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LibWeb: Handle case where abspos flex child position depends on height

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There's a particularly awkward case where the static position of an
abspos child of a flex container is dependent on its height. This can
happen when `align-items: center` is in effect, as we have to adjust
the abspos child's Y position by half of its height.

This patch solves the issue by reordering operations in the abspos
height resolution algorithm, to make sure that height is resolved
before the static position is calculated.
This commit is contained in:
Andreas Kling 2023-09-03 14:10:46 +02:00
parent f77256fcba
commit 50d72f0d8c
3 changed files with 57 additions and 13 deletions
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12
Tests/LibWeb/Layout/expected/flex/abspos-flex-child-with-auto-height.txt Normal file
View file

@ -0,0 +1,12 @@
Viewport <#document> at (0,0) content-size 800x600 children: not-inline
BlockContainer <html> at (0,0) content-size 800x16 [BFC] children: not-inline
Box <body> at (8,8) content-size 784x0 positioned flex-container(row) [FFC] children: not-inline
BlockContainer <div.abspos> at (8,-42) content-size 100x100 positioned [BFC] children: not-inline
BlockContainer <div.green> at (8,-42) content-size 100x200 children: inline
TextNode <#text>
ViewportPaintable (Viewport<#document>) [0,0 800x600] overflow: [0,-42 800x642]
PaintableWithLines (BlockContainer<HTML>) [0,0 800x16] overflow: [0,-42 800x200]
PaintableBox (Box<BODY>) [8,8 784x0] overflow: [8,-42 100x200]
PaintableWithLines (BlockContainer<DIV>.abspos) [8,-42 100x100] overflow: [8,-42 100x200]
PaintableWithLines (BlockContainer<DIV>.green) [8,-42 100x200]

18
Tests/LibWeb/Layout/input/flex/abspos-flex-child-with-auto-height.html Normal file
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@ -0,0 +1,18 @@
<!DOCTYPE html><style>
* { outline: black solid 1px; }
body {
position: relative;
display: flex;
align-items: center;
}
.abspos {
position: absolute;
max-height: 100px;
}
.green {
display: block;
width: 100px;
height: 200px;
background: green;
}
</style><body><div class="abspos"><div class="green">

40
Userland/Libraries/LibWeb/Layout/FormattingContext.cpp
View file

@ -823,6 +823,21 @@ void FormattingContext::compute_height_for_absolutely_positioned_non_replaced_el
// In the before pass, if it turns out we need the automatic height of the box, we abort these steps.
// This allows the box to retain an indefinite height from the perspective of inside layout.
auto apply_min_max_height_constraints = [this, &box, &available_space](CSSPixels unconstrained_height) -> CSSPixels {
auto const& computed_min_height = box.computed_values().min_height();
auto const& computed_max_height = box.computed_values().max_height();
auto constrained_height = unconstrained_height;
if (!computed_max_height.is_none()) {
auto inner_max_height = calculate_inner_height(box, available_space.height, computed_max_height);
constrained_height = min(constrained_height, inner_max_height.to_px(box));
}
if (!computed_min_height.is_auto()) {
auto inner_min_height = calculate_inner_height(box, available_space.height, computed_min_height);
constrained_height = max(constrained_height, inner_min_height.to_px(box));
}
return constrained_height;
};
auto margin_top = box.computed_values().margin().top();
auto margin_bottom = box.computed_values().margin().bottom();
auto top = box.computed_values().inset().top();
@ -888,14 +903,22 @@ void FormattingContext::compute_height_for_absolutely_positioned_non_replaced_el
margin_bottom = CSS::Length::make_px(0);
// then set top to the static position,
auto static_position = calculate_static_position(box);
top = CSS::Length::make_px(static_position.y());
// and finally apply rule number three below.
// NOTE: We actually perform these two steps in the opposite order,
// because the static position may depend on the height of the box (due to alignment properties).
auto maybe_height = compute_auto_height_for_absolutely_positioned_element(box, available_space, before_or_after_inside_layout);
if (!maybe_height.has_value())
return;
height = CSS::Size::make_px(maybe_height.value());
auto constrained_height = apply_min_max_height_constraints(maybe_height.value());
m_state.get_mutable(box).set_content_height(constrained_height);
auto static_position = calculate_static_position(box);
top = CSS::Length::make_px(static_position.y());
solve_for_bottom();
}
@ -993,17 +1016,8 @@ void FormattingContext::compute_height_for_absolutely_positioned_non_replaced_el
} else {
used_height = calculate_inner_height(box, available_space.height, height).to_px(box);
}
auto const& computed_min_height = box.computed_values().min_height();
auto const& computed_max_height = box.computed_values().max_height();
if (!computed_max_height.is_none()) {
auto inner_max_height = calculate_inner_height(box, available_space.height, computed_max_height);
used_height = min(used_height, inner_max_height.to_px(box));
}
if (!computed_min_height.is_auto()) {
auto inner_min_height = calculate_inner_height(box, available_space.height, computed_min_height);
used_height = max(used_height, inner_min_height.to_px(box));
}
used_height = apply_min_max_height_constraints(used_height);
// NOTE: The following is not directly part of any spec, but this is where we resolve
// the final used values for vertical margin/border/padding.