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layout.rs
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layout.rs
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/* 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 std::cell::Cell;
use app_units::Au;
use atomic_refcell::AtomicRefMut;
use style::properties::longhands::align_content::computed_value::T as AlignContent;
use style::properties::longhands::align_items::computed_value::T as AlignItems;
use style::properties::longhands::align_self::computed_value::T as AlignSelf;
use style::properties::longhands::box_sizing::computed_value::T as BoxSizing;
use style::properties::longhands::flex_direction::computed_value::T as FlexDirection;
use style::properties::longhands::flex_wrap::computed_value::T as FlexWrap;
use style::properties::longhands::justify_content::computed_value::T as JustifyContent;
use style::values::computed::length::Size;
use style::values::computed::Length;
use style::values::generics::flex::GenericFlexBasis as FlexBasis;
use style::values::CSSFloat;
use style::Zero;
use super::geom::{
FlexAxis, FlexRelativeRect, FlexRelativeSides, FlexRelativeVec2, MainStartCrossStart,
};
use super::{FlexContainer, FlexLevelBox};
use crate::cell::ArcRefCell;
use crate::context::LayoutContext;
use crate::formatting_contexts::{Baselines, IndependentFormattingContext, IndependentLayout};
use crate::fragment_tree::{BoxFragment, CollapsedBlockMargins, Fragment};
use crate::geom::{AuOrAuto, LengthOrAuto, LogicalRect, LogicalSides, LogicalVec2};
use crate::positioned::{AbsolutelyPositionedBox, PositioningContext, PositioningContextLength};
use crate::sizing::ContentSizes;
use crate::style_ext::{Clamp, ComputedValuesExt};
use crate::ContainingBlock;
// FIMXE: “Flex items […] `z-index` values other than `auto` create a stacking context
// even if `position` is `static` (behaving exactly as if `position` were `relative`).”
// https://drafts.csswg.org/css-flexbox/#painting
// (likely in `display_list/stacking_context.rs`)
/// Layout parameters and intermediate results about a flex container,
/// grouped to avoid passing around many parameters
struct FlexContext<'a> {
layout_context: &'a LayoutContext<'a>,
positioning_context: &'a mut PositioningContext,
containing_block: &'a ContainingBlock<'a>, // For items
container_is_single_line: bool,
container_min_cross_size: Length,
container_max_cross_size: Option<Length>,
flex_axis: FlexAxis,
main_start_cross_start_sides_are: MainStartCrossStart,
container_definite_inner_size: FlexRelativeVec2<Option<Length>>,
align_content: AlignContent,
align_items: AlignItems,
justify_content: JustifyContent,
}
/// A flex item with some intermediate results
struct FlexItem<'a> {
box_: &'a mut IndependentFormattingContext,
content_box_size: FlexRelativeVec2<LengthOrAuto>,
content_min_size: FlexRelativeVec2<Length>,
content_max_size: FlexRelativeVec2<Option<Length>>,
padding: FlexRelativeSides<Au>,
border: FlexRelativeSides<Au>,
margin: FlexRelativeSides<AuOrAuto>,
/// Sum of padding, border, and margin (with `auto` assumed to be zero) in each axis.
/// This is the difference between an outer and inner size.
pbm_auto_is_zero: FlexRelativeVec2<Au>,
/// <https://drafts.csswg.org/css-flexbox/#algo-main-item>
flex_base_size: Length,
/// <https://drafts.csswg.org/css-flexbox/#algo-main-item>
hypothetical_main_size: Length,
/// This is `align-self`, defaulting to `align-items` if `auto`
align_self: AlignItems,
}
/// Child of a FlexContainer. Can either be absolutely positioned, or not. If not,
/// a placeholder is used and flex content is stored outside of this enum.
