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LibWeb: Handle negative values when collapsing vertical margins

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In the presence of negative margins, we subtract the largest negative
margin from max(0, largest positive margin).
This commit is contained in:
Andreas Kling 2020-06-12 18:09:40 +02:00
parent 21b1f1653d
commit c91981eba8
3 changed files with 32 additions and 1 deletions
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9
Libraries/LibWeb/Layout/LayoutBlock.cpp
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@ -481,7 +481,14 @@ void LayoutBlock::compute_position()
// Collapse top margin with bottom margin of previous sibling if necessary
float previous_sibling_margin_bottom = previous_sibling_style.margin().bottom.to_px(*relevant_sibling);
float my_margin_top = box_model().margin().top.to_px(*this);
if (previous_sibling_margin_bottom > my_margin_top) {
if (my_margin_top < 0 || previous_sibling_margin_bottom < 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 final_margin = largest_positive_margin - largest_negative_margin;
position_y += final_margin - my_margin_top;
} else if (previous_sibling_margin_bottom > my_margin_top) {
// Sibling's margin is larger than mine, adjust so we use sibling's.
position_y += previous_sibling_margin_bottom - my_margin_top;
}