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LibWeb: Use fit-content width in place of indefinite flex item widths

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In `flex-direction: column` layouts, a flex item's intrinsic height may
depend on its width, but the width is calculated *after* the intrinsic
height is required.

Unfortunately, the specification doesn't tell us exactly what to do here
(missing inputs to intrinsic sizing is a common problem) so we take the
solution that flexbox applies in 9.2.3.C and apply it to all intrinsic
height calculations within FlexFormattingContext: if the used width of
an item is not yet known when its intrinsic height is requested, we
substitute the fit-content width instead.

Note that while this is technically ad-hoc, it's basically extrapolating
the spec's suggestion in one specific case and using it in all cases.
This commit is contained in:
Andreas Kling 2023-03-27 20:56:20 +02:00
parent ca290b27ea
commit af118abdf0
4 changed files with 79 additions and 56 deletions
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22
Tests/LibWeb/Layout/expected/flex-column-item-with-auto-height-depending-on-auto-width.txt Normal file
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@ -0,0 +1,22 @@
Viewport <#document> at (0,0) content-size 800x600 children: not-inline
BlockContainer <html> at (1,1) content-size 798x457.09375 children: not-inline
Box <body.hero> at (10,10) content-size 500x439.09375 flex-container(column) children: not-inline
BlockContainer <div.upper> at (10,11) content-size 500x437.09375 flex-item children: inline
line 0 width: 453.984375, height: 87.34375, bottom: 87.34375, baseline: 67.65625
frag 0 from TextNode start: 0, length: 11, rect: [10,11 453.984375x87.34375]
"This entire"
line 1 width: 455, height: 87.6875, bottom: 175.03125, baseline: 67.65625
frag 0 from TextNode start: 12, length: 11, rect: [10,98 455x87.34375]
"text should"
line 2 width: 230.78125, height: 88.03125, bottom: 262.71875, baseline: 67.65625
frag 0 from TextNode start: 24, length: 5, rect: [10,185 230.78125x87.34375]
"be on"
line 3 width: 272.109375, height: 87.375, bottom: 349.40625, baseline: 67.65625
frag 0 from TextNode start: 30, length: 6, rect: [10,273 272.109375x87.34375]
"orange"
line 4 width: 468.75, height: 87.71875, bottom: 437.09375, baseline: 67.65625
frag 0 from TextNode start: 37, length: 11, rect: [10,360 468.75x87.34375]
"background."
TextNode <#text>
BlockContainer <(anonymous)> at (10,10) content-size 0x0 children: inline
TextNode <#text>

15
Tests/LibWeb/Layout/input/flex-column-item-with-auto-height-depending-on-auto-width.html Normal file
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@ -0,0 +1,15 @@
<!DOCTYPE html><html><head><style>
* {
border: 1px solid black;
font: 80px SerenitySans;
}
.hero {
display: flex;
flex-direction: column;
align-items: center;
width: 500px;
}
.upper {
background: orange;
}
</style></head><body class="hero"><div class="upper">This entire text should be on orange background.</div></div>