enum FlexContent {
AbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
FlexItemPlaceholder,
}
/// A flex line with some intermediate results
struct FlexLine<'a> {
items: &'a mut [FlexItem<'a>],
outer_hypothetical_main_sizes_sum: Length,
}
/// Return type of `FlexItem::layout`
struct FlexItemLayoutResult {
hypothetical_cross_size: Length,
fragments: Vec<Fragment>,
positioning_context: PositioningContext,
}
/// Return type of `FlexLine::layout`
struct FlexLineLayoutResult {
cross_size: Length,
item_fragments: Vec<(BoxFragment, PositioningContext)>, // One per flex item, in the given order
}
impl FlexContext<'_> {
fn vec2_to_flex_relative<T>(&self, x: LogicalVec2<T>) -> FlexRelativeVec2<T> {
self.flex_axis.vec2_to_flex_relative(x)
}
fn sides_to_flex_relative<T>(&self, x: LogicalSides<T>) -> FlexRelativeSides<T> {
self.main_start_cross_start_sides_are
.sides_to_flex_relative(x)
}
fn sides_to_flow_relative<T>(&self, x: FlexRelativeSides<T>) -> LogicalSides<T> {
self.main_start_cross_start_sides_are
.sides_to_flow_relative(x)
}
fn rect_to_flow_relative(
&self,
base_rect_size: FlexRelativeVec2<Length>,
rect: FlexRelativeRect<Length>,
) -> LogicalRect<Length> {
super::geom::rect_to_flow_relative(
self.flex_axis,
self.main_start_cross_start_sides_are,
base_rect_size,
rect,
)
}
fn align_for(&self, align_self: &AlignSelf) -> AlignItems {
match align_self {
AlignSelf::Auto => self.align_items,
AlignSelf::Stretch => AlignItems::Stretch,
AlignSelf::FlexStart => AlignItems::FlexStart,
AlignSelf::FlexEnd => AlignItems::FlexEnd,
AlignSelf::Center => AlignItems::Center,
AlignSelf::Baseline => AlignItems::Baseline,
}
}
}
impl FlexContainer {
pub fn inline_content_sizes(&self) -> ContentSizes {
// FIXME: implement this. The spec for it is the same as for "normal" layout:
// https://drafts.csswg.org/css-flexbox/#layout-algorithm
// … except that the parts that say “the flex container is being sized
// under a min or max-content constraint” apply.
ContentSizes::zero() // Return an incorrect result rather than panic
}
/// <https://drafts.csswg.org/css-flexbox/#layout-algorithm>
pub(crate) fn layout(
&self,
layout_context: &LayoutContext,
positioning_context: &mut PositioningContext,
containing_block: &ContainingBlock,
) -> 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());
// Absolutely-positioned children of the flex container may be interleaved
// with flex items. We need to preserve their relative order for correct painting order,
// which is the order of `Fragment`s in this function’s return value.
//
// Example:
// absolutely_positioned_items_with_original_order = [Some(item), Some(item), None, Some(item), None]
// flex_items = [item, item]
let absolutely_positioned_items_with_original_order = self
.children
.iter()
.map(|arcrefcell| {
let borrowed = arcrefcell.borrow_mut();
match &*borrowed {
FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(absolutely_positioned) => {
FlexContent::AbsolutelyPositionedBox(absolutely_positioned.clone())
},
FlexLevelBox::FlexItem(_) => {
let item = AtomicRefMut::map(borrowed, |child| match child {
FlexLevelBox::FlexItem(item) => item,
_ => unreachable!(),
});
flex_items.push(item);
FlexContent::FlexItemPlaceholder
},
}
})
.collect::<Vec<_>>();
let flex_item_boxes = flex_items.iter_mut().map(|child| &mut **child);
// 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
// to the flex container’s own containing block which we don’t have.
// For now, use incorrect values instead of panicking:
let container_min_cross_size = Length::zero();
let container_max_cross_size = None;
let flex_container_position_style = containing_block.style.get_position();
let flex_wrap = flex_container_position_style.flex_wrap;
let flex_direction = flex_container_position_style.flex_direction;
// Column flex containers are not fully implemented yet,
// so give a different layout instead of panicking.
