servo/components/layout_2020/dom.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 std::marker::PhantomData;
use std::sync::Arc;

use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
use base::id::{BrowsingContextId, PipelineId};
use html5ever::{local_name, namespace_url, ns};
use pixels::Image;
use script_layout_interface::wrapper_traits::{
    LayoutDataTrait, LayoutNode, ThreadSafeLayoutElement, ThreadSafeLayoutNode,
};
use script_layout_interface::{
    HTMLCanvasDataSource, LayoutElementType, LayoutNodeType as ScriptLayoutNodeType,
};
use servo_arc::Arc as ServoArc;
use style::properties::ComputedValues;
use style::selector_parser::PseudoElement;

use crate::cell::ArcRefCell;
use crate::context::LayoutContext;
use crate::flexbox::FlexLevelBox;
use crate::flow::BlockLevelBox;
use crate::flow::inline::InlineItem;
use crate::geom::PhysicalSize;
use crate::replaced::{CanvasInfo, CanvasSource};
use crate::taffy::TaffyItemBox;

/// The data that is stored in each DOM node that is used by layout.
#[derive(Default)]
pub struct InnerDOMLayoutData {
    pub(super) self_box: ArcRefCell<Option<LayoutBox>>,
    pub(super) pseudo_before_box: ArcRefCell<Option<LayoutBox>>,
    pub(super) pseudo_after_box: ArcRefCell<Option<LayoutBox>>,
}

/// A box that is stored in one of the `DOMLayoutData` slots.
pub(super) enum LayoutBox {
    DisplayContents,
    BlockLevel(ArcRefCell<BlockLevelBox>),
    InlineLevel(ArcRefCell<InlineItem>),
    FlexLevel(ArcRefCell<FlexLevelBox>),
    TaffyItemBox(ArcRefCell<TaffyItemBox>),
}

/// A wrapper for [`InnerDOMLayoutData`]. This is necessary to give the entire data
/// structure interior mutability, as we will need to mutate the layout data of
/// non-mutable DOM nodes.
#[derive(Default)]
pub struct DOMLayoutData(AtomicRefCell<InnerDOMLayoutData>);

// The implementation of this trait allows the data to be stored in the DOM.
impl LayoutDataTrait for DOMLayoutData {}

pub struct BoxSlot<'dom> {
    pub(crate) slot: Option<ArcRefCell<Option<LayoutBox>>>,
    pub(crate) marker: PhantomData<&'dom ()>,
}

/// A mutable reference to a `LayoutBox` stored in a DOM element.
impl BoxSlot<'_> {
    pub(crate) fn new(slot: ArcRefCell<Option<LayoutBox>>) -> Self {
        *slot.borrow_mut() = None;
        let slot = Some(slot);
        Self {
            slot,
            marker: PhantomData,
        }
    }

    pub(crate) fn dummy() -> Self {
        let slot = None;
        Self {
            slot,
            marker: PhantomData,
        }
    }

    pub(crate) fn set(mut self, box_: LayoutBox) {
        if let Some(slot) = &mut self.slot {
            *slot.borrow_mut() = Some(box_);
        }
    }
}

impl Drop for BoxSlot<'_> {
    fn drop(&mut self) {
        if !std::thread::panicking() {
            if let Some(slot) = &mut self.slot {
                assert!(slot.borrow().is_some(), "failed to set a layout box");
            }
        }
    }
}

pub(crate) trait NodeExt<'dom>: 'dom + LayoutNode<'dom> {
    /// Returns the image if it’s loaded, and its size in image pixels
    /// adjusted for `image_density`.
    fn as_image(self) -> Option<(Option<Arc<Image>>, PhysicalSize<f64>)>;
    fn as_canvas(self) -> Option<(CanvasInfo, PhysicalSize<f64>)>;
    fn as_iframe(self) -> Option<(PipelineId, BrowsingContextId)>;
    fn as_video(self) -> Option<(Option<webrender_api::ImageKey>, Option<PhysicalSize<f64>>)>;
    fn as_typeless_object_with_data_attribute(self) -> Option<String>;
    fn style(self, context: &LayoutContext) -> ServoArc<ComputedValues>;

    fn layout_data_mut(self) -> AtomicRefMut<'dom, InnerDOMLayoutData>;
    fn layout_data(self) -> Option<AtomicRef<'dom, InnerDOMLayoutData>>;
    fn element_box_slot(&self) -> BoxSlot<'dom>;
    fn pseudo_element_box_slot(&self, which: PseudoElement) -> BoxSlot<'dom>;
    fn unset_pseudo_element_box(self, which: PseudoElement);

