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LibWeb: Refactor text justification code + only justify below threshold

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All the justification-related code is now in
InlineFormattingContext::apply_justification_to_fragments and is
performed after all the line boxes have been added.

Text justification now only happens on the last line if the excess space
including whitespace is below a certain threshold. 10% seemed reasonable
since it prevents the "over-justification" of text. Note that fragments
in line boxes before the last one are always justified.
This commit is contained in:
sin-ack 2022-03-12 17:01:06 +00:00 • committed by Andreas Kling
parent f0a1ab6f84
commit 7fe3f2d970
3 changed files with 53 additions and 26 deletions
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52
Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp
View file

@ -17,6 +17,8 @@
namespace Web::Layout {
constexpr float text_justification_threshold = 0.1;
InlineFormattingContext::InlineFormattingContext(FormattingState& state, BlockContainer const& containing_block, BlockFormattingContext& parent)
: FormattingContext(Type::Inline, state, containing_block, &parent)
{
@ -164,6 +166,45 @@ void InlineFormattingContext::dimension_box_on_line(Box const& box, LayoutMode l
dump_tree(box);
}
void InlineFormattingContext::apply_justification_to_fragments(FormattingState::NodeState const& containing_block_state, LineBox& line_box, bool is_last_line)
{
float excess_horizontal_space = containing_block_state.content_width - line_box.width();
// Only justify the text if the excess horizontal space is less than or
// equal to 10%, or if we are not looking at the last line box.
if (is_last_line && excess_horizontal_space / containing_block_state.content_width > text_justification_threshold)
return;
float excess_horizontal_space_including_whitespace = excess_horizontal_space;
size_t whitespace_count = 0;
for (auto& fragment : line_box.fragments()) {
if (fragment.is_justifiable_whitespace()) {
++whitespace_count;
excess_horizontal_space_including_whitespace += fragment.width();
}
}
float justified_space_width = whitespace_count > 0 ? (excess_horizontal_space_including_whitespace / static_cast<float>(whitespace_count)) : 0;
// This is the amount that each fragment will be offset by. If a whitespace
// fragment is shorter than the justified space width, it increases to push
// subsequent fragments, and decreases to pull them back otherwise.
float running_diff = 0;
for (size_t i = 0; i < line_box.fragments().size(); ++i) {
auto& fragment = line_box.fragments()[i];
auto offset = fragment.offset();
offset.translate_by(running_diff, 0);
fragment.set_offset(offset);
if (fragment.is_justifiable_whitespace()
&& fragment.width() != justified_space_width) {
running_diff += justified_space_width - fragment.width();
fragment.set_width(justified_space_width);
}
}
}
void InlineFormattingContext::generate_line_boxes(LayoutMode layout_mode)
{
auto& containing_block_state = m_state.get_mutable(containing_block());
@ -221,6 +262,17 @@ void InlineFormattingContext::generate_line_boxes(LayoutMode layout_mode)
}
line_builder.remove_last_line_if_empty();
auto const& containing_block = this->containing_block();
auto text_align = containing_block.computed_values().text_align();
if (text_align == CSS::TextAlign::Justify) {
auto const& containing_block_state = m_state.get(containing_block);
for (size_t i = 0; i < line_boxes.size(); i++) {
auto& line_box = line_boxes[i];
auto is_last_line = i == line_boxes.size() - 1;
apply_justification_to_fragments(containing_block_state, line_box, is_last_line);
}
}
}
}