servo/components/layout/taffy/layout.rs
Oriol Brufau 1cceb5f6a0
layout: Inform child layout about final block size (#36980)
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>
2025-05-14 20:35:49 +00:00

639 lines
27 KiB
Rust

/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
use app_units::Au;
use atomic_refcell::{AtomicRef, AtomicRefCell};
use style::Zero;
use style::properties::ComputedValues;
use style::values::specified::align::AlignFlags;
use style::values::specified::box_::DisplayInside;
use taffy::style_helpers::{TaffyMaxContent, TaffyMinContent};
use taffy::{AvailableSpace, MaybeMath, RequestedAxis, RunMode};
use super::{
SpecificTaffyGridInfo, TaffyContainer, TaffyItemBox, TaffyItemBoxInner, TaffyStyloStyle,
};
use crate::cell::ArcRefCell;
use crate::context::LayoutContext;
use crate::formatting_contexts::{
Baselines, IndependentFormattingContext, IndependentFormattingContextContents,
};
use crate::fragment_tree::{
BoxFragment, CollapsedBlockMargins, Fragment, FragmentFlags, SpecificLayoutInfo,
};
use crate::geom::{
LazySize, LogicalVec2, PhysicalPoint, PhysicalRect, PhysicalSides, PhysicalSize, Size,
SizeConstraint, Sizes,
};
use crate::layout_box_base::CacheableLayoutResult;
use crate::positioned::{AbsolutelyPositionedBox, PositioningContext, PositioningContextLength};
use crate::sizing::{ComputeInlineContentSizes, ContentSizes, InlineContentSizesResult};
use crate::style_ext::LayoutStyle;
use crate::{ConstraintSpace, ContainingBlock, ContainingBlockSize};
const DUMMY_NODE_ID: taffy::NodeId = taffy::NodeId::new(u64::MAX);
fn resolve_content_size(constraint: AvailableSpace, content_sizes: ContentSizes) -> f32 {
match constraint {
AvailableSpace::Definite(limit) => {
let min = content_sizes.min_content.to_f32_px();
let max = content_sizes.max_content.to_f32_px();
limit.min(max).max(min)
},
AvailableSpace::MinContent => content_sizes.min_content.to_f32_px(),
AvailableSpace::MaxContent => content_sizes.max_content.to_f32_px(),
}
}
#[inline(always)]
fn with_independant_formatting_context<T>(
item: &mut TaffyItemBoxInner,
cb: impl FnOnce(&IndependentFormattingContext) -> T,
) -> T {
match item {
TaffyItemBoxInner::InFlowBox(context) => cb(context),
TaffyItemBoxInner::OutOfFlowAbsolutelyPositionedBox(abspos_box) => {
cb(&AtomicRefCell::borrow(abspos_box).context)
},
}
}
/// Layout parameters and intermediate results about a taffy container,
/// grouped to avoid passing around many parameters
struct TaffyContainerContext<'a> {
source_child_nodes: &'a [ArcRefCell<TaffyItemBox>],
layout_context: &'a LayoutContext<'a>,
positioning_context: &'a mut PositioningContext,
content_box_size_override: &'a ContainingBlock<'a>,
style: &'a ComputedValues,
specific_layout_info: Option<SpecificLayoutInfo>,
/// Temporary location for children specific info, which will be moved into child fragments
child_specific_layout_infos: Vec<Option<SpecificLayoutInfo>>,
}
struct ChildIter(std::ops::Range<usize>);
impl Iterator for ChildIter {
type Item = taffy::NodeId;
fn next(&mut self) -> Option<Self::Item> {
self.0.next().map(taffy::NodeId::from)
}
}
impl taffy::TraversePartialTree for TaffyContainerContext<'_> {
type ChildIter<'a>
= ChildIter
where
Self: 'a;
fn child_ids(&self, _node_id: taffy::NodeId) -> Self::ChildIter<'_> {
ChildIter(0..self.source_child_nodes.len())
}
fn child_count(&self, _node_id: taffy::NodeId) -> usize {
self.source_child_nodes.len()
}
fn get_child_id(&self, _node_id: taffy::NodeId, index: usize) -> taffy::NodeId {
taffy::NodeId::from(index)
}
}
impl taffy::LayoutPartialTree for TaffyContainerContext<'_> {
type CoreContainerStyle<'a>
= TaffyStyloStyle<&'a ComputedValues>
where
Self: 'a;
fn get_core_container_style(&self, _node_id: taffy::NodeId) -> Self::CoreContainerStyle<'_> {
