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Simplify layout of absolutes with static insets

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Absolutes with static insets need to be laid out at their ancestor
containing blocks, but their position is dependent on their parent's
layout. The static layout position is passed up the tree during hoisting
and ancestors each add their own offset to the position until it is
relative to the containing block that contains the absolute.

This is currently done with a closure and a fairly tricky "tree rank"
numbering system that needs to be threaded through the entire layout.
This change replaces that system.

Every time a child is laid out we create a positioning context to hold
any absolute children (this can be optimized away at a later time). At
each of these moments, we call a method to aggregate offsets to the
static insets of hoisted absolutes. This makes the logic easier to
follow and will also allow implementing this behavior for inline-blocks,
which was impossible with the old system.
This commit is contained in:
Martin Robinson 2023-06-19 18:04:05 +02:00
parent 836ae5fa48
commit 459a7d26aa
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GPG key ID: D56AA4FA55EFE6F8
7 changed files with 174 additions and 235 deletions
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146
components/layout_2020/flexbox/layout.rs
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@ -55,7 +55,6 @@ struct FlexContext<'a> {
/// A flex item with some intermediate results
struct FlexItem<'a> {
box_: &'a mut IndependentFormattingContext,
tree_rank: usize,
content_box_size: FlexRelativeVec2<LengthOrAuto>,
content_min_size: FlexRelativeVec2<Length>,
content_max_size: FlexRelativeVec2<Option<Length>>,
@ -92,7 +91,7 @@ struct FlexItemLayoutResult {
/// Return type of `FlexLine::layout`
struct FlexLineLayoutResult {
cross_size: Length,
item_fragments: Vec<BoxFragment>, // One per flex item, in the given order
item_fragments: Vec<(BoxFragment, PositioningContext)>, // One per flex item, in the given order
}
impl FlexContext<'_> {
@ -150,7 +149,6 @@ impl FlexContainer {
layout_context: &LayoutContext,
positioning_context: &mut PositioningContext,
containing_block: &ContainingBlock,
tree_rank: usize,
) -> IndependentLayout {
// Actual length may be less, but we guess that usually not by a lot
let mut flex_items = Vec::with_capacity(self.children.len());
@ -161,8 +159,7 @@ impl FlexContainer {
let original_order_with_absolutely_positioned = self
.children
.iter()
.enumerate()
.map(|(tree_rank, arcrefcell)| {
.map(|arcrefcell| {
let borrowed = arcrefcell.borrow_mut();
match &*borrowed {
FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(absolutely_positioned) => {
@ -173,56 +170,54 @@ impl FlexContainer {
FlexLevelBox::FlexItem(item) => item,
_ => unreachable!(),
});
flex_items.push((tree_rank, item));
flex_items.push(item);
Err(())
},
}
})
.collect::<Vec<_>>();
let mut content_block_size_option_dance = None;
let fragments =
positioning_context.adjust_static_positions(tree_rank, |positioning_context| {
let (mut flex_item_fragments, content_block_size) = layout(
layout_context,
positioning_context,
containing_block,
flex_items
.iter_mut()
.map(|(tree_rank, child)| (*tree_rank, &mut **child)),
);
content_block_size_option_dance = Some(content_block_size);
let fragments = original_order_with_absolutely_positioned
.into_iter()
.enumerate()
.map(|(tree_rank, child_as_abspos)| match child_as_abspos {
Err(()) => {
// The `()` here is a place-holder for a flex item.
// The `flex_item_fragments` iterator yields one fragment
// per flex item, in the original order.
Fragment::Box(flex_item_fragments.next().unwrap())
},
Ok(absolutely_positioned) => {
let hoisted_box = AbsolutelyPositionedBox::to_hoisted(
absolutely_positioned,
Vec2::zero(),
tree_rank,
containing_block,
);
let hoisted_fragment = hoisted_box.fragment.clone();
positioning_context.push(hoisted_box);
Fragment::AbsoluteOrFixedPositioned(hoisted_fragment)
},
})
.collect::<Vec<_>>();
// There should be no more flex items
assert!(flex_item_fragments.next().is_none());
fragments
});
let (mut flex_item_fragments, content_block_size) = layout(
layout_context,
positioning_context,
containing_block,
flex_items.iter_mut().map(|child| &mut **child),
);
let fragments = original_order_with_absolutely_positioned
.into_iter()
.map(|child_as_abspos| match child_as_abspos {
Err(()) => {
// The `()` here is a place-holder for a flex item.
// The `flex_item_fragments` iterator yields one fragment
// per flex item, in the original order.
let (fragment, mut child_positioning_context) =
flex_item_fragments.next().unwrap();
let fragment = Fragment::Box(fragment);
child_positioning_context
.adjust_static_position_of_hoisted_fragments(&fragment);
positioning_context.append(child_positioning_context);
fragment
},
Ok(absolutely_positioned) => {