// FIXME: implement `todo!`s for FlexAxis::Column below, and remove this
let flex_direction = match flex_direction {
FlexDirection::Row | FlexDirection::Column => FlexDirection::Row,
FlexDirection::RowReverse | FlexDirection::ColumnReverse => FlexDirection::RowReverse,
};
let container_is_single_line = match containing_block.style.get_position().flex_wrap {
FlexWrap::Nowrap => true,
FlexWrap::Wrap | FlexWrap::WrapReverse => false,
};
let flex_axis = FlexAxis::from(flex_direction);
let flex_wrap_reverse = match flex_wrap {
FlexWrap::Nowrap | FlexWrap::Wrap => false,
FlexWrap::WrapReverse => true,
};
let align_content = containing_block.style.clone_align_content();
let align_items = containing_block.style.clone_align_items();
let justify_content = containing_block.style.clone_justify_content();
let mut flex_context = FlexContext {
layout_context,
positioning_context,
containing_block,
container_min_cross_size,
container_max_cross_size,
container_is_single_line,
flex_axis,
align_content,
align_items,
justify_content,
main_start_cross_start_sides_are: MainStartCrossStart::from(
flex_direction,
flex_wrap_reverse,
),
// https://drafts.csswg.org/css-flexbox/#definite-sizes
container_definite_inner_size: flex_axis.vec2_to_flex_relative(LogicalVec2 {
inline: Some(containing_block.inline_size.into()),
block: containing_block.block_size.non_auto().map(|t| t.into()),
}),
};
let mut flex_items = flex_item_boxes
.map(|box_| FlexItem::new(&flex_context, box_))
.collect::<Vec<_>>();
// “Determine the main size of the flex container”
// https://drafts.csswg.org/css-flexbox/#algo-main-container
let container_main_size = match flex_axis {
FlexAxis::Row => containing_block.inline_size,
FlexAxis::Column => {
// FIXME “using the rules of the formatting context in which it participates”
// but if block-level with `block-size: max-auto` that requires
// layout of the content to be fully done:
// https://github.com/w3c/csswg-drafts/issues/4905
// Gecko reportedly uses `block-size: fit-content` in this case
// (which requires running another pass of the "full" layout algorithm)
todo!()
// Note: this panic shouldn’t happen since the start of `FlexContainer::layout`
// forces `FlexAxis::Row`.
},
};
// “Resolve the flexible lengths of all the flex items to find their *used main size*.”
// https://drafts.csswg.org/css-flexbox/#algo-flex
let flex_lines = collect_flex_lines(
&mut flex_context,
container_main_size.into(),
&mut flex_items,
|flex_context, mut line| line.layout(flex_context, container_main_size.into()),
);
let content_cross_size = flex_lines
.iter()
.map(|line| line.cross_size)
.sum::<Length>();
// https://drafts.csswg.org/css-flexbox/#algo-cross-container
let container_cross_size = flex_context
.container_definite_inner_size
.cross
.unwrap_or(content_cross_size)
.clamp_between_extremums(
flex_context.container_min_cross_size,
flex_context.container_max_cross_size,
);
// https://drafts.csswg.org/css-flexbox/#algo-line-align
// Align all flex lines per `align-content`.
let line_count = flex_lines.len();
let mut cross_start_position_cursor = Length::zero();
let line_interval = match flex_context.container_definite_inner_size.cross {
Some(cross_size) if line_count >= 2 => {
let free_space = cross_size - content_cross_size;
cross_start_position_cursor = match flex_context.align_content {
AlignContent::Center => free_space / 2.0,
AlignContent::SpaceAround => free_space / (line_count * 2) as CSSFloat,
AlignContent::FlexEnd => free_space,
_ => Length::zero(),
};
match flex_context.align_content {
AlignContent::SpaceBetween => free_space / (line_count - 1) as CSSFloat,
AlignContent::SpaceAround => free_space / line_count as CSSFloat,
_ => Length::zero(),
}
},
_ => Length::zero(),
};
let line_cross_start_positions = flex_lines
.iter()
.map(|line| {
let cross_start = cross_start_position_cursor;
let cross_end = cross_start + line.cross_size + line_interval;
cross_start_position_cursor = cross_end;
cross_start
})
.collect::<Vec<_>>();
let content_block_size = match flex_context.flex_axis {
FlexAxis::Row => {
// `container_main_size` ends up unused here but in this case that’s fine
// since it was already exactly the one decided by the outer formatting context.
container_cross_size
},
FlexAxis::Column => {
// FIXME: `container_cross_size` ends up unused here, which is a bug.
// It is meant to be the used inline-size, but the parent formatting context
// has already decided a possibly-different used inline-size.
