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LibWeb: Improve inline flow around floating boxes

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This patch combines a number of techniques to make inline content flow
more correctly around floats:

- During inline layout, BFC now lets LineBuilder decide the Y coordinate
  when inserting a new float. LineBuilder has more information about the
  currently accumulated line, and can make better breaking decisions.

- When inserting a float on one side, and the top of the newly inserted
  float is below the bottommost float on the opposite side, we now reset
  the opposite side back to the start of that edge. This improves
  breaking behavior between opposite-side floats.

- After inserting a float during inline layout, we now recalculate the
  available space on the line, but don't adjust X offsets of already
  existing fragments. This is handled by update_last_line() anyway,
  so it was pointless busywork.

- When measuring whether a line can fit at a given Y coordinate, we now
  consider both the top and bottom Y values of the line. This fixes an
  issue where the bottom part of a line would bleed over other content
  (since we had only checked that the top Y coordinate of that line
  would fit.)

There are some pretty brain-dead algorithms in here that we need to make
smarter, but I didn't want to complicate this any further so I've left
FIXMEs about them instead.
This commit is contained in:
Andreas Kling 2022-09-16 14:21:52 +02:00
parent 54e7359243
commit 412b2313f3
6 changed files with 185 additions and 32 deletions
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36
Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
View file

@ -616,17 +616,15 @@ void BlockFormattingContext::layout_floating_box(Box const& box, BlockContainer
// First we place the box normally (to get the right y coordinate.)
// If we have a LineBuilder, we're in the middle of inline layout, otherwise this is block layout.
if (line_builder) {
float y_offset = box_state.margin_box_top();
line_builder->break_if_needed(box_state.margin_box_width());
box_state.offset.set_y(line_builder->current_y() + y_offset);
line_builder->adjust_last_line_after_inserting_floating_box({}, box.computed_values().float_(), box_state.margin_box_width());
auto y = line_builder->y_for_float_to_be_inserted_here(box);
box_state.offset.set_y(y + box_state.margin_box_top());
} else {
place_block_level_element_in_normal_flow_vertically(box, containing_block);
place_block_level_element_in_normal_flow_horizontally(box, containing_block);
}
// Then we float it to the left or right.
auto float_box = [&](FloatSide side, FloatSideData& side_data) {
auto float_box = [&](FloatSide side, FloatSideData& side_data, FloatSideData& other_side_data) {
float offset_from_edge = 0;
auto float_to_edge = [&] {
if (side == FloatSide::Left)
@ -684,7 +682,15 @@ void BlockFormattingContext::layout_floating_box(Box const& box, BlockContainer
side_data.clear();
}
}
y += side_data.y_offset;
// NOTE: If we're in inline layout, the LineBuilder has already provided the right Y offset.
// In block layout, we adjust by the side's current Y offset here.
// FIXME: It's annoying that we have different behavior for inline vs block here.
// Find a way to unify the behavior so we don't need to branch here.
if (!line_builder)
y += side_data.y_offset;
side_data.all_boxes.append(adopt_own(*new FloatingBox {
.box = box,
.offset_from_edge = offset_from_edge,
@ -703,16 +709,24 @@ void BlockFormattingContext::layout_floating_box(Box const& box, BlockContainer
// NOTE: We don't set the X position here, that happens later, once we know the root block width.
// See parent_context_did_dimension_child_root_box() for that logic.
box_state.offset.set_y(y);
// If the new box was inserted below the bottom of the opposite side,
// we reset the other side back to its edge.
if (y > other_side_data.y_offset)
other_side_data.clear();
};
// Next, float to the left and/or right
if (box.computed_values().float_() == CSS::Float::Left) {
float_box(FloatSide::Left, m_left_floats);
float_box(FloatSide::Left, m_left_floats, m_right_floats);
} else if (box.computed_values().float_() == CSS::Float::Right) {
float_box(FloatSide::Right, m_right_floats);
float_box(FloatSide::Right, m_right_floats, m_left_floats);
}
m_state.get_mutable(root()).add_floating_descendant(box);
if (line_builder)
line_builder->recalculate_available_space();
}
void BlockFormattingContext::layout_list_item_marker(ListItemBox const& list_item_box)
@ -755,7 +769,8 @@ BlockFormattingContext::SpaceUsedByFloats BlockFormattingContext::space_used_by_
{
SpaceUsedByFloats space_used_by_floats;
for (auto const& floating_box : m_left_floats.current_boxes.in_reverse()) {
for (auto const& floating_box_ptr : m_left_floats.all_boxes.in_reverse()) {
auto const& floating_box = *floating_box_ptr;
auto const& floating_box_state = m_state.get(floating_box.box);
// NOTE: The floating box is *not* in the final horizontal position yet, but the size and vertical position is valid.
auto rect = border_box_rect_in_ancestor_coordinate_space(floating_box.box, root(), m_state);
@ -767,7 +782,8 @@ BlockFormattingContext::SpaceUsedByFloats BlockFormattingContext::space_used_by_
}
}
for (auto const& floating_box : m_right_floats.current_boxes.in_reverse()) {
for (auto const& floating_box_ptr : m_right_floats.all_boxes.in_reverse()) {
auto const& floating_box = *floating_box_ptr;
auto const& floating_box_state = m_state.get(floating_box.box);
// NOTE: The floating box is *not* in the final horizontal position yet, but the size and vertical position is valid.
auto rect = border_box_rect_in_ancestor_coordinate_space(floating_box.box, root(), m_state);