let hoisted_box = AbsolutelyPositionedBox::to_hoisted(
absolutely_positioned,
Vec2::zero(),
containing_block,
);
let hoisted_fragment = hoisted_box.fragment.clone();
positioning_context.push(hoisted_box);
Fragment::AbsoluteOrFixedPositioned(hoisted_fragment)
},
})
.collect::<Vec<_>>();
// There should be no more flex items
assert!(flex_item_fragments.next().is_none());
IndependentLayout {
fragments,
content_block_size: content_block_size_option_dance.unwrap(),
content_block_size,
}
}
}
@ -232,8 +227,11 @@ fn layout<'context, 'boxes>(
layout_context: &LayoutContext,
positioning_context: &mut PositioningContext,
containing_block: &ContainingBlock,
flex_item_boxes: impl Iterator<Item = (usize, &'boxes mut IndependentFormattingContext)>,
) -> (impl Iterator<Item = BoxFragment>, Length) {
flex_item_boxes: impl Iterator<Item = &'boxes mut IndependentFormattingContext>,
) -> (
impl Iterator<Item = (BoxFragment, PositioningContext)>,
Length,
) {
// FIXME: get actual min/max cross size for the flex container.
// We have access to style for the flex container in `containing_block.style`,
// but resolving percentages there requires access
@ -290,7 +288,7 @@ fn layout<'context, 'boxes>(
};
let mut flex_items = flex_item_boxes
.map(|(tree_rank, box_)| FlexItem::new(&flex_context, box_, tree_rank))
.map(|box_| FlexItem::new(&flex_context, box_))
.collect::<Vec<_>>();
// “Determine the main size of the flex container”
@ -387,7 +385,7 @@ fn layout<'context, 'boxes>(
container_main_size
},
};
let fragments = flex_lines
let fragments_and_positioning_contexts = flex_lines
.into_iter()
.zip(line_cross_start_positions)
.flat_map(move |(mut line, line_cross_start_position)| {
@ -409,21 +407,17 @@ fn layout<'context, 'boxes>(
inline: container_cross_size - line_cross_start_position - line.cross_size,
},
};
for fragment in &mut line.item_fragments {
for (fragment, _) in &mut line.item_fragments {
fragment.content_rect.start_corner += &flow_relative_line_position
}
line.item_fragments
})
.into_iter();
(fragments, content_block_size)
(fragments_and_positioning_contexts, content_block_size)
}
impl<'a> FlexItem<'a> {
fn new(
flex_context: &FlexContext,
box_: &'a mut IndependentFormattingContext,
tree_rank: usize,
) -> Self {
fn new(flex_context: &FlexContext, box_: &'a mut IndependentFormattingContext) -> Self {
let containing_block = flex_context.containing_block;
let box_style = box_.style();
@ -543,7 +537,6 @@ impl<'a> FlexItem<'a> {
Self {
box_,
tree_rank,
content_box_size,
content_min_size,
content_max_size,
@ -730,7 +723,7 @@ impl FlexLine<'_> {
// Determine the used cross size of each flex item
// https://drafts.csswg.org/css-flexbox/#algo-stretch
let (item_used_cross_sizes, item_fragments): (Vec<_>, Vec<_>) = self
let (item_used_cross_sizes, item_results): (Vec<_>, Vec<_>) = self
.items
.iter_mut()
.zip(item_layout_results)
@ -754,10 +747,7 @@ impl FlexLine<'_> {
// so that percentage-sized children can be resolved.”
item_result = item.layout(used_main_size, flex_context, Some(cross_size));
}
flex_context
.positioning_context
.append(item_result.positioning_context);
(cross_size, item_result.fragments)
(cross_size, item_result)
})
.unzip();
@ -838,7 +828,7 @@ impl FlexLine<'_> {
let item_fragments = self
.items
.iter()
.zip(item_fragments)
.zip(item_results)
.zip(
item_used_main_sizes
.iter()
@ -852,20 +842,23 @@ impl FlexLine<'_> {
.map(|(size, start_corner)| FlexRelativeRect { size, start_corner }),
)
.zip(&item_margins)
.map(|(((item, fragments), content_rect), margin)| {
.map(|(((item, item_result), content_rect), margin)| {
let content_rect = flex_context.rect_to_flow_relative(line_size, content_rect);
let margin = flex_context.sides_to_flow_relative(*margin);
let collapsed_margin = CollapsedBlockMargins::from_margin(&margin);
BoxFragment::new(
item.box_.base_fragment_info(),
item.box_.style().clone(),
fragments,
content_rect,
flex_context.sides_to_flow_relative(item.padding),
flex_context.sides_to_flow_relative(item.border),
margin,
Length::zero(),
collapsed_margin,
(
BoxFragment::new(
item.box_.base_fragment_info(),
item.box_.style().clone(),
item_result.fragments,
content_rect,
flex_context.sides_to_flow_relative(item.padding),
flex_context.sides_to_flow_relative(item.border),
margin,
Length::zero(),
collapsed_margin,
),
item_result.positioning_context,
)
})
.collect();
@ -1048,7 +1041,7 @@ impl<'a> FlexItem<'a> {
flex_context: &mut FlexContext,
used_cross_size_override: Option<Length>,
) -> FlexItemLayoutResult {
let mut positioning_context = PositioningContext::new_for_rayon(
let mut positioning_context = PositioningContext::new_for_subtree(
flex_context
.positioning_context
.collects_for_nearest_positioned_ancestor(),
@ -1109,7 +1102,6 @@ impl<'a> FlexItem<'a> {
flex_context.layout_context,
&mut positioning_context,
&item_as_containing_block,
self.tree_rank,
);
let hypothetical_cross_size = self