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layout: Rewrite the block formatting context/float inline-size

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speculation code.

The old code tried to do the speculation as a single bottom-up pass
after intrinsic inline-size calculation, which was unable to handle
cases like this:

    <div>
        <div style="float: left">Foo</div>
    </div>
    <div>
        <div style="overflow: hidden">Bar</div>
    </div>

No single bottom-up pass could possibly handle this case, because the
inline-size of the float flowing out of the "Foo" block could never make
it down to the "Bar" block, where it is needed for speculation.

On the pages I tried, this regresses layout performance by 1%-2%.

I first noticed this breaking some pages, like the Google SERPs, several
months ago.
This commit is contained in:
Patrick Walton 2016-03-18 15:23:08 -07:00
parent 9b2ae3a62f
commit b29719e36b
15 changed files with 346 additions and 184 deletions
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28
components/layout/fragment.rs
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@ -1027,6 +1027,24 @@ impl Fragment {
}
}
/// Returns a guess as to the distances from the margin edge of this fragment to its content
/// in the inline direction. This will generally be correct unless percentages are involved.
///
/// This is used for the float placement speculation logic.
pub fn guess_inline_content_edge_offsets(&self) -> SpeculatedInlineContentEdgeOffsets {
let logical_margin = self.style.logical_margin();
let logical_padding = self.style.logical_padding();
let border_width = self.border_width();
SpeculatedInlineContentEdgeOffsets {
start: MaybeAuto::from_style(logical_margin.inline_start, Au(0)).specified_or_zero() +
model::specified(logical_padding.inline_start, Au(0)) +
border_width.inline_start,
end: MaybeAuto::from_style(logical_margin.inline_end, Au(0)).specified_or_zero() +
model::specified(logical_padding.inline_end, Au(0)) +
border_width.inline_end,
}
}
pub fn calculate_line_height(&self, layout_context: &LayoutContext) -> Au {
let font_style = self.style.get_font_arc();
let font_metrics = text::font_metrics_for_style(&mut layout_context.font_context(), font_style);
@ -2634,3 +2652,13 @@ bitflags! {
const HAS_LAYER = 0x01,
}
}
/// Specified distances from the margin edge of a block to its content in the inline direction.
/// These are returned by `guess_inline_content_edge_offsets()` and are used in the float placement
/// speculation logic.
#[derive(Copy, Clone, Debug)]
pub struct SpeculatedInlineContentEdgeOffsets {
pub start: Au,
pub end: Au,
}