// The spec is missing something to resolve this conflict:
// https://github.com/w3c/csswg-drafts/issues/5190
// And we’ll need to change the signature of `IndependentFormattingContext::layout`
// to allow the inner formatting context to “negotiate” a used inline-size
// with the outer one somehow.
container_main_size.into()
},
};
let mut flex_item_fragments = flex_lines
.into_iter()
.zip(line_cross_start_positions)
.flat_map(move |(mut line, line_cross_start_position)| {
let flow_relative_line_position = match (flex_axis, flex_wrap_reverse) {
(FlexAxis::Row, false) => LogicalVec2 {
block: line_cross_start_position,
inline: Length::zero(),
},
(FlexAxis::Row, true) => LogicalVec2 {
block: container_cross_size - line_cross_start_position - line.cross_size,
inline: Length::zero(),
},
(FlexAxis::Column, false) => LogicalVec2 {
block: Length::zero(),
inline: line_cross_start_position,
},
(FlexAxis::Column, true) => LogicalVec2 {
block: Length::zero(),
inline: container_cross_size - line_cross_start_position - line.cross_size,
},
};
for (fragment, _) in &mut line.item_fragments {
fragment.content_rect.start_corner += &flow_relative_line_position
}
line.item_fragments
});
let fragments = absolutely_positioned_items_with_original_order
.into_iter()
.map(|child_as_abspos| match child_as_abspos {
FlexContent::AbsolutelyPositionedBox(absolutely_positioned) => {
let hoisted_box = AbsolutelyPositionedBox::to_hoisted(
absolutely_positioned,
LogicalVec2::zero(),
containing_block,
);
let hoisted_fragment = hoisted_box.fragment.clone();
positioning_context.push(hoisted_box);
Fragment::AbsoluteOrFixedPositioned(hoisted_fragment)
},
FlexContent::FlexItemPlaceholder => {
// 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,
PositioningContextLength::zero(),
);
positioning_context.append(child_positioning_context);
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.into(),
content_inline_size_for_table: None,
baselines: Baselines::default(),
}
}
}
impl<'a> FlexItem<'a> {
fn new(flex_context: &FlexContext, box_: &'a mut IndependentFormattingContext) -> Self {
let containing_block = flex_context.containing_block;
// https://drafts.csswg.org/css-writing-modes/#orthogonal-flows
assert_eq!(
containing_block.style.writing_mode,
box_.style().writing_mode,
"Mixed writing modes are not supported yet"
);
let container_is_horizontal = containing_block.style.writing_mode.is_horizontal();
let item_is_horizontal = box_.style().writing_mode.is_horizontal();
let item_is_orthogonal = item_is_horizontal != container_is_horizontal;
let container_is_row = flex_context.flex_axis == FlexAxis::Row;
let cross_axis_is_item_block_axis = container_is_row ^ item_is_orthogonal;
let pbm = box_.style().padding_border_margin(containing_block);
let content_box_size = box_.style().content_box_size(containing_block, &pbm);
let max_size = box_.style().content_max_box_size(containing_block, &pbm);
let min_size = box_.style().content_min_box_size(containing_block, &pbm);
// https://drafts.csswg.org/css-flexbox/#min-size-auto
let automatic_min_size = || {
// FIXME(stshine): Consider more situations when auto min size is not needed.
if box_.style().get_box().overflow_x.is_scrollable() {
return Length::zero();
}
if cross_axis_is_item_block_axis {
let specified_size_suggestion = content_box_size.inline;
let transferred_size_suggestion = match box_ {
IndependentFormattingContext::NonReplaced(_) => None,
IndependentFormattingContext::Replaced(ref bfc) => {
match (
bfc.contents
.inline_size_over_block_size_intrinsic_ratio(box_.style()),
content_box_size.block,
) {
(Some(ratio), LengthOrAuto::LengthPercentage(block_size)) => {
let block_size = block_size.clamp_between_extremums(
min_size.block.auto_is(Length::zero),
max_size.block,
);
Some(block_size * ratio)
},
_ => None,
}
},
};
let inline_content_size = box_
.inline_content_sizes(flex_context.layout_context)
.min_content;
let content_size_suggestion = match box_ {
IndependentFormattingContext::NonReplaced(_) => inline_content_size,
IndependentFormattingContext::Replaced(ref replaced) => {
if let Some(ratio) = replaced
.contents
.inline_size_over_block_size_intrinsic_ratio(box_.style())
{
inline_content_size.clamp_between_extremums(
(min_size.block.auto_is(Length::zero) * ratio).into(),
max_size.block.map(|l| (l * ratio).into()),
)
} else {
inline_content_size
}
},
};
let result = match specified_size_suggestion {
LengthOrAuto::LengthPercentage(l) => l.min(content_size_suggestion.into()),
LengthOrAuto::Auto => {
if let Some(l) = transferred_size_suggestion {
l.min(content_size_suggestion.into())
} else {
content_size_suggestion.into()
}
},
};
result.clamp_below_max(max_size.inline)
} else {
// FIXME(stshine): Implement this when main axis is item's block axis.
