            auto_minimum,
            auto_block_size_stretches_to_containing_block,
            self.is_replaced(),
            true, /* establishes_containing_block */
            |padding_border_sums| self.preferred_aspect_ratio(padding_border_sums),
            |constraint_space| self.inline_content_sizes(layout_context, constraint_space),
            |preferred_aspect_ratio| {
                self.tentative_block_content_size(preferred_aspect_ratio, Au(0))
            },
        )
    }

    pub(crate) fn repair_style(
        &mut self,
        context: &SharedStyleContext,
        node: &ServoLayoutNode,
        new_style: &Arc<ComputedValues>,
    ) {
        self.base.repair_style(new_style);
        match &mut self.contents {
            IndependentFormattingContextContents::Replaced(_, widget) => {
                if let Some(widget) = widget {
                    let node = node
                        .with_pseudo(PseudoElement::ServoAnonymousBox)
                        .expect("Should always be able to construct info for anonymous boxes.");
                    widget.borrow_mut().repair_style(context, &node, new_style);
                }
            },
            IndependentFormattingContextContents::Flow(block_formatting_context) => {
                block_formatting_context.repair_style(context, node, new_style);
            },
            IndependentFormattingContextContents::Flex(flex_container) => {
                flex_container.repair_style(new_style)
            },
            IndependentFormattingContextContents::Grid(taffy_container) => {
                taffy_container.repair_style(new_style)
            },
            IndependentFormattingContextContents::Table(table) => {
                table.repair_style(context, new_style)
            },
        }
    }

    #[inline]
    pub(crate) fn is_block_container(&self) -> bool {
        matches!(self.contents, IndependentFormattingContextContents::Flow(_))
    }

    #[inline]
    pub(crate) fn is_replaced(&self) -> bool {
        matches!(
            self.contents,
            IndependentFormattingContextContents::Replaced(_, _)
        )
    }

    #[inline]
    pub(crate) fn is_table(&self) -> bool {
        matches!(
            &self.contents,
            IndependentFormattingContextContents::Table(_)
        )
    }

    #[inline]
    pub(crate) fn is_grid(&self) -> bool {
        matches!(
            &self.contents,
            IndependentFormattingContextContents::Grid(_)
        )
    }

    #[servo_tracing::instrument(
        name = "IndependentFormattingContext::layout_without_caching",
        skip_all
    )]
    fn layout_without_caching(
        &self,
        layout_context: &LayoutContext,
        positioning_context: &mut PositioningContext,
        containing_block_for_children: &ContainingBlock,
        containing_block: &ContainingBlock,
        preferred_aspect_ratio: Option<AspectRatio>,
        lazy_block_size: &LazySize,
    ) -> IndependentFormattingContextLayoutResult {
        match &self.contents {
            IndependentFormattingContextContents::Replaced(replaced, widget) => {
                let mut replaced_layout = replaced.layout(
                    layout_context,
                    containing_block_for_children,
                    preferred_aspect_ratio,
                    &self.base,
                    lazy_block_size,
                );
                if let Some(widget) = widget {
                    let mut widget_layout = widget.borrow().layout(
                        layout_context,
                        positioning_context,
                        containing_block_for_children,
                        containing_block_for_children,
                        None,
                        &LazySize::intrinsic(),
                    );
                    replaced_layout
                        .fragments
                        .append(&mut widget_layout.fragments);
                }
                replaced_layout
            },
            IndependentFormattingContextContents::Flow(bfc) => bfc.layout(
                layout_context,
                positioning_context,
                containing_block_for_children,
                lazy_block_size,
                Some(&self.base),
            ),
            IndependentFormattingContextContents::Flex(fc) => fc.layout(
                layout_context,
                positioning_context,
                containing_block_for_children,
                lazy_block_size,
            ),
            IndependentFormattingContextContents::Grid(fc) => fc.layout(
                layout_context,
                positioning_context,
                containing_block_for_children,
                containing_block,
            ),
            IndependentFormattingContextContents::Table(table) => table.layout(
                layout_context,
                positioning_context,
                containing_block_for_children,
                containing_block,
            ),
        }
    }

    pub(crate) fn layout_and_is_cached(
        &self,
        layout_context: &LayoutContext,
        positioning_context: &mut PositioningContext,
        containing_block_for_children: &ContainingBlock,
        containing_block: &ContainingBlock,
        preferred_aspect_ratio: Option<AspectRatio>,
        lazy_block_size: &LazySize,
    ) -> (IndependentFormattingContextLayoutResult, bool) {
        if let Some(cached_layout_result) = self
            .base
            .cached_independent_formatting_context_layout_if_applicable(
                positioning_context,
                containing_block_for_children,
            )
        {
            return (cached_layout_result, true);
        }

