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LibWeb: Make sure that margins don't collapse across a nested BFC

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In order to fix this, I also had to reorganize the code so that we
create an independent formatting context even for block-level boxes
that don't have any children. This accidentally improves a table
layout test as well (for empty tables).
This commit is contained in:
Andreas Kling 2023-05-19 13:48:47 +02:00
parent 9ce7681ff2
commit 411b28fc59
Notes: sideshowbarker 2024-07-17 07:06:47 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/411b28fc59
Pull-request: https://github.com/SerenityOS/serenity/pull/18918
4 changed files with 62 additions and 31 deletions
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6
Tests/LibWeb/Layout/expected/block-and-inline/margin-must-not-collapse-across-nested-bfc.txt Normal file
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@ -0,0 +1,6 @@
Viewport <#document> at (0,0) content-size 800x600 children: not-inline
BlockContainer <html> at (0,0) content-size 800x116 [BFC] children: not-inline
BlockContainer <body> at (8,30) content-size 784x100 children: not-inline
BlockContainer <div.not-bfc> at (8,30) content-size 784x20 children: not-inline
BlockContainer <div.bfc> at (8,80) content-size 784x0 [BFC] children: not-inline
BlockContainer <div.not-bfc> at (8,110) content-size 784x20 children: not-inline

4
Tests/LibWeb/Layout/expected/table/basic.txt
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@ -1,8 +1,8 @@
Viewport <#document> at (0,0) content-size 800x600 children: not-inline
BlockContainer <html> at (0,0) content-size 800x600 [BFC] children: not-inline
BlockContainer <body> at (8,8) content-size 784x58.40625 children: not-inline
TableWrapper <(anonymous)> at (8,8) content-size 784x0 [BFC] children: not-inline
TableBox <table#empty-table> at (8,8) content-size 784x0 [TFC] children: not-inline
TableWrapper <(anonymous)> at (8,8) content-size 0x0 [BFC] children: not-inline
TableBox <table#empty-table> at (8,8) content-size 0x0 [TFC] children: not-inline
BlockContainer <(anonymous)> at (8,8) content-size 784x0 children: inline
TextNode <#text>
TextNode <#text>

20
Tests/LibWeb/Layout/input/block-and-inline/margin-must-not-collapse-across-nested-bfc.html Normal file
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@ -0,0 +1,20 @@
<!doctype html><style>
* {
padding: 0;
}
html {
background: white;
}
body {
background: pink;
}
.not-bfc {
margin-top: 30px;
height: 20px;
background: orange;
}
.bfc {
margin-top: 30px;
display: flow-root;
}
</style><div class="not-bfc"></div><div class=bfc></div><div class="not-bfc"></div>

63
Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
View File

@ -552,13 +552,23 @@ void BlockFormattingContext::layout_block_level_box(Box const& box, BlockContain
m_margin_state.reset();
}
m_margin_state.add_margin(box_state.margin_top);
m_margin_state.update_block_waiting_for_final_y_position();
CSSPixels margin_top = 0;
auto independent_formatting_context = create_independent_formatting_context_if_needed(m_state, box);
auto margin_top = m_margin_state.current_collapsed_margin();
if (m_margin_state.has_block_container_waiting_for_final_y_position()) {
// If first child margin top will collapse with margin-top of containing block then margin-top of child is 0
margin_top = 0;
if (independent_formatting_context) {
// Margins of elements that establish new formatting contexts do not collapse with their in-flow children
m_margin_state.reset();
margin_top = box_state.margin_top;
} else {
m_margin_state.add_margin(box_state.margin_top);
m_margin_state.update_block_waiting_for_final_y_position();
margin_top = m_margin_state.current_collapsed_margin();
if (m_margin_state.has_block_container_waiting_for_final_y_position()) {
// If first child margin top will collapse with margin-top of containing block then margin-top of child is 0
margin_top = 0;
}
}
place_block_level_element_in_normal_flow_vertically(box, y + margin_top);
@ -567,36 +577,31 @@ void BlockFormattingContext::layout_block_level_box(Box const& box, BlockContain
place_block_level_element_in_normal_flow_horizontally(box, available_space);
OwnPtr<FormattingContext> independent_formatting_context;
if (!box.is_replaced_box() && box.has_children()) {
independent_formatting_context = create_independent_formatting_context_if_needed(m_state, box);
if (independent_formatting_context) {
// Margins of elements that establish new formatting contexts do not collapse with their in-flow children
m_margin_state.reset();
independent_formatting_context->run(box, layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
if (independent_formatting_context) {
// This box establishes a new formatting context. Pass control to it.
independent_formatting_context->run(box, layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
} else {
// This box participates in the current block container's flow.
if (box.children_are_inline()) {
layout_inline_children(verify_cast<BlockContainer>(box), layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
} else {
if (box.children_are_inline()) {
layout_inline_children(verify_cast<BlockContainer>(box), layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
} else {
if (box_state.border_top > 0 || box_state.padding_top > 0) {
// margin-top of block container can't collapse with it's children if it has non zero border or padding
m_margin_state.reset();
} else if (!m_margin_state.has_block_container_waiting_for_final_y_position()) {
// margin-top of block container can be updated during children layout hence it's final y position yet to be determined
m_margin_state.register_block_container_y_position_update_callback([&](CSSPixels margin_top) {
place_block_level_element_in_normal_flow_vertically(box, margin_top + y + box_state.border_box_top());
});
}
layout_block_level_children(verify_cast<BlockContainer>(box), layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
if (box_state.border_top > 0 || box_state.padding_top > 0) {
// margin-top of block container can't collapse with it's children if it has non zero border or padding
m_margin_state.reset();
} else if (!m_margin_state.has_block_container_waiting_for_final_y_position()) {
// margin-top of block container can be updated during children layout hence it's final y position yet to be determined
m_margin_state.register_block_container_y_position_update_callback([&](CSSPixels margin_top) {
place_block_level_element_in_normal_flow_vertically(box, margin_top + y + box_state.border_box_top());
});
}
layout_block_level_children(verify_cast<BlockContainer>(box), layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
}
}
compute_height(box, available_space);
if (!margins_collapse_through(box, m_state)) {
if (independent_formatting_context || !margins_collapse_through(box, m_state)) {
if (!m_margin_state.box_last_in_flow_child_margin_bottom_collapsed) {
m_margin_state.reset();
}