TaffyStyloStyle(self.style)
}
fn set_unrounded_layout(&mut self, node_id: taffy::NodeId, layout: &taffy::Layout) {
let id = usize::from(node_id);
(*self.source_child_nodes[id]).borrow_mut().taffy_layout = *layout;
}
fn compute_child_layout(
&mut self,
node_id: taffy::NodeId,
inputs: taffy::LayoutInput,
) -> taffy::LayoutOutput {
let mut child = (*self.source_child_nodes[usize::from(node_id)]).borrow_mut();
let child = &mut *child;
fn option_f32_to_size(input: Option<f32>) -> Size<Au> {
match input {
None => Size::Initial,
Some(length) => Size::Numeric(Au::from_f32_px(length)),
}
}
with_independant_formatting_context(
&mut child.taffy_level_box,
|independent_context| -> taffy::LayoutOutput {
// TODO: re-evaluate sizing constraint conversions in light of recent layout changes
let containing_block = &self.content_box_size_override;
let style = independent_context.style();
// Adjust known_dimensions from border box to content box
let pbm = independent_context
.layout_style()
.padding_border_margin(containing_block);
let pb_sum = pbm.padding_border_sums.map(|v| v.to_f32_px());
let margin_sum = pbm.margin.auto_is(Au::zero).sum().map(|v| v.to_f32_px());
let content_box_inset = pb_sum + margin_sum;
let content_box_known_dimensions = taffy::Size {
width: inputs
.known_dimensions
.width
.map(|width| width - pb_sum.inline),
height: inputs
.known_dimensions
.height
.map(|height| height - pb_sum.block),
};
match &independent_context.contents {
IndependentFormattingContextContents::Replaced(replaced) => {
let content_box_size = replaced
.used_size_as_if_inline_element_from_content_box_sizes(
containing_block,
style,
independent_context
.preferred_aspect_ratio(&pbm.padding_border_sums),
LogicalVec2 {
block: &Sizes::new(
option_f32_to_size(content_box_known_dimensions.height),
Size::Initial,
Size::Initial,
),
inline: &Sizes::new(
option_f32_to_size(content_box_known_dimensions.width),
Size::Initial,
Size::Initial,
),
},
Size::FitContent.into(),
pbm.padding_border_sums + pbm.margin.auto_is(Au::zero).sum(),
)
.to_physical_size(self.style.writing_mode);
// Create fragments if the RunMode if PerformLayout
// If the RunMode is ComputeSize then only the returned size will be used
if inputs.run_mode == RunMode::PerformLayout {
child.child_fragments = replaced.make_fragments(
self.layout_context,
style,
content_box_size,
);
}
let computed_size = taffy::Size {
width: inputs.known_dimensions.width.unwrap_or_else(|| {
content_box_size.width.to_f32_px() + pb_sum.inline
}),
height: inputs.known_dimensions.height.unwrap_or_else(|| {
content_box_size.height.to_f32_px() + pb_sum.block
}),
};
let size = inputs.known_dimensions.unwrap_or(computed_size);
taffy::LayoutOutput {
size,
..taffy::LayoutOutput::DEFAULT
}
},
IndependentFormattingContextContents::NonReplaced(non_replaced) => {
// Compute inline size
let inline_size = content_box_known_dimensions.width.unwrap_or_else(|| {
let constraint_space = ConstraintSpace {
// TODO: pass min- and max- size
block_size: SizeConstraint::new(
inputs.parent_size.height.map(Au::from_f32_px),
Au::zero(),
None,
),
writing_mode: self.style.writing_mode,
preferred_aspect_ratio: non_replaced.preferred_aspect_ratio(),
};
let result = independent_context
.inline_content_sizes(self.layout_context, &constraint_space);
let adjusted_available_space = inputs
.available_space
.width
.map_definite_value(|width| width - content_box_inset.inline);
resolve_content_size(adjusted_available_space, result.sizes)
});
// Return early if only inline content sizes are requested
if inputs.run_mode == RunMode::ComputeSize &&
inputs.axis == RequestedAxis::Horizontal
{
return taffy::LayoutOutput::from_outer_size(taffy::Size {
width: inline_size + pb_sum.inline,
// If RequestedAxis is Horizontal then height will be ignored.
