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layout: Share styles to inline box children via SharedInlineStyles (#36896)

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`TextRun`s use their parent style to render. Previously, these styles
were cloned and stored directly in the box tree `TextRun` and resulting
`TextFragment`s. This presents a problem for incremental layout.
Wrapping the style in another layer of shared ownership and mutability
will allow updating all `TextFragment`s during repaint-only incremental
layout by simply updating the box tree styles of the original text
parents.

This adds a new set of borrows when accessing text styles, but also
makes it so that during box tree block construction
`InlineFormattingContext`s are created lazily and now
`InlineFormattingContextBuilder::finish` consumes the builder, making
the API make a bit more sense. This should also improve performance of
box tree block construction slightly.

Testing: This should not change observable behavior and thus is covered
by existing WPT tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
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Martin Robinson 2025-05-12 11:38:50 +02:00 • committed by GitHub
parent db83601b62
commit a0dd2c1beb
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24 changed files with 369 additions and 187 deletions
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11
components/layout/lib.rs
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@ -38,6 +38,7 @@ pub use flow::BoxTree;
pub use fragment_tree::FragmentTree;
pub use layout_impl::LayoutFactoryImpl;
use malloc_size_of_derive::MallocSizeOf;
use servo_arc::Arc as ServoArc;
use style::logical_geometry::WritingMode;
use style::properties::ComputedValues;
use style::values::computed::TextDecorationLine;
@ -45,6 +46,16 @@ use style::values::computed::TextDecorationLine;
use crate::geom::{LogicalVec2, SizeConstraint};
use crate::style_ext::AspectRatio;
/// At times, a style is "owned" by more than one layout object. For example, text
/// fragments need a handle on their parent inline box's style. In order to make
/// incremental layout easier to implement, another layer of shared ownership is added via
/// [`SharedStyle`]. This allows updating the style in originating layout object and
/// having all "depdendent" objects update automatically.
///
/// Note that this is not a cost-free data structure, so should only be
/// used when necessary.
pub(crate) type SharedStyle = ArcRefCell<ServoArc<ComputedValues>>;
/// Represents the set of constraints that we use when computing the min-content
/// and max-content inline sizes of an element.
pub(crate) struct ConstraintSpace {