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LibWeb: Make FC of containing block responsible for abspos layout

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Before this change, a formatting context was responsible for layout of
absolutely positioned boxes whose FC root box was their parent (either
directly or indirectly). This only worked correctly when the containing
block of the absolutely positioned child did not escape the FC root.
This is because the width and height of an absolutely positioned box are
resolved based on the size of its containing block, so we needed to
ensure that the containing block's layout was completed before laying
out an absolutely positioned box.

With this change, the layout of absolutely positioned boxes is delayed
until the FC responsible for the containing block's layout is complete.
This has affected the way we calculate the static position. It is no
longer possible to ask the FC for a box's static position, as this FC's
state might be gone by the time the layout for absolutely positioned
elements occurs. Instead, the "static position rectangle" (a concept
from the spec) is saved in the layout state, along with information on
how to align the box within this rectangle when its width and height are
resolved.
This commit is contained in:
Aliaksandr Kalenik 2024-09-10 19:02:03 +02:00 • committed by Andreas Kling
commit 863416e3ac
Notes: github-actions[bot] 2024-09-12 05:37:23 +00:00
18 changed files with 299 additions and 86 deletions
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20
Userland/Libraries/LibWeb/Layout/FormattingContext.cpp
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@ -716,7 +716,7 @@ void FormattingContext::compute_width_for_absolutely_positioned_non_replaced_ele
width = CSS::Length::make_px(content_width);
m_state.get_mutable(box).set_content_width(content_width);
auto static_position = calculate_static_position(box);
auto static_position = m_state.get(box).static_position();
left = static_position.x();
right = solve_for_right();
@ -774,7 +774,7 @@ void FormattingContext::compute_width_for_absolutely_positioned_non_replaced_ele
// Then solve for 'left' (if 'direction is 'rtl') or 'right' (if 'direction' is 'ltr').
else if (computed_left.is_auto() && computed_right.is_auto() && !width.is_auto()) {
// FIXME: Check direction
auto static_position = calculate_static_position(box);
auto static_position = m_state.get(box).static_position();
left = static_position.x();
right = solve_for_right();
}
@ -863,7 +863,7 @@ void FormattingContext::compute_width_for_absolutely_positioned_replaced_element
auto margin_left = computed_values.margin().left();
auto right = computed_values.inset().right();
auto margin_right = computed_values.margin().right();
auto static_position = calculate_static_position(box);
auto static_position = m_state.get(box).static_position();
auto to_px = [&](const CSS::LengthPercentage& l) {
return l.to_px(box, width_of_containing_block);
@ -1034,7 +1034,7 @@ void FormattingContext::compute_height_for_absolutely_positioned_non_replaced_el
auto constrained_height = apply_min_max_height_constraints(height);
m_state.get_mutable(box).set_content_height(constrained_height.to_px(box));
auto static_position = calculate_static_position(box);
auto static_position = m_state.get(box).static_position();
top = CSS::Length::make_px(static_position.y());
solve_for_bottom();
@ -1089,7 +1089,7 @@ void FormattingContext::compute_height_for_absolutely_positioned_non_replaced_el
// 2. If top and bottom are auto and height is not auto,
else if (top.is_auto() && bottom.is_auto() && !height.is_auto()) {
// then set top to the static position,
top = CSS::Length::make_px(calculate_static_position(box).y());
top = CSS::Length::make_px(m_state.get(box).static_position().y());
// then solve for bottom.
solve_for_bottom();
@ -1176,7 +1176,7 @@ CSSPixelRect FormattingContext::content_box_rect_in_static_position_ancestor_coo
}
// https://www.w3.org/TR/css-position-3/#staticpos-rect
CSSPixelPoint FormattingContext::calculate_static_position(Box const& box) const
StaticPositionRect FormattingContext::calculate_static_position_rect(Box const& box) const
{
// NOTE: This is very ad-hoc.
// The purpose of this function is to calculate the approximate position that `box`
@ -1216,7 +1216,9 @@ CSSPixelPoint FormattingContext::calculate_static_position(Box const& box) const
y = box_state.vertical_offset_of_parent_block_container;
}
auto offset_to_static_parent = content_box_rect_in_static_position_ancestor_coordinate_space(box, *box.containing_block());
return offset_to_static_parent.location().translated(x, y);
StaticPositionRect static_position_rect;
static_position_rect.rect = { offset_to_static_parent.location().translated(x, y), { 0, 0 } };
return static_position_rect;
}
void FormattingContext::layout_absolutely_positioned_element(Box const& box, AvailableSpace const& available_space)
@ -1259,7 +1261,7 @@ void FormattingContext::layout_absolutely_positioned_element(Box const& box, Ava
CSSPixelPoint used_offset;
auto static_position = calculate_static_position(box);
auto static_position = m_state.get(box).static_position();
if (box.computed_values().inset().top().is_auto() && box.computed_values().inset().bottom().is_auto()) {
used_offset.set_y(static_position.y());
@ -1300,7 +1302,7 @@ void FormattingContext::compute_height_for_absolutely_positioned_replaced_elemen
auto margin_top = computed_values.margin().top();
auto bottom = computed_values.inset().bottom();
auto margin_bottom = computed_values.margin().bottom();
auto static_position = calculate_static_position(box);
auto static_position = m_state.get(box).static_position();
auto to_px = [&](const CSS::LengthPercentage& l) {
return l.to_px(box, height_of_containing_block);