height: 0.0,
});
}
let content_box_size_override = ContainingBlock {
size: ContainingBlockSize {
inline: Au::from_f32_px(inline_size),
block: content_box_known_dimensions
.height
.map(Au::from_f32_px)
.map_or_else(SizeConstraint::default, SizeConstraint::Definite),
},
style,
};
let lazy_block_size = match content_box_known_dimensions.height {
// FIXME: use the correct min/max sizes.
None => LazySize::intrinsic(),
Some(height) => Au::from_f32_px(height).into(),
};
child.positioning_context = PositioningContext::default();
let layout = non_replaced.layout_without_caching(
self.layout_context,
&mut child.positioning_context,
&content_box_size_override,
containing_block,
false, /* depends_on_block_constraints */
&lazy_block_size,
);
child.child_fragments = layout.fragments;
self.child_specific_layout_infos[usize::from(node_id)] =
layout.specific_layout_info;
let block_size = lazy_block_size
.resolve(|| layout.content_block_size)
.to_f32_px();
let computed_size = taffy::Size {
width: inline_size + pb_sum.inline,
height: block_size + pb_sum.block,
};
let size = inputs.known_dimensions.unwrap_or(computed_size);
taffy::LayoutOutput {
size,
first_baselines: taffy::Point {
x: None,
y: layout.baselines.first.map(|au| au.to_f32_px()),
},
..taffy::LayoutOutput::DEFAULT
}
},
}
},
)
}
}
impl taffy::LayoutGridContainer for TaffyContainerContext<'_> {
type GridContainerStyle<'a>
= TaffyStyloStyle<&'a ComputedValues>
where
Self: 'a;
type GridItemStyle<'a>
= TaffyStyloStyle<AtomicRef<'a, ComputedValues>>
where
Self: 'a;
fn get_grid_container_style(
&self,
_node_id: taffy::prelude::NodeId,
) -> Self::GridContainerStyle<'_> {
TaffyStyloStyle(self.style)
}
fn get_grid_child_style(
&self,
child_node_id: taffy::prelude::NodeId,
) -> Self::GridItemStyle<'_> {
let id = usize::from(child_node_id);
let child = (*self.source_child_nodes[id]).borrow();
TaffyStyloStyle(AtomicRef::map(child, |c| &*c.style))
}
fn set_detailed_grid_info(
&mut self,
_node_id: taffy::NodeId,
specific_layout_info: taffy::DetailedGridInfo,
) {
self.specific_layout_info = Some(SpecificLayoutInfo::Grid(Box::new(
SpecificTaffyGridInfo::from_detailed_grid_layout(specific_layout_info),
)));
}
}
impl ComputeInlineContentSizes for TaffyContainer {
fn compute_inline_content_sizes(
&self,
layout_context: &LayoutContext,
_constraint_space: &ConstraintSpace,
) -> InlineContentSizesResult {
let style = &self.style;
let max_content_inputs = taffy::LayoutInput {
run_mode: taffy::RunMode::ComputeSize,
sizing_mode: taffy::SizingMode::InherentSize,
axis: taffy::RequestedAxis::Horizontal,
vertical_margins_are_collapsible: taffy::Line::FALSE,
known_dimensions: taffy::Size::NONE,
parent_size: taffy::Size::NONE,
available_space: taffy::Size::MAX_CONTENT,
};
let min_content_inputs = taffy::LayoutInput {
available_space: taffy::Size::MIN_CONTENT,
..max_content_inputs
};
let containing_block = &ContainingBlock {
size: ContainingBlockSize {
inline: Au::zero(),
block: SizeConstraint::default(),
},
style,
};
let mut grid_context = TaffyContainerContext {
layout_context,
positioning_context: &mut PositioningContext::default(),
content_box_size_override: containing_block,
style,
source_child_nodes: &self.children,
specific_layout_info: None,
child_specific_layout_infos: vec![None; self.children.len()],
};
let (max_content_output, min_content_output) = match style.clone_display().inside() {
DisplayInside::Grid => {
let max_content_output = taffy::compute_grid_layout(
&mut grid_context,
DUMMY_NODE_ID,
max_content_inputs,
);
let min_content_output = taffy::compute_grid_layout(
&mut grid_context,
DUMMY_NODE_ID,
min_content_inputs,
);
(max_content_output, min_content_output)
},
_ => panic!("Servo is only configured to use Taffy for CSS Grid layout"),
};
let pb_sums = self
.layout_style()
.padding_border_margin(containing_block)
.padding_border_sums;
InlineContentSizesResult {
sizes: ContentSizes {
max_content: Au::from_f32_px(max_content_output.size.width) - pb_sums.inline,
min_content: Au::from_f32_px(min_content_output.size.width) - pb_sums.inline,
},
// TODO: determine this accurately
//
// "true" is a safe default as it will prevent Servo from performing optimizations based
// on the assumption that the node's size does not depend on block constraints.
