path: root/components/layout_2020/flow/root.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/. */

use atomic_refcell::AtomicRef;
use script_layout_interface::wrapper_traits::LayoutNode;
use script_layout_interface::{LayoutElementType, LayoutNodeType};
use serde::Serialize;
use servo_arc::Arc;
use style::dom::OpaqueNode;
use style::properties::ComputedValues;
use style::values::computed::Length;
use style_traits::CSSPixel;

use crate::cell::ArcRefCell;
use crate::context::LayoutContext;
use crate::dom::{LayoutBox, NodeExt};
use crate::dom_traversal::{iter_child_nodes, Contents, NodeAndStyleInfo};
use crate::flexbox::FlexLevelBox;
use crate::flow::float::FloatBox;
use crate::flow::inline::InlineLevelBox;
use crate::flow::{BlockContainer, BlockFormattingContext, BlockLevelBox};
use crate::formatting_contexts::IndependentFormattingContext;
use crate::fragment_tree::FragmentTree;
use crate::geom::{LogicalVec2, PhysicalPoint, PhysicalRect, PhysicalSize};
use crate::positioned::{AbsolutelyPositionedBox, PositioningContext};
use crate::replaced::ReplacedContent;
use crate::style_ext::{ComputedValuesExt, Display, DisplayGeneratingBox, DisplayInside};
use crate::DefiniteContainingBlock;

#[derive(Serialize)]
pub struct BoxTree {
    /// Contains typically exactly one block-level box, which was generated by the root element.
    /// There may be zero if that element has `display: none`.
    root: BlockFormattingContext,

    /// https://drafts.csswg.org/css-backgrounds/#special-backgrounds
    canvas_background: CanvasBackground,
}

impl BoxTree {
    pub fn construct<'dom, Node>(context: &LayoutContext, root_element: Node) -> Self
    where
        Node: 'dom + Copy + LayoutNode<'dom> + Send + Sync,
    {
        let boxes = construct_for_root_element(&context, root_element);

        // Zero box for `:root { display: none }`, one for the root element otherwise.
        assert!(boxes.len() <= 1);

        let contents = BlockContainer::BlockLevelBoxes(boxes);
        let contains_floats = contents.contains_floats();
        Self {
            root: BlockFormattingContext {
                contents,
                contains_floats,
            },
            canvas_background: CanvasBackground::for_root_element(context, root_element),
        }
    }

    /// This method attempts to incrementally update the box tree from an
    /// arbitrary node that is not necessarily the document's root element.
    ///
    /// If the node is not a valid candidate for incremental update, the method
    /// loops over its parent. The only valid candidates for now are absolutely
    /// positioned boxes which don't change their outside display mode (i.e. it
    /// will not attempt to update from an absolutely positioned inline element
    /// which became an absolutely positioned block element). The value `true`
    /// is returned if an incremental update could be done, and `false`
    /// otherwise.
    ///
    /// There are various pain points that need to be taken care of to extend
    /// the set of valid candidates:
    /// * it is not obvious how to incrementally check whether a block
    ///   formatting context still contains floats or not;
    /// * the propagation of text decorations towards node descendants is
    ///   hard to do incrementally with our current representation of boxes
    /// * how intrinsic content sizes are computed eagerly makes it hard
    ///   to update those sizes for ancestors of the node from which we
    ///   made an incremental update.
    pub fn update<'dom, Node>(context: &LayoutContext, mut dirty_node: Node) -> bool
    where
        Node: 'dom + Copy + LayoutNode<'dom> + Send + Sync,
    {
        enum UpdatePoint {
            AbsolutelyPositionedBlockLevelBox(ArcRefCell<BlockLevelBox>),
            AbsolutelyPositionedInlineLevelBox(ArcRefCell<InlineLevelBox>),
            AbsolutelyPositionedFlexLevelBox(ArcRefCell<FlexLevelBox>),
        }

        fn update_point<'dom, Node>(
            node: Node,
        ) -> Option<(Arc<ComputedValues>, DisplayInside, UpdatePoint)>
        where
            Node: NodeExt<'dom>,
        {
            if !node.is_element() {
                return None;
            }

            if node.type_id() == LayoutNodeType::Element(LayoutElementType::HTMLBodyElement) {
                // This can require changes to the canvas background.
                return None;
            }

            // Don't update unstyled nodes.
            let data = node.get_style_and_layout_data()?;

