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LibWeb: Collapse top and bottom margin of empty sibling blocks

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Margin collapsing is a bit confusing, but if I understand correctly,
when collapsing a box's top margin with the vertically adjacent
sibling box above, we should "skip over" empty (0-height) boxes and
collapse their margin with *their* vertically adjacent sibling box
above, etc. Iterating until we hit the first non-empty in-flow block.

This pulls up the bottom part of the face on ACID2. :^)
This commit is contained in:
Andreas Kling 2020-06-28 10:51:11 +02:00
parent e50fa413cb
commit 9576f6b1d4
Notes: sideshowbarker 2024-07-19 05:20:44 +09:00
1 changed files with 14 additions and 10 deletions
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24
Libraries/LibWeb/Layout/LayoutBlock.cpp
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@ -625,30 +625,34 @@ void LayoutBlock::place_block_level_non_replaced_element_in_normal_flow(LayoutBl
float y = box.margin_box(*this).top
+ box.offset.top.to_px(*this);
// NOTE: Empty (0-height) preceding siblings have their margins collapsed with *their* preceding sibling, etc.
float collapsed_bottom_margin_of_preceding_siblings = 0;
auto* relevant_sibling = block.previous_sibling();
while (relevant_sibling != nullptr) {
if (!relevant_sibling->is_absolutely_positioned() && !relevant_sibling->is_floating())
break;
if (!relevant_sibling->is_absolutely_positioned() && !relevant_sibling->is_floating()) {
collapsed_bottom_margin_of_preceding_siblings = max(collapsed_bottom_margin_of_preceding_siblings, relevant_sibling->box_model().margin.bottom.to_px(*relevant_sibling));
if (relevant_sibling->height() > 0)
break;
}
relevant_sibling = relevant_sibling->previous_sibling();
}
if (relevant_sibling) {
auto& sibling_box = relevant_sibling->box_model();
y += relevant_sibling->effective_offset().y() + relevant_sibling->height();
// Collapse top margin with bottom margin of previous sibling if necessary
float previous_sibling_margin_bottom = sibling_box.margin.bottom.to_px(*relevant_sibling);
// Collapse top margin with bottom margin of preceding siblings if needed
float my_margin_top = box.margin.top.to_px(*this);
if (my_margin_top < 0 || previous_sibling_margin_bottom < 0) {
if (my_margin_top < 0 || collapsed_bottom_margin_of_preceding_siblings < 0) {
// Negative margins present.
float largest_negative_margin = -min(my_margin_top, previous_sibling_margin_bottom);
float largest_positive_margin = (my_margin_top < 0 && previous_sibling_margin_bottom < 0) ? 0 : max(my_margin_top, previous_sibling_margin_bottom);
float largest_negative_margin = -min(my_margin_top, collapsed_bottom_margin_of_preceding_siblings);
float largest_positive_margin = (my_margin_top < 0 && collapsed_bottom_margin_of_preceding_siblings < 0) ? 0 : max(my_margin_top, collapsed_bottom_margin_of_preceding_siblings);
float final_margin = largest_positive_margin - largest_negative_margin;
y += final_margin - my_margin_top;
} else if (previous_sibling_margin_bottom > my_margin_top) {
} else if (collapsed_bottom_margin_of_preceding_siblings > my_margin_top) {
// Sibling's margin is larger than mine, adjust so we use sibling's.
y += previous_sibling_margin_bottom - my_margin_top;
y += collapsed_bottom_margin_of_preceding_siblings - my_margin_top;
}
}