depends_on_block_constraints: true,
}
}
}
impl TaffyContainer {
/// <https://drafts.csswg.org/css-grid/#layout-algorithm>
pub(crate) fn layout(
&self,
layout_context: &LayoutContext,
positioning_context: &mut PositioningContext,
content_box_size_override: &ContainingBlock,
containing_block: &ContainingBlock,
) -> CacheableLayoutResult {
let mut container_ctx = TaffyContainerContext {
layout_context,
positioning_context,
content_box_size_override,
style: content_box_size_override.style,
source_child_nodes: &self.children,
specific_layout_info: None,
child_specific_layout_infos: vec![None; self.children.len()],
};
let container_style = &content_box_size_override.style;
let align_items = container_style.clone_align_items();
let justify_items = container_style.clone_justify_items();
let pbm = self.layout_style().padding_border_margin(containing_block);
let known_dimensions = taffy::Size {
width: Some(
(content_box_size_override.size.inline + pbm.padding_border_sums.inline)
.to_f32_px(),
),
height: content_box_size_override
.size
.block
.to_definite()
.map(Au::to_f32_px)
.maybe_add(pbm.padding_border_sums.block.to_f32_px()),
};
let taffy_containing_block = taffy::Size {
width: Some(containing_block.size.inline.to_f32_px()),
height: containing_block.size.block.to_definite().map(Au::to_f32_px),
};
let layout_input = taffy::LayoutInput {
run_mode: taffy::RunMode::PerformLayout,
sizing_mode: taffy::SizingMode::InherentSize,
axis: taffy::RequestedAxis::Vertical,
vertical_margins_are_collapsible: taffy::Line::FALSE,
known_dimensions,
parent_size: taffy_containing_block,
available_space: taffy_containing_block.map(AvailableSpace::from),
};
let output = match container_ctx.style.clone_display().inside() {
DisplayInside::Grid => {
taffy::compute_grid_layout(&mut container_ctx, DUMMY_NODE_ID, layout_input)
},
_ => panic!("Servo is only configured to use Taffy for CSS Grid layout"),
};
// Convert `taffy::Layout` into Servo `Fragment`s
// with container_ctx.child_specific_layout_infos will also moved to the corresponding `Fragment`s
let fragments: Vec<Fragment> = self
.children
.iter()
.map(|child| (**child).borrow_mut())
.enumerate()
.map(|(child_id, mut child)| {
fn rect_to_physical_sides<T>(rect: taffy::Rect<T>) -> PhysicalSides<T> {
PhysicalSides::new(rect.top, rect.right, rect.bottom, rect.left)
}
fn size_and_pos_to_logical_rect<T: Default>(
position: taffy::Point<T>,
size: taffy::Size<T>,
) -> PhysicalRect<T> {
PhysicalRect::new(
PhysicalPoint::new(position.x, position.y),
PhysicalSize::new(size.width, size.height),
)
}
let layout = &child.taffy_layout;
let padding = rect_to_physical_sides(layout.padding.map(Au::from_f32_px));
let border = rect_to_physical_sides(layout.border.map(Au::from_f32_px));
let margin = rect_to_physical_sides(layout.margin.map(Au::from_f32_px));
// Compute content box size and position.