            // Don't update nodes that have pseudo-elements.
            let element_data = data.style_data.element_data.borrow();
            if !element_data.styles.pseudos.is_empty() {
                return None;
            }

            let layout_data = data.layout_data.borrow();
            if layout_data.pseudo_before_box.borrow().is_some() {
                return None;
            }
            if layout_data.pseudo_after_box.borrow().is_some() {
                return None;
            }

            let primary_style = element_data.styles.primary();
            let box_style = primary_style.get_box();

            if !box_style.position.is_absolutely_positioned() {
                return None;
            }

            let display_inside = match Display::from(box_style.display) {
                Display::GeneratingBox(DisplayGeneratingBox::OutsideInside { inside, .. }) => {
                    inside
                },
                _ => return None,
            };

            let update_point =
                match &*AtomicRef::filter_map(layout_data.self_box.borrow(), Option::as_ref)? {
                    LayoutBox::DisplayContents => return None,
                    LayoutBox::BlockLevel(block_level_box) => match &*block_level_box.borrow() {
                        BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(_)
                            if box_style.position.is_absolutely_positioned() =>
                        {
                            UpdatePoint::AbsolutelyPositionedBlockLevelBox(block_level_box.clone())
                        },
                        _ => return None,
                    },
                    LayoutBox::InlineLevel(inline_level_box) => match &*inline_level_box.borrow() {
                        InlineLevelBox::OutOfFlowAbsolutelyPositionedBox(_)
                            if box_style.position.is_absolutely_positioned() =>
                        {
                            UpdatePoint::AbsolutelyPositionedInlineLevelBox(
                                inline_level_box.clone(),
                            )
                        },
                        _ => return None,
                    },
                    LayoutBox::FlexLevel(flex_level_box) => match &*flex_level_box.borrow() {
                        FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(_)
                            if box_style.position.is_absolutely_positioned() =>
                        {
                            UpdatePoint::AbsolutelyPositionedFlexLevelBox(flex_level_box.clone())
                        },
                        _ => return None,
                    },
                };
            Some((primary_style.clone(), display_inside, update_point))
        }

        loop {
            if let Some((primary_style, display_inside, update_point)) = update_point(dirty_node) {
                let contents = ReplacedContent::for_element(dirty_node)
                    .map_or(Contents::OfElement, Contents::Replaced);
                let info = NodeAndStyleInfo::new(dirty_node, Arc::clone(&primary_style));
                let out_of_flow_absolutely_positioned_box = ArcRefCell::new(
                    AbsolutelyPositionedBox::construct(context, &info, display_inside, contents),
                );
                match update_point {
                    UpdatePoint::AbsolutelyPositionedBlockLevelBox(block_level_box) => {
                        *block_level_box.borrow_mut() =
                            BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(
                                out_of_flow_absolutely_positioned_box,
                            );
                    },
                    UpdatePoint::AbsolutelyPositionedInlineLevelBox(inline_level_box) => {
                        *inline_level_box.borrow_mut() =
                            InlineLevelBox::OutOfFlowAbsolutelyPositionedBox(
                                out_of_flow_absolutely_positioned_box,
                            );
                    },
                    UpdatePoint::AbsolutelyPositionedFlexLevelBox(flex_level_box) => {
                        *flex_level_box.borrow_mut() =
                            FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(
                                out_of_flow_absolutely_positioned_box,
                            );
                    },
                }
                return true;
            }
            dirty_node = match dirty_node.parent_node() {
                Some(parent) => parent,
                None => return false,
            };
        }
    }
}

fn construct_for_root_element<'dom>(
    context: &LayoutContext,
    root_element: impl NodeExt<'dom>,
) -> Vec<ArcRefCell<BlockLevelBox>> {
    let info = NodeAndStyleInfo::new(root_element, root_element.style(context));
    let box_style = info.style.get_box();

    let display_inside = match Display::from(box_style.display) {
        Display::None => {
            root_element.unset_all_boxes();
            return Vec::new();
        },
        Display::Contents => {
            // Unreachable because the style crate adjusts the computed values:
            // https://drafts.csswg.org/css-display-3/#transformations
            // “'display' of 'contents' computes to 'block' on the root element”
            unreachable!()
        },
        // The root element is blockified, ignore DisplayOutside
        Display::GeneratingBox(DisplayGeneratingBox::OutsideInside { inside, .. }) => inside,
    };

    let contents =
        ReplacedContent::for_element(root_element).map_or(Contents::OfElement, Contents::Replaced);
    let root_box = if box_style.position.is_absolutely_positioned() {
        BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(ArcRefCell::new(
            AbsolutelyPositionedBox::construct(context, &info, display_inside, contents),
        ))
    } else if box_style.float.is_floating() {
        BlockLevelBox::OutOfFlowFloatBox(FloatBox::construct(
            context,
            &info,
            display_inside,
            contents,
        ))
    } else {
        let propagated_text_decoration_line = info.style.clone_text_decoration_line();
        BlockLevelBox::Independent(IndependentFormattingContext::construct(
            context,
            &info,
            display_inside,
            contents,
            propagated_text_decoration_line,
        ))
    };
    let root_box = ArcRefCell::new(root_box);
    root_element
        .element_box_slot()
        .set(LayoutBox::BlockLevel(root_box.clone()));
    vec![root_box]
}

impl BoxTree {
    pub fn layout(
        &self,
        layout_context: &LayoutContext,
        viewport: euclid::Size2D<f32, CSSPixel>,
    ) -> FragmentTree {
        let style = ComputedValues::initial_values();

