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LibWeb: Move absolute positioning up to FormattingContext

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It seems like both BFC and IFC can have absolutely positioned children.
It's a bit strange, but consider the following HTML:

<html><body>foobar<img style="position: absolute"></body></html>

In such a document, the <img> element is an absolutely positioned child
of a block-level element (<body>) with no block-level children.
An IFC is established for <body>, and needs to handle layout for <img>.
This commit is contained in:
Andreas Kling 2021-01-06 18:18:46 +01:00
parent 4c98d00bef
commit 0ecefbff57
5 changed files with 281 additions and 215 deletions
Download patch file Download diff file Expand all files Collapse all files

218
Libraries/LibWeb/Layout/BlockFormattingContext.cpp
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@ -76,7 +76,7 @@ void BlockFormattingContext::run(Box& box, LayoutMode layout_mode)
box.for_each_child_of_type<Box>([&](auto& child_box) {
if (child_box.is_absolutely_positioned()) {
layout_absolutely_positioned_child(child_box);
layout_absolutely_positioned_element(child_box);
}
return IterationDecision::Continue;
});
@ -85,6 +85,11 @@ void BlockFormattingContext::run(Box& box, LayoutMode layout_mode)
void BlockFormattingContext::compute_width(Box& box)
{
if (box.is_absolutely_positioned()) {
compute_width_for_absolutely_positioned_element(box);
return;
}
if (is<ReplacedBox>(box)) {
// FIXME: This should not be done *by* ReplacedBox
auto& replaced = downcast<ReplacedBox>(box);
@ -93,11 +98,6 @@ void BlockFormattingContext::compute_width(Box& box)
return;
}
if (box.is_absolutely_positioned()) {
compute_width_for_absolutely_positioned_block(box);
return;
}
if (box.is_floating()) {
compute_width_for_floating_box(box);
return;
@ -272,146 +272,6 @@ void BlockFormattingContext::compute_height_for_block_level_replaced_element_in_
box.set_height(compute_height_for_replaced_element(box));
}
void BlockFormattingContext::compute_width_for_absolutely_positioned_block(Box& box)
{
auto& containing_block = *box.containing_block();
auto& computed_values = box.computed_values();
auto zero_value = CSS::Length::make_px(0);
auto margin_left = CSS::Length::make_auto();
auto margin_right = CSS::Length::make_auto();
const auto border_left = computed_values.border_left().width;
const auto border_right = computed_values.border_right().width;
const auto padding_left = computed_values.padding().left.resolved_or_zero(box, containing_block.width());
const auto padding_right = computed_values.padding().right.resolved_or_zero(box, containing_block.width());
auto try_compute_width = [&](const auto& a_width) {
margin_left = computed_values.margin().left.resolved_or_zero(box, containing_block.width());
margin_right = computed_values.margin().right.resolved_or_zero(box, containing_block.width());
auto left = computed_values.offset().left.resolved_or_auto(box, containing_block.width());
auto right = computed_values.offset().right.resolved_or_auto(box, containing_block.width());
auto width = a_width;
auto solve_for_left = [&] {
return CSS::Length(containing_block.width() - margin_left.to_px(box) - border_left - padding_left.to_px(box) - width.to_px(box) - padding_right.to_px(box) - border_right - margin_right.to_px(box) - right.to_px(box), CSS::Length::Type::Px);
};
auto solve_for_width = [&] {
return CSS::Length(containing_block.width() - left.to_px(box) - margin_left.to_px(box) - border_left - padding_left.to_px(box) - padding_right.to_px(box) - border_right - margin_right.to_px(box) - right.to_px(box), CSS::Length::Type::Px);
};
auto solve_for_right = [&] {
return CSS::Length(containing_block.width() - left.to_px(box) - margin_left.to_px(box) - border_left - padding_left.to_px(box) - width.to_px(box) - padding_right.to_px(box) - border_right - margin_right.to_px(box), CSS::Length::Type::Px);
};
// If all three of 'left', 'width', and 'right' are 'auto':
if (left.is_auto() && width.is_auto() && right.is_auto()) {
// First set any 'auto' values for 'margin-left' and 'margin-right' to 0.
