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LibWeb: Fix and improve float positioning behavior

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Our recent change to get rid of the "move 1px at a time" algorithm in
the float positioning logic introduced the issue that potentially
intersecting float boxes were not evaluated in order anymore. This could
result in float boxes being pushed down further than strictly necessary.

By finding the highest point we can move the floating box to and
repeating the process until we're no longer intersecting any floating
box, we also solve some edge cases like intersecting with very long
floating boxes whose edges lay outside the current box' edges.

This is by no means the most efficient solution, but it is more correct
than what we had until now.

Fixes #4110.
This commit is contained in:
Jelle Raaijmakers 2025-03-27 00:16:02 +00:00
commit c4bb74f40b
Notes: github-actions[bot] 2025-03-27 10:57:05 +00:00
5 changed files with 143 additions and 16 deletions
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53
Libraries/LibWeb/Layout/LineBuilder.cpp
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@ -129,23 +129,44 @@ CSSPixels LineBuilder::y_for_float_to_be_inserted_here(Box const& box)
// Then, look for the next Y position where we can fit the new float.
auto box_in_root_rect = m_context.parent().content_box_rect_in_ancestor_coordinate_space(box_state, m_context.parent().root());
m_context.parent().for_each_floating_box([&](auto const& float_box) {
auto candidate_block_offset_in_root = box_in_root_rect.y() + candidate_block_offset;
if (float_box.margin_box_rect_in_root_coordinate_space.bottom() < candidate_block_offset_in_root)
HashMap<CSSPixels, AvailableSize> available_space_cache;
for (;;) {
Optional<CSSPixels> highest_intersection_bottom;
auto candidate_block_top_in_root = box_in_root_rect.y() + candidate_block_offset;
auto candidate_block_bottom_in_root = candidate_block_top_in_root + height;
m_context.parent().for_each_floating_box([&](auto const& float_box) {
auto float_box_top = float_box.margin_box_rect_in_root_coordinate_space.top();
auto float_box_bottom = float_box.margin_box_rect_in_root_coordinate_space.bottom();
if (float_box_bottom <= candidate_block_top_in_root)
return IterationDecision::Continue;
auto intersection_test = [&](auto y_coordinate, auto top, auto bottom) {
if (y_coordinate < top || y_coordinate > bottom)
return;
auto available_space = available_space_cache.ensure(y_coordinate, [&]() {
return m_context.available_space_for_line(y_coordinate);
});
if (width > available_space) {
auto bottom_relative = float_box_bottom - box_in_root_rect.y();
highest_intersection_bottom = min(highest_intersection_bottom.value_or(bottom_relative), bottom_relative);
}
};
intersection_test(float_box_top, candidate_block_top_in_root, candidate_block_bottom_in_root);
intersection_test(float_box_bottom, candidate_block_top_in_root, candidate_block_bottom_in_root);
intersection_test(candidate_block_top_in_root, float_box_top, float_box_bottom);
intersection_test(candidate_block_bottom_in_root, float_box_top, float_box_bottom);
return IterationDecision::Continue;
auto space_at_y_top = m_context.available_space_for_line(candidate_block_offset);
auto space_at_y_bottom = m_context.available_space_for_line(candidate_block_offset + height);
if (width > space_at_y_top || width > space_at_y_bottom) {
if (!m_context.any_floats_intrude_at_block_offset(candidate_block_offset) && !m_context.any_floats_intrude_at_block_offset(candidate_block_offset + height)) {
return IterationDecision::Break;
}
} else {
return IterationDecision::Break;
}
// candidate_block_offset needs to stay relative to the current box
candidate_block_offset = float_box.margin_box_rect_in_root_coordinate_space.bottom() - box_in_root_rect.y();
return IterationDecision::Continue;
});
});
if (!highest_intersection_bottom.has_value() || highest_intersection_bottom.value() == candidate_block_offset)
break;
candidate_block_offset = highest_intersection_bottom.value();
}
return candidate_block_offset;
}