        // FIXME: use the document’s mode:
        // https://drafts.csswg.org/css-writing-modes/#principal-flow
        let physical_containing_block = PhysicalRect::new(
            PhysicalPoint::zero(),
            PhysicalSize::new(Length::new(viewport.width), Length::new(viewport.height)),
        );
        let initial_containing_block = DefiniteContainingBlock {
            size: LogicalVec2 {
                inline: physical_containing_block.size.width,
                block: physical_containing_block.size.height,
            },
            style,
        };

        let mut positioning_context =
            PositioningContext::new_for_containing_block_for_all_descendants();
        let independent_layout = self.root.layout(
            layout_context,
            &mut positioning_context,
            &(&initial_containing_block).into(),
        );

        let mut root_fragments = independent_layout
            .fragments
            .into_iter()
            .map(|fragment| ArcRefCell::new(fragment))
            .collect::<Vec<_>>();

        // Zero box for `:root { display: none }`, one for the root element otherwise.
        assert!(root_fragments.len() <= 1);

        // There may be more fragments at the top-level
        // (for positioned boxes whose containing is the initial containing block)
        // but only if there was one fragment for the root element.
        positioning_context.layout_initial_containing_block_children(
            layout_context,
            &initial_containing_block,
            &mut root_fragments,
        );

        let scrollable_overflow = root_fragments
            .iter()
            .fold(PhysicalRect::zero(), |acc, child| {
                let child_overflow = child
                    .borrow()
                    .scrollable_overflow(&physical_containing_block);

                // https://drafts.csswg.org/css-overflow/#scrolling-direction
                // We want to clip scrollable overflow on box-start and inline-start
                // sides of the scroll container.
                //
                // FIXME(mrobinson, bug 25564): This should take into account writing
                // mode.
                let child_overflow = PhysicalRect::new(
                    euclid::Point2D::zero(),
                    euclid::Size2D::new(
                        child_overflow.size.width + child_overflow.origin.x,
                        child_overflow.size.height + child_overflow.origin.y,
                    ),
                );
                acc.union(&child_overflow)
            });

        FragmentTree {
            root_fragments,
            scrollable_overflow,
            initial_containing_block: physical_containing_block,
            canvas_background: self.canvas_background.clone(),
        }
    }
}

/// https://drafts.csswg.org/css-backgrounds/#root-background
#[derive(Clone, Serialize)]
pub struct CanvasBackground {
    /// DOM node for the root element
    pub root_element: OpaqueNode,

    /// The element whose style the canvas takes background properties from (see next field).
    /// This can be the root element (same as the previous field), or the HTML `<body>` element.
    /// See https://drafts.csswg.org/css-backgrounds/#body-background
    pub from_element: OpaqueNode,

    /// The computed styles to take background properties from.
    #[serde(skip)]
    pub style: Option<Arc<ComputedValues>>,
}

impl CanvasBackground {
    fn for_root_element<'dom>(context: &LayoutContext, root_element: impl NodeExt<'dom>) -> Self {
        let root_style = root_element.style(context);

        let mut style = root_style;
        let mut from_element = root_element;

        // https://drafts.csswg.org/css-backgrounds/#body-background
        // “if the computed value of background-image on the root element is none
        //  and its background-color is transparent”
        if style.background_is_transparent() &&
            // “For documents whose root element is an HTML `HTML` element
            //  or an XHTML `html` element”
            root_element.type_id() == LayoutNodeType::Element(LayoutElementType::HTMLHtmlElement) &&
            // Don’t try to access styles for an unstyled subtree
            !matches!(style.clone_display().into(), Display::None)
        {
            // “that element’s first HTML `BODY` or XHTML `body` child element”
            if let Some(body) = iter_child_nodes(root_element).find(|child| {
                child.is_element() &&
                    child.type_id() ==
                        LayoutNodeType::Element(LayoutElementType::HTMLBodyElement)
            }) {
                style = body.style(context);
                from_element = body;
            }
        }

        Self {
            root_element: root_element.opaque(),
            from_element: from_element.opaque(),

            // “However, if no boxes are generated for the element
            //  whose background would be used for the canvas
            //  (for example, if the root element has display: none),
            //  then the canvas background is transparent.”
            style: if let Display::GeneratingBox(_) = style.clone_display().into() {
                Some(style)
            } else {
                None
            },
        }
    }
}