97
Userland/Libraries/LibWeb/Layout/FlexFormattingContext.cpp
View file

@ -545,48 +545,6 @@ void FlexFormattingContext::determine_available_space_for_items(AvailableSpace c
}
}
CSSPixels FlexFormattingContext::calculate_indefinite_main_size(FlexItem const& item)
{
VERIFY(!has_definite_main_size(item.box));
// Otherwise, size the item into the available space using its used flex basis in place of its main size,
// treating a value of content as max-content.
if (item.used_flex_basis.type == CSS::FlexBasis::Content)
return calculate_max_content_main_size(item);
// If a cross size is needed to determine the main size
// (e.g. when the flex item’s main size is in its block axis, or when it has a preferred aspect ratio)
// and the flex item’s cross size is auto and not definite,
// in this calculation use fit-content as the flex item’s cross size.
// The flex base size is the item’s resulting main size.
bool main_size_is_in_block_axis = !is_row_layout();
// FIXME: Figure out if we have a preferred aspect ratio.
bool has_preferred_aspect_ratio = false;
bool cross_size_needed_to_determine_main_size = main_size_is_in_block_axis || has_preferred_aspect_ratio;
if (cross_size_needed_to_determine_main_size) {
// Figure out the fit-content cross size, then layout with that and see what height comes out of it.
CSSPixels fit_content_cross_size = calculate_fit_content_cross_size(item);
LayoutState throwaway_state(&m_state);
auto& box_state = throwaway_state.get_mutable(item.box);
// Item has definite cross size, layout with that as the used cross size.
auto independent_formatting_context = create_independent_formatting_context_if_needed(throwaway_state, item.box);
// NOTE: Flex items should always create an independent formatting context!
VERIFY(independent_formatting_context);
box_state.set_content_width(fit_content_cross_size);
independent_formatting_context->run(item.box, LayoutMode::Normal, m_available_space_for_items->space);
return independent_formatting_context->automatic_content_height();
}
return calculate_fit_content_main_size(item);
}
// https://drafts.csswg.org/css-flexbox-1/#propdef-flex-basis
CSS::FlexBasisData FlexFormattingContext::used_flex_basis_for_item(FlexItem const& item) const
{
@ -685,12 +643,31 @@ void FlexFormattingContext::determine_flex_base_size_and_hypothetical_main_size(
// (e.g. when the flex item’s main size is in its block axis) and the flex item’s cross size is auto and not definite,
// in this calculation use fit-content as the flex item’s cross size.
// The flex base size is the item’s resulting main size.
// FIXME: This is probably too naive.
// FIXME: Care about FlexBasis::Auto
if (has_definite_main_size(child_box))
return resolved_definite_main_size(item);
return calculate_indefinite_main_size(item);
// NOTE: If the flex item has a definite main size, just use that as the flex base size.
if (has_definite_main_size(child_box))
return inner_main_size(child_box);
// NOTE: There's a fundamental problem with many CSS specifications in that they neglect to mention
// which width to provide when calculating the intrinsic height of a box in various situations.
// Spec bug: https://github.com/w3c/csswg-drafts/issues/2890
// NOTE: This is one of many situations where that causes trouble: if this is a flex column layout,
// we may need to calculate the intrinsic height of a flex item. This requires a width, but a
// width won't be determined until later on in the flex layout algorithm.
// In the specific case above (E), the spec mentions using `fit-content` if "a cross size is
// needed to determine the main size", so that's exactly what we do.
// NOTE: Substituting the fit-content size actually happens elsewhere, in the various helpers that
// calculate the intrinsic sizes of a flex item, e.g. calculate_min_content_main_size().
// This means that *all* intrinsic heights computed within a flex formatting context will
// automatically use the fit-content width in case a used width is not known yet.
if (item.used_flex_basis.type == CSS::FlexBasis::Content) {
return calculate_max_content_main_size(item);
}
return calculate_fit_content_main_size(item);
}();
// The hypothetical main size is the item’s flex base size clamped according to its used min and max main sizes (and flooring the content box size at zero).
@ -1868,7 +1845,10 @@ CSSPixels FlexFormattingContext::calculate_min_content_main_size(FlexItem const&
if (is_row_layout()) {
return calculate_min_content_width(item.box);
}
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_flex_container->space);
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_items->space);
if (available_space.width.is_indefinite()) {
available_space.width = AvailableSize::make_definite(calculate_fit_content_width(item.box, m_available_space_for_items->space));
}
return calculate_min_content_height(item.box, available_space.width);
}
@ -1877,30 +1857,34 @@ CSSPixels FlexFormattingContext::calculate_max_content_main_size(FlexItem const&
if (is_row_layout()) {
return calculate_max_content_width(item.box);
}
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_flex_container->space);
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_items->space);
if (available_space.width.is_indefinite()) {
available_space.width = AvailableSize::make_definite(calculate_fit_content_width(item.box, m_available_space_for_items->space));
}
return calculate_max_content_height(item.box, available_space.width);
}
CSSPixels FlexFormattingContext::calculate_fit_content_main_size(FlexItem const& item) const
{
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_flex_container->space);
if (is_row_layout())
return calculate_fit_content_width(item.box, available_space);
return calculate_fit_content_height(item.box, available_space);
return calculate_fit_content_width(item.box, m_available_space_for_items->space);
return calculate_fit_content_height(item.box, m_available_space_for_items->space);
}
CSSPixels FlexFormattingContext::calculate_fit_content_cross_size(FlexItem const& item) const
{
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_flex_container->space);
if (!is_row_layout())
return calculate_fit_content_width(item.box, available_space);
return calculate_fit_content_height(item.box, available_space);
return calculate_fit_content_width(item.box, m_available_space_for_items->space);
return calculate_fit_content_height(item.box, m_available_space_for_items->space);
}
CSSPixels FlexFormattingContext::calculate_min_content_cross_size(FlexItem const& item) const
{
if (is_row_layout()) {
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_flex_container->space);
if (available_space.width.is_indefinite()) {
available_space.width = AvailableSize::make_definite(calculate_fit_content_width(item.box, m_available_space_for_items->space));
}
return calculate_min_content_height(item.box, available_space.width);
}
return calculate_min_content_width(item.box);
@ -1910,6 +1894,9 @@ CSSPixels FlexFormattingContext::calculate_max_content_cross_size(FlexItem const
{
if (is_row_layout()) {
auto available_space = m_state.get(item.box).available_inner_space_or_constraints_from(m_available_space_for_flex_container->space);
if (available_space.width.is_indefinite()) {
available_space.width = AvailableSize::make_definite(calculate_fit_content_width(item.box, m_available_space_for_items->space));
}
return calculate_max_content_height(item.box, available_space.width);
}
return calculate_max_content_width(item.box);

1
Userland/Libraries/LibWeb/Layout/FlexFormattingContext.h
View file

@ -156,7 +156,6 @@ private:
void determine_available_space_for_items(AvailableSpace const&);
CSSPixels calculate_indefinite_main_size(FlexItem const&);
void determine_flex_base_size_and_hypothetical_main_size(FlexItem&);
void determine_main_size_of_flex_container();