diff --git a/Base/res/html/misc/margin-collapse-3.html b/Base/res/html/misc/margin-collapse-3.html
new file mode 100644
index 0000000000..84be5b05a7
--- /dev/null
+++ b/Base/res/html/misc/margin-collapse-3.html
@@ -0,0 +1,22 @@
+
+
+
diff --git a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
index 5b51cd3574..1a09a04686 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
+++ b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
@@ -372,7 +372,8 @@ void BlockFormattingContext::layout_block_level_box(Box const& box, BlockContain
return;
if (box.is_floating()) {
- layout_floating_box(box, block_container, layout_mode, available_space, m_margin_state.current_collapsed_margin() + current_y);
+ auto margin_top = !m_margin_state.has_block_container_waiting_for_final_y_position() ? m_margin_state.current_collapsed_margin() : 0;
+ layout_floating_box(box, block_container, layout_mode, available_space, margin_top + current_y);
bottom_of_lowest_margin_box = max(bottom_of_lowest_margin_box, box_state.offset.y() + box_state.content_height() + box_state.margin_box_bottom());
return;
}
@@ -383,8 +384,18 @@ void BlockFormattingContext::layout_block_level_box(Box const& box, BlockContain
compute_height(box, available_space);
}
+ if (box.computed_values().clear() != CSS::Clear::None) {
+ m_margin_state.reset();
+ }
+
m_margin_state.add_margin(box_state.margin_top);
+ m_margin_state.update_block_waiting_for_final_y_position();
+
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;
+ }
place_block_level_element_in_normal_flow_vertically(box, current_y + box_state.border_box_top() + margin_top);
place_block_level_element_in_normal_flow_horizontally(box, available_space);
@@ -401,7 +412,16 @@ void BlockFormattingContext::layout_block_level_box(Box const& box, BlockContain
if (box.children_are_inline()) {
layout_inline_children(verify_cast(box), layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
} else {
- m_margin_state.reset();
+ 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([&](float margin_top) {
+ place_block_level_element_in_normal_flow_vertically(box, margin_top + current_y + box_state.border_box_top());
+ });
+ }
+
layout_block_level_children(verify_cast(box), layout_mode, box_state.available_inner_space_or_constraints_from(available_space));
}
}
@@ -415,6 +435,7 @@ void BlockFormattingContext::layout_block_level_box(Box const& box, BlockContain
}
m_margin_state.add_margin(box_state.margin_bottom);
+ m_margin_state.update_block_waiting_for_final_y_position();
compute_inset(box);
@@ -440,7 +461,11 @@ void BlockFormattingContext::layout_block_level_children(BlockContainer const& b
return IterationDecision::Continue;
});
- // FIXME: margin-bottom of last in-flow child can be collapsed with margin-bottom of parent
+ // FIXME: The bottom margin of an in-flow block box with a 'height' of 'auto' collapses with its last in-flow block-level child's bottom margin, if:
+ // the box has no bottom padding, and
+ // the box has no bottom border, and
+ // the child's bottom margin neither collapses with a top margin that has clearance, nor (if the box's min-height is non-zero) with the box's top margin.
+ // https://www.w3.org/TR/CSS22/box.html#collapsing-margins
m_margin_state.reset();
if (layout_mode == LayoutMode::IntrinsicSizing) {
diff --git a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h
index a896cb4966..32d5524137 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h
+++ b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h
@@ -113,16 +113,36 @@ private:
struct BlockMarginState {
Vector current_collapsible_margins;
+ Function block_container_y_position_update_callback;
void add_margin(float margin)
{
current_collapsible_margins.append(margin);
}
+ void register_block_container_y_position_update_callback(Function callback)
+ {
+ block_container_y_position_update_callback = move(callback);
+ }
+
float current_collapsed_margin() const;
+ bool has_block_container_waiting_for_final_y_position() const
+ {
+ return static_cast(block_container_y_position_update_callback);
+ }
+
+ void update_block_waiting_for_final_y_position() const
+ {
+ if (block_container_y_position_update_callback) {
+ float collapsed_margin = current_collapsed_margin();
+ block_container_y_position_update_callback(collapsed_margin);
+ }
+ }
+
void reset()
{
+ block_container_y_position_update_callback = {};
current_collapsible_margins.clear();
}
};