Length::zero()
}
};
let min_size = LogicalVec2 {
inline: min_size.inline.auto_is(automatic_min_size),
block: min_size.block.auto_is(Length::zero),
};
let margin_auto_is_zero = pbm.margin.auto_is(Au::zero);
let content_box_size = flex_context.vec2_to_flex_relative(content_box_size);
let content_max_size = flex_context.vec2_to_flex_relative(max_size);
let content_min_size = flex_context.vec2_to_flex_relative(min_size);
let margin_auto_is_zero = flex_context.sides_to_flex_relative(margin_auto_is_zero);
let padding = flex_context.sides_to_flex_relative(pbm.padding);
let border = flex_context.sides_to_flex_relative(pbm.border);
let padding_border = padding.sum_by_axis() + border.sum_by_axis();
let pbm_auto_is_zero = FlexRelativeVec2 {
main: padding_border.main,
cross: padding_border.cross,
} + margin_auto_is_zero.sum_by_axis();
let align_self = flex_context.align_for(&box_.style().clone_align_self());
let flex_base_size = flex_base_size(
flex_context,
box_,
cross_axis_is_item_block_axis,
content_box_size,
padding_border,
);
let hypothetical_main_size =
flex_base_size.clamp_between_extremums(content_min_size.main, content_max_size.main);
let margin: FlexRelativeSides<AuOrAuto> = flex_context.sides_to_flex_relative(pbm.margin);
Self {
box_,
content_box_size,
content_min_size,
content_max_size,
padding,
border,
margin,
pbm_auto_is_zero,
flex_base_size,
hypothetical_main_size,
align_self,
}
}
}
/// <https://drafts.csswg.org/css-flexbox/#algo-main-item>
fn flex_base_size(
flex_context: &FlexContext,
flex_item: &mut IndependentFormattingContext,
cross_axis_is_item_block_axis: bool,
content_box_size: FlexRelativeVec2<LengthOrAuto>,
padding_border_sums: FlexRelativeVec2<Au>,
) -> Length {
let used_flex_basis = match &flex_item.style().get_position().flex_basis {
FlexBasis::Content => FlexBasis::Content,
FlexBasis::Size(Size::LengthPercentage(length_percentage)) => {
let apply_box_sizing = |length: Length| {
match flex_item.style().get_position().box_sizing {
BoxSizing::ContentBox => length,
BoxSizing::BorderBox => {
// This may make `length` negative,
// but it will be clamped in the hypothetical main size
length - padding_border_sums.main.into()
},
}
};
// “For example, percentage values of flex-basis are resolved
// against the flex item’s containing block (i.e. its flex container);”
match flex_context.container_definite_inner_size.main {
Some(container_definite_main_size) => {
let length = length_percentage
.0
.percentage_relative_to(container_definite_main_size);
FlexBasis::Size(apply_box_sizing(length))
},
None => {
if let Some(length) = length_percentage.0.to_length() {
FlexBasis::Size(apply_box_sizing(length))
} else {
// “and if that containing block’s size is indefinite,
// the used value for `flex-basis` is `content`.”
// https://drafts.csswg.org/css-flexbox/#flex-basis-property
FlexBasis::Content
}
},
}
},
FlexBasis::Size(Size::Auto) => {
// “When specified on a flex item, the `auto` keyword retrieves
// the value of the main size property as the used `flex-basis`.”
match content_box_size.main {
LengthOrAuto::LengthPercentage(length) => FlexBasis::Size(length),
// “If that value is itself `auto`, then the used value is `content`.”