    /// Remove boxes for the element itself, and its `:before` and `:after` if any.
    fn unset_all_boxes(self);
}

impl<'dom, LayoutNodeType> NodeExt<'dom> for LayoutNodeType
where
    LayoutNodeType: 'dom + LayoutNode<'dom>,
{
    fn as_image(self) -> Option<(Option<Arc<Image>>, PhysicalSize<f64>)> {
        let node = self.to_threadsafe();
        let (resource, metadata) = node.image_data()?;
        let (width, height) = resource
            .as_ref()
            .map(|image| (image.width, image.height))
            .or_else(|| metadata.map(|metadata| (metadata.width, metadata.height)))
            .unwrap_or((0, 0));
        let (mut width, mut height) = (width as f64, height as f64);
        if let Some(density) = node.image_density().filter(|density| *density != 1.) {
            width /= density;
            height /= density;
        }
        Some((resource, PhysicalSize::new(width, height)))
    }

    fn as_video(self) -> Option<(Option<webrender_api::ImageKey>, Option<PhysicalSize<f64>>)> {
        let node = self.to_threadsafe();
        let data = node.media_data()?;
        let natural_size = if let Some(frame) = data.current_frame {
            Some(PhysicalSize::new(frame.width.into(), frame.height.into()))
        } else {
            data.metadata
                .map(|meta| PhysicalSize::new(meta.width.into(), meta.height.into()))
        };
        Some((
            data.current_frame.map(|frame| frame.image_key),
            natural_size,
        ))
    }

    fn as_canvas(self) -> Option<(CanvasInfo, PhysicalSize<f64>)> {
        let node = self.to_threadsafe();
        let canvas_data = node.canvas_data()?;
        let source = match canvas_data.source {
            HTMLCanvasDataSource::WebGL(texture_id) => CanvasSource::WebGL(texture_id),
            HTMLCanvasDataSource::Image(image_key) => CanvasSource::Image(image_key),
            HTMLCanvasDataSource::WebGPU(image_key) => CanvasSource::WebGPU(image_key),
            HTMLCanvasDataSource::Empty => CanvasSource::Empty,
        };
        Some((
            CanvasInfo { source },
            PhysicalSize::new(canvas_data.width.into(), canvas_data.height.into()),
        ))
    }

    fn as_iframe(self) -> Option<(PipelineId, BrowsingContextId)> {
        let node = self.to_threadsafe();
        match (node.iframe_pipeline_id(), node.iframe_browsing_context_id()) {
            (Some(pipeline_id), Some(browsing_context_id)) => {
                Some((pipeline_id, browsing_context_id))
            },
            _ => None,
        }
    }

    fn as_typeless_object_with_data_attribute(self) -> Option<String> {
        if self.type_id() != ScriptLayoutNodeType::Element(LayoutElementType::HTMLObjectElement) {
            return None;
        }

        // TODO: This is the what the legacy layout system did, but really if Servo
        // supports any `<object>` that's an image, it should support those with URLs
        // and `type` attributes with image mime types.
        let element = self.to_threadsafe().as_element()?;
        if element.get_attr(&ns!(), &local_name!("type")).is_some() {
            return None;
        }
        element
            .get_attr(&ns!(), &local_name!("data"))
            .map(|string| string.to_owned())
    }

    fn style(self, context: &LayoutContext) -> ServoArc<ComputedValues> {
        self.to_threadsafe().style(context.shared_context())
    }

    fn layout_data_mut(self) -> AtomicRefMut<'dom, InnerDOMLayoutData> {
        if LayoutNode::layout_data(&self).is_none() {
            self.initialize_layout_data::<DOMLayoutData>();
        }
        LayoutNode::layout_data(&self)
            .unwrap()
            .downcast_ref::<DOMLayoutData>()
            .unwrap()
            .0
            .borrow_mut()
    }

    fn layout_data(self) -> Option<AtomicRef<'dom, InnerDOMLayoutData>> {
        LayoutNode::layout_data(&self)
            .map(|data| data.downcast_ref::<DOMLayoutData>().unwrap().0.borrow())
    }

    fn element_box_slot(&self) -> BoxSlot<'dom> {
        BoxSlot::new(self.layout_data_mut().self_box.clone())
    }

    fn pseudo_element_box_slot(&self, pseudo_element_type: PseudoElement) -> BoxSlot<'dom> {
        let data = self.layout_data_mut();
        let cell = match pseudo_element_type {
            PseudoElement::Before => &data.pseudo_before_box,
            PseudoElement::After => &data.pseudo_after_box,
            _ => unreachable!(
                "Asked for box slot for unsupported pseudo-element: {:?}",
                pseudo_element_type
            ),
        };
        BoxSlot::new(cell.clone())
    }

    fn unset_pseudo_element_box(self, pseudo_element_type: PseudoElement) {
        let data = self.layout_data_mut();
        let cell = match pseudo_element_type {
            PseudoElement::Before => &data.pseudo_before_box,
            PseudoElement::After => &data.pseudo_after_box,
            _ => unreachable!(
                "Asked for box slot for unsupported pseudo-element: {:?}",
                pseudo_element_type
            ),
        };
        *cell.borrow_mut() = None;
    }

    fn unset_all_boxes(self) {
        let data = self.layout_data_mut();
        *data.self_box.borrow_mut() = None;
        *data.pseudo_before_box.borrow_mut() = None;
        *data.pseudo_after_box.borrow_mut() = None;
        // Stylo already takes care of removing all layout data
        // for DOM descendants of elements with `display: none`.
    }
}