        #[cfg(feature = "tracing")]
        tracing::debug!(
            name: "IndependentFormattingContext::layout cache miss",
            required = ?containing_block_for_children.size,
        );
        let mut child_positioning_context = PositioningContext::default();
        let result = self.layout_without_caching(
            layout_context,
            &mut child_positioning_context,
            containing_block_for_children,
            containing_block,
            preferred_aspect_ratio,
            lazy_block_size,
        );
        self.base.cache_independent_formatting_context_layout(
            containing_block_for_children,
            &child_positioning_context,
            &result,
        );
        positioning_context.append(child_positioning_context);
        (result, false)
    }

    pub(crate) fn layout(
        &self,
        layout_context: &LayoutContext,
        positioning_context: &mut PositioningContext,
        containing_block_for_children: &ContainingBlock,
        containing_block: &ContainingBlock,
        preferred_aspect_ratio: Option<AspectRatio>,
        lazy_block_size: &LazySize,
    ) -> IndependentFormattingContextLayoutResult {
        self.layout_and_is_cached(
            layout_context,
            positioning_context,
            containing_block_for_children,
            containing_block,
            preferred_aspect_ratio,
            lazy_block_size,
        )
        .0
    }

    #[inline]
    pub(crate) fn layout_style(&self) -> LayoutStyle<'_> {
        match &self.contents {
            IndependentFormattingContextContents::Replaced(replaced, _) => {
                replaced.layout_style(&self.base)
            },
            IndependentFormattingContextContents::Flow(fc) => fc.layout_style(&self.base),
            IndependentFormattingContextContents::Flex(fc) => fc.layout_style(),
            IndependentFormattingContextContents::Grid(fc) => fc.layout_style(),
            IndependentFormattingContextContents::Table(fc) => fc.layout_style(None),
        }
    }

    #[inline]
    pub(crate) fn preferred_aspect_ratio(
        &self,
        padding_border_sums: &LogicalVec2<Au>,
    ) -> Option<AspectRatio> {
        match &self.contents {
            IndependentFormattingContextContents::Replaced(replaced, _) => {
                replaced.preferred_aspect_ratio(self.style(), padding_border_sums)
            },
            // TODO: support preferred aspect ratios on non-replaced boxes.
            _ => None,
        }
    }

    pub(crate) fn attached_to_tree(&self, layout_box: WeakLayoutBox) {
        match &self.contents {
            IndependentFormattingContextContents::Replaced(_, widget) => {
                if let Some(widget) = widget {
                    widget.borrow_mut().base.parent_box.replace(layout_box);
                }
            },
            IndependentFormattingContextContents::Flow(contents) => {
                contents.attached_to_tree(layout_box)
            },
            IndependentFormattingContextContents::Flex(contents) => {
                contents.attached_to_tree(layout_box)
            },
            IndependentFormattingContextContents::Grid(contents) => {
                contents.attached_to_tree(layout_box)
            },
            IndependentFormattingContextContents::Table(contents) => {
                contents.attached_to_tree(layout_box)
            },
        }
    }

    pub(crate) fn subtree_size(&self) -> usize {
        self.base.subtree_size()
    }
}

impl ComputeInlineContentSizes for IndependentFormattingContextContents {
    fn compute_inline_content_sizes(
        &self,
        layout_context: &LayoutContext,
        constraint_space: &ConstraintSpace,
    ) -> InlineContentSizesResult {
        match self {
            Self::Replaced(inner, _) => {
                inner.compute_inline_content_sizes(layout_context, constraint_space)
            },
            Self::Flow(inner) => inner
                .contents
                .compute_inline_content_sizes(layout_context, constraint_space),
            Self::Flex(inner) => {
                inner.compute_inline_content_sizes(layout_context, constraint_space)
            },
            Self::Grid(inner) => {
                inner.compute_inline_content_sizes(layout_context, constraint_space)
            },
            Self::Table(inner) => {
                inner.compute_inline_content_sizes(layout_context, constraint_space)
            },
        }
    }
}