LengthOrAuto::Auto => FlexBasis::Content,
}
},
};
// NOTE: at this point the flex basis is either `content` or a definite length.
// However when we add support for additional values for `width` and `height`
// from https://drafts.csswg.org/css-sizing/#preferred-size-properties,
// it could have those values too.
match used_flex_basis {
FlexBasis::Size(length) => {
// Case A: definite flex basis
length
},
FlexBasis::Content => {
// FIXME: implement cases B, C, D.
// Case E: everything else
// “treating a value of content as max-content.”
if cross_axis_is_item_block_axis {
// The main axis is the inline axis
flex_item
.inline_content_sizes(flex_context.layout_context)
.max_content
.into()
} else {
// FIXME: block-axis content sizing requires another pass
// of "full" layout
todo!()
// Note: this panic shouldn’t happen since the start of `FlexContainer::layout`
// forces `FlexAxis::Row` and the `writing-mode` property is disabled.
}
},
}
}
// “Collect flex items into flex lines”
// https://drafts.csswg.org/css-flexbox/#algo-line-break
fn collect_flex_lines<'items, LineResult>(
flex_context: &mut FlexContext,
container_main_size: Length,
mut items: &'items mut [FlexItem<'items>],
mut each: impl FnMut(&mut FlexContext, FlexLine<'items>) -> LineResult,
) -> Vec<LineResult> {
if flex_context.container_is_single_line {
let line = FlexLine {
outer_hypothetical_main_sizes_sum: items
.iter()
.map(|item| item.hypothetical_main_size + item.pbm_auto_is_zero.main.into())
.sum(),
items,
};
vec![each(flex_context, line)]
} else {
let mut lines = Vec::new();
let mut line_size_so_far = Length::zero();
let mut line_so_far_is_empty = true;
let mut index = 0;
while let Some(item) = items.get(index) {
let item_size = item.hypothetical_main_size + item.pbm_auto_is_zero.main.into();
let line_size_would_be = line_size_so_far + item_size;
let item_fits = line_size_would_be <= container_main_size;
if item_fits || line_so_far_is_empty {
line_size_so_far = line_size_would_be;
line_so_far_is_empty = false;
index += 1;
} else {
// We found something that doesn’t fit. This line ends *before* this item.
let (line_items, rest) = items.split_at_mut(index);
let line = FlexLine {
items: line_items,
outer_hypothetical_main_sizes_sum: line_size_so_far,
};
items = rest;
lines.push(each(flex_context, line));
// The next line has this item.
line_size_so_far = item_size;
index = 1;
}
}
// The last line is added even without finding an item that doesn’t fit
let line = FlexLine {
items,
outer_hypothetical_main_sizes_sum: line_size_so_far,
};
lines.push(each(flex_context, line));
lines
}
}
impl FlexLine<'_> {
fn layout(
&mut self,
flex_context: &mut FlexContext,
container_main_size: Length,
) -> FlexLineLayoutResult {
let (item_used_main_sizes, remaining_free_space) =
self.resolve_flexible_lengths(container_main_size);
// https://drafts.csswg.org/css-flexbox/#algo-cross-item
let item_layout_results = self
.items
.iter_mut()
.zip(&item_used_main_sizes)
.map(|(item, &used_main_size)| item.layout(used_main_size, flex_context, None))
.collect::<Vec<_>>();
// https://drafts.csswg.org/css-flexbox/#algo-cross-line
let line_cross_size = self.cross_size(&item_layout_results, flex_context);
let line_size = FlexRelativeVec2 {
main: container_main_size,
cross: line_cross_size,
};
// FIXME: Handle `align-content: stretch`
// https://drafts.csswg.org/css-flexbox/#algo-line-stretch
// FIXME: Collapse `visibility: collapse` items
// This involves “restart layout from the beginning” with a modified second round,
// which will make structuring the code… interesting.