if (margin_left.is_auto())
margin_left = CSS::Length::make_px(0);
if (margin_right.is_auto())
margin_right = CSS::Length::make_px(0);
// Then, if the 'direction' property of the element establishing the static-position containing block
// is 'ltr' set 'left' to the static position and apply rule number three below;
// otherwise, set 'right' to the static position and apply rule number one below.
// FIXME: This is very hackish.
left = CSS::Length::make_px(0);
goto Rule3;
}
if (!left.is_auto() && !width.is_auto() && !right.is_auto()) {
// FIXME: This should be solved in a more complicated way.
return width;
}
if (margin_left.is_auto())
margin_left = CSS::Length::make_px(0);
if (margin_right.is_auto())
margin_right = CSS::Length::make_px(0);
// 1. 'left' and 'width' are 'auto' and 'right' is not 'auto',
// then the width is shrink-to-fit. Then solve for 'left'
if (left.is_auto() && width.is_auto() && !right.is_auto()) {
auto result = calculate_shrink_to_fit_widths(box);
solve_for_left();
auto available_width = solve_for_width();
width = CSS::Length(min(max(result.preferred_minimum_width, available_width.to_px(box)), result.preferred_width), CSS::Length::Type::Px);
}
// 2. 'left' and 'right' are 'auto' and 'width' is not 'auto',
// then if the 'direction' property of the element establishing
// the static-position containing block is 'ltr' set 'left'
// to the static position, otherwise set 'right' to the static position.
// Then solve for 'left' (if 'direction is 'rtl') or 'right' (if 'direction' is 'ltr').
else if (left.is_auto() && right.is_auto() && !width.is_auto()) {
// FIXME: Check direction
// FIXME: Use the static-position containing block
left = zero_value;
right = solve_for_right();
}
// 3. 'width' and 'right' are 'auto' and 'left' is not 'auto',
// then the width is shrink-to-fit. Then solve for 'right'
else if (width.is_auto() && right.is_auto() && !left.is_auto()) {
Rule3:
auto result = calculate_shrink_to_fit_widths(box);
auto available_width = solve_for_width();
width = CSS::Length(min(max(result.preferred_minimum_width, available_width.to_px(box)), result.preferred_width), CSS::Length::Type::Px);
right = solve_for_right();
}
// 4. 'left' is 'auto', 'width' and 'right' are not 'auto', then solve for 'left'
else if (left.is_auto() && !width.is_auto() && !right.is_auto()) {
left = solve_for_left();
}
// 5. 'width' is 'auto', 'left' and 'right' are not 'auto', then solve for 'width'
else if (width.is_auto() && !left.is_auto() && !right.is_auto()) {
width = solve_for_width();
}
// 6. 'right' is 'auto', 'left' and 'width' are not 'auto', then solve for 'right'
else if (right.is_auto() && !left.is_auto() && !width.is_auto()) {
right = solve_for_right();
}
return width;
};
auto specified_width = computed_values.width().resolved_or_auto(box, containing_block.width());
// 1. The tentative used width is calculated (without 'min-width' and 'max-width')
auto used_width = try_compute_width(specified_width);
// 2. The tentative used width is greater than 'max-width', the rules above are applied again,
// but this time using the computed value of 'max-width' as the computed value for 'width'.
auto specified_max_width = computed_values.max_width().resolved_or_auto(box, containing_block.width());
if (!specified_max_width.is_auto()) {
if (used_width.to_px(box) > specified_max_width.to_px(box)) {
used_width = try_compute_width(specified_max_width);
}
}
// 3. If the resulting width is smaller than 'min-width', the rules above are applied again,
// but this time using the value of 'min-width' as the computed value for 'width'.
