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Correctly paint the CSS canvas’ background

Browse source 
https://drafts.csswg.org/css-backgrounds/#special-backgrounds

Fixes https://github.com/servo/servo/issues/25559
Closes https://github.com/servo/servo/pull/26121, as it is an alternative.
This commit is contained in:
Simon Sapin 2020-05-04 15:50:57 +02:00
parent c7acfc37ed
commit 1f6efbf9e9
9 changed files with 312 additions and 37 deletions
Download patch file Download diff file Expand all files Collapse all files

86
components/layout_2020/flow/root.rs
View file

@ -8,7 +8,7 @@ use crate::display_list::stacking_context::{
ContainingBlock, ContainingBlockInfo, StackingContext, StackingContextBuildMode,
StackingContextBuilder,
};
use crate::dom_traversal::{Contents, NodeExt};
use crate::dom_traversal::{iter_child_nodes, Contents, NodeExt};
use crate::element_data::LayoutBox;
use crate::flow::construct::ContainsFloats;
use crate::flow::float::FloatBox;
@ -21,12 +21,14 @@ use crate::positioned::AbsolutelyPositionedBox;
use crate::positioned::PositioningContext;
use crate::replaced::ReplacedContent;
use crate::sizing::ContentSizesRequest;
use crate::style_ext::ComputedValuesExt;
use crate::style_ext::{Display, DisplayGeneratingBox};
use crate::DefiniteContainingBlock;
use app_units::Au;
use euclid::default::{Point2D, Rect, Size2D};
use gfx_traits::print_tree::PrintTree;
use script_layout_interface::wrapper_traits::LayoutNode;
use script_layout_interface::{LayoutElementType, LayoutNodeType};
use servo_arc::Arc;
use style::dom::OpaqueNode;
use style::properties::ComputedValues;
@ -38,6 +40,9 @@ 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,
}
#[derive(Serialize)]
@ -54,10 +59,14 @@ pub struct FragmentTree {
/// The scrollable overflow rectangle for the entire tree
/// https://drafts.csswg.org/css-overflow/#scrollable
scrollable_overflow: PhysicalRect<Length>,
pub(crate) scrollable_overflow: PhysicalRect<Length>,
/// The containing block used in the layout of this fragment tree.
initial_containing_block: PhysicalRect<Length>,
pub(crate) initial_containing_block: PhysicalRect<Length>,
/// https://drafts.csswg.org/css-backgrounds/#special-backgrounds
#[serde(skip)]
pub(crate) canvas_background: CanvasBackground,
}
impl BoxTree {
@ -75,6 +84,7 @@ impl BoxTree {
contains_floats: contains_floats == ContainsFloats::Yes,
contents: BlockContainer::BlockLevelBoxes(boxes),
},
canvas_background: CanvasBackground::for_root_element(context, root_element),
}
}
}
@ -226,6 +236,7 @@ impl BoxTree {
root_fragments,
scrollable_overflow,
initial_containing_block: physical_containing_block,
canvas_background: self.canvas_background.clone(),
}
}
}
@ -256,6 +267,14 @@ impl FragmentTree {
}
stacking_context.sort();
// Paint the canvas’ background (if any) before/under everything else
stacking_context.build_canvas_background_display_list(
builder,
self,
&self.initial_containing_block,
);
stacking_context.build_display_list(builder);
}
@ -362,3 +381,64 @@ impl FragmentTree {
.unwrap_or_else(Rect::zero)
}
}
/// https://drafts.csswg.org/css-backgrounds/#root-background
#[derive(Clone, Serialize)]
pub(crate) 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
},
}
}
}