// https://drafts.csswg.org/css-flexbox/#algo-visibility
// Determine the used cross size of each flex item
// https://drafts.csswg.org/css-flexbox/#algo-stretch
let (item_used_cross_sizes, item_results): (Vec<_>, Vec<_>) = self
.items
.iter_mut()
.zip(item_layout_results)
.zip(&item_used_main_sizes)
.map(|((item, mut item_result), &used_main_size)| {
let has_stretch = item.align_self == AlignItems::Stretch;
let cross_size = if has_stretch &&
item.content_box_size.cross.is_auto() &&
!(item.margin.cross_start.is_auto() || item.margin.cross_end.is_auto())
{
(line_cross_size - item.pbm_auto_is_zero.cross.into()).clamp_between_extremums(
item.content_min_size.cross,
item.content_max_size.cross,
)
} else {
item_result.hypothetical_cross_size
};
if has_stretch {
// “If the flex item has `align-self: stretch`, redo layout for its contents,
// treating this used size as its definite cross size
// so that percentage-sized children can be resolved.”
item_result = item.layout(used_main_size, flex_context, Some(cross_size));
}
(cross_size, item_result)
})
.unzip();
// Distribute any remaining free space
// https://drafts.csswg.org/css-flexbox/#algo-main-align
let (item_main_margins, free_space_distributed) =
self.resolve_auto_main_margins(remaining_free_space);
// Align the items along the main-axis per justify-content.
let item_count = self.items.len();
let main_start_position = if free_space_distributed {
Length::zero()
} else {
match flex_context.justify_content {
JustifyContent::FlexEnd => remaining_free_space,
JustifyContent::Center => remaining_free_space / 2.0,
JustifyContent::SpaceAround => remaining_free_space / (item_count * 2) as CSSFloat,
_ => Length::zero(),
}
};
let item_main_interval = if free_space_distributed {
Length::zero()
} else {
match flex_context.justify_content {
JustifyContent::SpaceBetween => {
if item_count > 1 {
remaining_free_space / (item_count - 1) as CSSFloat
} else {
Length::zero()
}
},
JustifyContent::SpaceAround => remaining_free_space / item_count as CSSFloat,
_ => Length::zero(),
}
};
// https://drafts.csswg.org/css-flexbox/#algo-cross-margins
let item_cross_margins = self.items.iter().zip(&item_used_cross_sizes).map(
|(item, &item_cross_content_size)| {
item.resolve_auto_cross_margins(
flex_context,
line_cross_size,
item_cross_content_size,
)
},
);
let item_margins = item_main_margins
.zip(item_cross_margins)
.map(
|((main_start, main_end), (cross_start, cross_end))| FlexRelativeSides {
main_start,
main_end,
cross_start,
cross_end,
},
)
.collect::<Vec<_>>();
// https://drafts.csswg.org/css-flexbox/#algo-main-align
let items_content_main_start_positions = self.align_along_main_axis(
&item_used_main_sizes,
&item_margins,
main_start_position,
item_main_interval,
);
// https://drafts.csswg.org/css-flexbox/#algo-cross-align
let item_content_cross_start_posititons = self
.items
.iter()
.zip(&item_margins)
.zip(&item_used_cross_sizes)
.map(|((item, margin), size)| {
item.align_along_cross_axis(margin, size, line_cross_size)
});
let item_fragments = self
.items
.iter()
.zip(item_results)
.zip(
item_used_main_sizes
.iter()
.zip(&item_used_cross_sizes)
.map(|(&main, &cross)| FlexRelativeVec2 { main, cross })
.zip(
items_content_main_start_positions
.zip(item_content_cross_start_posititons)
.map(|(main, cross)| FlexRelativeVec2 { main, cross }),
)
.map(|(size, start_corner)| FlexRelativeRect { size, start_corner }),
)
.zip(&item_margins)
.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);
(
// TODO: We should likely propagate baselines from `display: flex`.