auto specified_min_width = computed_values.min_width().resolved_or_auto(box, containing_block.width());
if (!specified_min_width.is_auto()) {
if (used_width.to_px(box) < specified_min_width.to_px(box)) {
used_width = try_compute_width(specified_min_width);
}
}
box.set_width(used_width.to_px(box));
box.box_model().margin.left = margin_left.to_px(box);
box.box_model().margin.right = margin_right.to_px(box);
box.box_model().border.left = border_left;
box.box_model().border.right = border_right;
box.box_model().padding.left = padding_left.to_px(box);
box.box_model().padding.right = padding_right.to_px(box);
}
void BlockFormattingContext::compute_height(Box& box)
{
if (is<ReplacedBox>(box)) {
@ -703,70 +563,4 @@ void BlockFormattingContext::layout_floating_child(Box& box, Box& containing_blo
box.set_offset(x, box.effective_offset().y());
}
void BlockFormattingContext::layout_absolutely_positioned_child(Box& box)
{
auto& containing_block = context_box();
auto& box_model = box.box_model();
auto specified_width = box.computed_values().width().resolved_or_auto(box, containing_block.width());
compute_width(box);
layout_inside(box, LayoutMode::Default);
compute_height(box);
box_model.margin.left = box.computed_values().margin().left.resolved_or_auto(box, containing_block.width()).to_px(box);
box_model.margin.top = box.computed_values().margin().top.resolved_or_auto(box, containing_block.height()).to_px(box);
box_model.margin.right = box.computed_values().margin().right.resolved_or_auto(box, containing_block.width()).to_px(box);
box_model.margin.bottom = box.computed_values().margin().bottom.resolved_or_auto(box, containing_block.height()).to_px(box);
box_model.border.left = box.computed_values().border_left().width;
box_model.border.right = box.computed_values().border_right().width;
box_model.border.top = box.computed_values().border_top().width;
box_model.border.bottom = box.computed_values().border_bottom().width;
box_model.offset.left = box.computed_values().offset().left.resolved_or_auto(box, containing_block.width()).to_px(box);
box_model.offset.top = box.computed_values().offset().top.resolved_or_auto(box, containing_block.height()).to_px(box);
box_model.offset.right = box.computed_values().offset().right.resolved_or_auto(box, containing_block.width()).to_px(box);
box_model.offset.bottom = box.computed_values().offset().bottom.resolved_or_auto(box, containing_block.height()).to_px(box);
if (box.computed_values().offset().left.is_auto() && specified_width.is_auto() && box.computed_values().offset().right.is_auto()) {
if (box.computed_values().margin().left.is_auto())
box_model.margin.left = 0;
if (box.computed_values().margin().right.is_auto())
box_model.margin.right = 0;
}
Gfx::FloatPoint used_offset;
if (!box.computed_values().offset().left.is_auto()) {
float x_offset = box_model.offset.left
+ box_model.border_box().left;
used_offset.set_x(x_offset + box_model.margin.left);
} else if (!box.computed_values().offset().right.is_auto()) {
float x_offset = 0
- box_model.offset.right
- box_model.border_box().right;
used_offset.set_x(containing_block.width() + x_offset - box.width() - box_model.margin.right);
} else {
float x_offset = box_model.margin_box().left;
used_offset.set_x(x_offset);
}
if (!box.computed_values().offset().top.is_auto()) {
float y_offset = box_model.offset.top
+ box_model.border_box().top;
used_offset.set_y(y_offset + box_model.margin.top);
} else if (!box.computed_values().offset().bottom.is_auto()) {
float y_offset = 0
- box_model.offset.bottom
- box_model.border_box().bottom;
used_offset.set_y(containing_block.height() + y_offset - box.height() - box_model.margin.bottom);
} else {
float y_offset = box_model.margin_box().top;
used_offset.set_y(y_offset);
}
box.set_offset(used_offset);
}
}