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layout: Inform child layout about final block size (#36980)

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Before this patch it wasn't possibly to simultaneously support intrinsic
min/max sizes and content alignment in the block axis. For example,
block containers only support the former, and flex containers only the
latter.

The reason is that the final block size was decided by the parent
formatting context *after* performing layout, while content alignment is
performed *during* layout.

To address the problem, this introduces the struct `LazySize`, which
contains the data to resolve the final size, except for the intrinsic
size. Thus the parent formatting context can first create a `LazySize`,
then pass it to the child layout so that (if necessary) it can compute
the final size once the intrinsic one is known, and after layout the
parent formatting context uses it to actually size the child.

This PR just provides the functionality that will be used by follow-ups,
but at this point no layout is using the `LazySize` provided by the
parent, so there shouldn't be any behavior change yet.

Testing: Unnecessary (no behavior change)
This is part of #36981 and #36982

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
This commit is contained in:
Oriol Brufau 2025-05-14 13:35:49 -07:00 • committed by GitHub
parent 1499e2a874
commit 1cceb5f6a0
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6 changed files with 194 additions and 81 deletions
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61
components/layout/positioned.rs
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@ -24,12 +24,11 @@ use crate::fragment_tree::{
BoxFragment, Fragment, FragmentFlags, HoistedSharedFragment, SpecificLayoutInfo,
};
use crate::geom::{
AuOrAuto, LengthPercentageOrAuto, LogicalRect, LogicalSides, LogicalSides1D, LogicalVec2,
PhysicalPoint, PhysicalRect, PhysicalSides, PhysicalSize, PhysicalVec, Size, Sizes, ToLogical,
ToLogicalWithContainingBlock,
AuOrAuto, LazySize, LengthPercentageOrAuto, LogicalRect, LogicalSides, LogicalSides1D,
LogicalVec2, PhysicalPoint, PhysicalRect, PhysicalSides, PhysicalSize, PhysicalVec, Size,
Sizes, ToLogical, ToLogicalWithContainingBlock,
};
use crate::layout_box_base::LayoutBoxBase;
use crate::sizing::ContentSizes;
use crate::style_ext::{Clamp, ComputedValuesExt, ContentBoxSizesAndPBM, DisplayInside};
use crate::{
ConstraintSpace, ContainingBlock, ContainingBlockSize, DefiniteContainingBlock,
@ -560,18 +559,32 @@ impl HoistedAbsolutelyPositionedBox {
// The block size can depend on layout results, so we only solve it extrinsically,
// we may have to resolve it properly later on.
let extrinsic_block_size = block_axis_solver.solve_size_extrinsically();
let block_automatic_size = block_axis_solver.automatic_size();
let block_stretch_size = Some(block_axis_solver.stretch_size());
let extrinsic_block_size = block_axis_solver.computed_sizes.resolve_extrinsic(
block_automatic_size,
Au::zero(),
block_stretch_size,
);
// The inline axis can be fully resolved, computing intrinsic sizes using the
// extrinsic block size.
let inline_size = inline_axis_solver.solve_size(|| {
let get_inline_content_size = || {
let ratio = context.preferred_aspect_ratio(&pbm.padding_border_sums);
let constraint_space =
ConstraintSpace::new(extrinsic_block_size, style.writing_mode, ratio);
context
.inline_content_sizes(layout_context, &constraint_space)
.sizes
});
};
let inline_size = inline_axis_solver.computed_sizes.resolve(
Direction::Inline,
inline_axis_solver.automatic_size(),
Au::zero,
Some(inline_axis_solver.stretch_size()),
get_inline_content_size,
is_table,
);
let containing_block_for_children = ContainingBlock {
size: ContainingBlockSize {
@ -587,6 +600,14 @@ impl HoistedAbsolutelyPositionedBox {
"Mixed horizontal and vertical writing modes are not supported yet"
);
let lazy_block_size = LazySize::new(
&block_axis_solver.computed_sizes,
Direction::Block,
block_automatic_size,
Au::zero,
block_stretch_size,
is_table,
);
let independent_layout = non_replaced.layout(
layout_context,
&mut positioning_context,
@ -594,6 +615,7 @@ impl HoistedAbsolutelyPositionedBox {
containing_block,
&context.base,
false, /* depends_on_block_constraints */
&lazy_block_size,
);
// Tables can become narrower than predicted due to collapsed columns
@ -602,8 +624,8 @@ impl HoistedAbsolutelyPositionedBox {
.unwrap_or(inline_size);
// Now we can properly solve the block size.
let block_size = block_axis_solver
.solve_size(|| independent_layout.content_block_size.into());
let block_size =
lazy_block_size.resolve(|| independent_layout.content_block_size);
content_size = LogicalVec2 {
inline: inline_size,
@ -765,27 +787,6 @@ impl AbsoluteAxisSolver<'_> {
)
}
#[inline]
fn solve_size_extrinsically(&self) -> SizeConstraint {
self.computed_sizes.resolve_extrinsic(
self.automatic_size(),
Au::zero(),
Some(self.stretch_size()),
)
}
#[inline]
fn solve_size(&self, get_content_size: impl FnOnce() -> ContentSizes) -> Au {
self.computed_sizes.resolve(
self.axis,
self.automatic_size(),
Au::zero,
Some(self.stretch_size()),
get_content_size,
self.is_table,
)
}
fn solve_margins(&self, size: Au) -> LogicalSides1D<Au> {
if self.box_offsets.either_auto() {
LogicalSides1D::new(