//
// For the x/y position we have to correct for the difference between the
// content box and the border box for both the parent and the child.
let content_size = size_and_pos_to_logical_rect(
taffy::Point {
x: Au::from_f32_px(
layout.location.x + layout.padding.left + layout.border.left,
) - pbm.padding.inline_start -
pbm.border.inline_start,
y: Au::from_f32_px(
layout.location.y + layout.padding.top + layout.border.top,
) - pbm.padding.block_start -
pbm.border.block_start,
},
taffy::Size {
width: layout.size.width -
layout.padding.left -
layout.padding.right -
layout.border.left -
layout.border.right,
height: layout.size.height -
layout.padding.top -
layout.padding.bottom -
layout.border.top -
layout.border.bottom,
}
.map(Au::from_f32_px),
);
let child_specific_layout_info: Option<SpecificLayoutInfo> =
std::mem::take(&mut container_ctx.child_specific_layout_infos[child_id]);
let fragment = match &mut child.taffy_level_box {
TaffyItemBoxInner::InFlowBox(independent_box) => {
let mut fragment_info = independent_box.base_fragment_info();
fragment_info
.flags
.insert(FragmentFlags::IS_FLEX_OR_GRID_ITEM);
let mut box_fragment = BoxFragment::new(
fragment_info,
independent_box.style().clone(),
std::mem::take(&mut child.child_fragments),
content_size,
padding,
border,
margin,
None, /* clearance */
)
.with_baselines(Baselines {
first: output.first_baselines.y.map(Au::from_f32_px),
last: None,
})
.with_specific_layout_info(child_specific_layout_info);
child.positioning_context.layout_collected_children(
container_ctx.layout_context,
&mut box_fragment,
);
child
.positioning_context
.adjust_static_position_of_hoisted_fragments_with_offset(
&box_fragment.content_rect.origin.to_vector(),
PositioningContextLength::zero(),
);
container_ctx
.positioning_context
.append(std::mem::take(&mut child.positioning_context));
Fragment::Box(ArcRefCell::new(box_fragment))
},
TaffyItemBoxInner::OutOfFlowAbsolutelyPositionedBox(abs_pos_box) => {
fn resolve_alignment(value: AlignFlags, auto: AlignFlags) -> AlignFlags {
match value {
AlignFlags::AUTO => auto,
AlignFlags::NORMAL => AlignFlags::STRETCH,
value => value,
}
}
let hoisted_box = AbsolutelyPositionedBox::to_hoisted(
abs_pos_box.clone(),
PhysicalRect::from_size(PhysicalSize::new(
Au::from_f32_px(output.size.width),
Au::from_f32_px(output.size.height),
)),
LogicalVec2 {
inline: resolve_alignment(
child.style.clone_align_self().0.0,
align_items.0,
),
block: resolve_alignment(
child.style.clone_justify_self().0.0,
justify_items.computed.0,
),
},
container_ctx.style.writing_mode,
);
let hoisted_fragment = hoisted_box.fragment.clone();
container_ctx.positioning_context.push(hoisted_box);
Fragment::AbsoluteOrFixedPositioned(hoisted_fragment)
},
};
if let TaffyItemBoxInner::InFlowBox(independent_formatting_context) =
&child.taffy_level_box
{
independent_formatting_context
.base
.set_fragment(fragment.clone());
}
fragment
})
.collect();
CacheableLayoutResult {
fragments,
content_block_size: Au::from_f32_px(output.size.height) - pbm.padding_border_sums.block,
content_inline_size_for_table: None,
baselines: Baselines::default(),
// TODO: determine this accurately
//
// "true" is a safe default as it will prevent Servo from performing optimizations based
// on the assumption that the node's size does not depend on block constraints.
depends_on_block_constraints: true,
specific_layout_info: container_ctx.specific_layout_info,
collapsible_margins_in_children: CollapsedBlockMargins::zero(),
}
}
#[inline]
pub(crate) fn layout_style(&self) -> LayoutStyle {
LayoutStyle::Default(&self.style)
}
}