BoxFragment::new(
item.box_.base_fragment_info(),
item.box_.style().clone(),
item_result.fragments,
content_rect,
flex_context.sides_to_flow_relative(item.padding.map(|t| (*t).into())),
flex_context.sides_to_flow_relative(item.border.map(|t| (*t).into())),
margin,
None, /* clearance */
collapsed_margin,
),
item_result.positioning_context,
)
})
.collect();
FlexLineLayoutResult {
cross_size: line_cross_size,
item_fragments,
}
}
/// Return the *main size* of each item, and the line’s remainaing free space
/// <https://drafts.csswg.org/css-flexbox/#resolve-flexible-lengths>
fn resolve_flexible_lengths(&self, container_main_size: Length) -> (Vec<Length>, Length) {
let mut frozen = vec![false; self.items.len()];
let mut target_main_sizes_vec = self
.items
.iter()
.map(|item| item.flex_base_size)
.collect::<Vec<_>>();
// Using `Cell`s reconciles mutability with multiple borrows in closures
let target_main_sizes = Cell::from_mut(&mut *target_main_sizes_vec).as_slice_of_cells();
let frozen = Cell::from_mut(&mut *frozen).as_slice_of_cells();
let frozen_count = Cell::new(0);
let grow = self.outer_hypothetical_main_sizes_sum < container_main_size;
let flex_factor = |item: &FlexItem| {
let position_style = item.box_.style().get_position();
if grow {
position_style.flex_grow.0
} else {
position_style.flex_shrink.0
}
};
let items = || self.items.iter().zip(target_main_sizes).zip(frozen);
// “Size inflexible items”
for ((item, target_main_size), frozen) in items() {
let is_inflexible = flex_factor(item) == 0. ||
if grow {
item.flex_base_size > item.hypothetical_main_size
} else {
item.flex_base_size < item.hypothetical_main_size
};
if is_inflexible {
frozen_count.set(frozen_count.get() + 1);
frozen.set(true);
target_main_size.set(item.hypothetical_main_size);
}
}
let check_for_flexible_items = || frozen_count.get() < self.items.len();
let free_space = || {
container_main_size -
items()
.map(|((item, target_main_size), frozen)| {
item.pbm_auto_is_zero.main +
if frozen.get() {
target_main_size.get().into()
} else {
item.flex_base_size.into()
}
})
.map(|t| t.into())
.sum()
};
// https://drafts.csswg.org/css-flexbox/#initial-free-space
let initial_free_space = free_space();
let unfrozen_items = || {
items().filter_map(|(item_and_target_main_size, frozen)| {
if !frozen.get() {
Some(item_and_target_main_size)
} else {
None
}
})
};
loop {
// https://drafts.csswg.org/css-flexbox/#remaining-free-space
let mut remaining_free_space = free_space();
if !check_for_flexible_items() {
return (target_main_sizes_vec, remaining_free_space);
}
let unfrozen_items_flex_factor_sum: f32 =
unfrozen_items().map(|(item, _)| flex_factor(item)).sum();
// FIXME: I (Simon) transcribed the spec but I don’t yet understand why this algorithm
if unfrozen_items_flex_factor_sum < 1. {
let multiplied = initial_free_space * unfrozen_items_flex_factor_sum;
if multiplied.abs() < remaining_free_space.abs() {
remaining_free_space = multiplied
}
}
// “Distribute free space proportional to the flex factors.”
// FIXME: is it a problem if floating point precision errors accumulate
// and we get not-quite-zero remaining free space when we should get zero here?
if remaining_free_space != Length::zero() {
if grow {
for (item, target_main_size) in unfrozen_items() {
let grow_factor = item.box_.style().get_position().flex_grow.0;
let ratio = grow_factor / unfrozen_items_flex_factor_sum;
target_main_size.set(item.flex_base_size + remaining_free_space * ratio);
}
} else {
// https://drafts.csswg.org/css-flexbox/#scaled-flex-shrink-factor
let scaled_shrink_factor = |item: &FlexItem| {
let shrink_factor = item.box_.style().get_position().flex_shrink.0;
item.flex_base_size * shrink_factor
};
let scaled_shrink_factors_sum: Length = unfrozen_items()
.map(|(item, _)| scaled_shrink_factor(item))
.sum();
if scaled_shrink_factors_sum > Length::zero() {
for (item, target_main_size) in unfrozen_items() {
let ratio = scaled_shrink_factor(item) / scaled_shrink_factors_sum;
target_main_size
.set(item.flex_base_size - remaining_free_space.abs() * ratio);
}
}
}
}
// “Fix min/max violations.”
let violation = |(item, target_main_size): (&FlexItem, &Cell<Length>)| {
let size = target_main_size.get();
let clamped = size.clamp_between_extremums(
item.content_min_size.main,
item.content_max_size.main,
);
clamped - size
};
// “Freeze over-flexed items.”
let total_violation: Length = unfrozen_items().map(violation).sum();
if total_violation == Length::zero() {
// “Freeze all items.”