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* Copyright 2015 Google Inc. All Rights Reserved.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <vector>
#include "base/memory/ref_counted.h"
#include "base/optional.h"
#include "cobalt/layout/base_direction.h"
#include "cobalt/layout/box.h"
#include "cobalt/layout/layout_unit.h"
#include "cobalt/render_tree/font.h"
namespace cobalt {
namespace layout {
// The rectangular area that contains the boxes that form a line is called
// a line box.
// Note that the line box is not an actual box. To maintain consistency, we
// follow the nomenclature of CSS 2.1 specification. But we do not derive
// |LineBox| from |Box| because, despite the name, a line box is much closer
// to block and inline formatting contexts than to a box.
// A line box is a short-lived object that is constructed and destroyed during
// the layout. It does not own child boxes nor trigger their layout, which is a
// responsibility of the box that establishes this formatting context. This
// class merely knows how to determine which children to include on the line,
// where to wrap those children, and how to calculate the positions of those
// children.
// Due to bidirectional reordering and the horizontal and vertical alignment,
// used values of "left" and "top" can only be calculated when the line ends. To
// ensure that the line box has completed all calculations, |EndUpdates| must be
// called.
class LineBox {
LineBox(LayoutUnit top, bool position_children_relative_to_baseline,
const scoped_refptr<cssom::PropertyValue>& line_height,
const render_tree::FontMetrics& font_metrics,
bool should_collapse_leading_white_space,
bool should_collapse_trailing_white_space,
const LayoutParams& layout_params, BaseDirection base_direction,
const scoped_refptr<cssom::PropertyValue>& text_align,
const scoped_refptr<cssom::PropertyValue>& font_size,
LayoutUnit indent_offset, LayoutUnit ellipsis_width);
LayoutUnit top() const { return top_; }
// Attempt to add the child box to the line, which may cause a line wrap to
// occur if the box overflows the line and a usable wrap location is available
// among the child boxes. When this occurs, a box is returned. This signifies
// the last child box included on the line before the wrap and can be the
// current child box or any previously added one. All boxes that were
// previously added after the returned box must be re-inserted, as they were
// not successfully placed on the line.
// The returned box can potentially be split as a result of the line wrap, in
// which case, the portion after the split will be accessible via the child
// box's |GetSplitSibling| call. This split sibling should be the first box
// added the next time |TryAddChildAndMaybeWrap| is called, followed by any
// additional child boxes that were not placed on the line.
// This call asynchronously calculates the positions and sizes of the added
// child boxes. The used values will be undefined until |EndUpdates| is
// called.
Box* TryAddChildAndMaybeWrap(Box* child_box);
// Asynchronously adds the given child box to the line, ignoring any possible
// overflow. The used values will be undefined until |EndUpdates| is called.
void BeginAddChildAndMaybeOverflow(Box* child_box);
// Ensures that the calculation of used values for all previously seen child
// boxes is completed.
void EndUpdates();
// WARNING: All public methods below may be called only after |EndUpdates|.
// Whether the line starts with a white space.
bool HasLeadingWhiteSpace() const;
// Whether the line ends with a white space.
bool HasTrailingWhiteSpace() const;
// Whether all boxes on the line are collapsed.
bool IsCollapsed() const;
// Line boxes that contain no text, no preserved white space, no inline
// elements with non-zero margins, padding, or borders, and no other in-flow
// content must be treated as zero-height line boxes for the purposes
// of determining the positions of any elements inside of them, and must be
// treated as not existing for any other purpose.
bool LineExists() const;
// Returns the first box justifing the line's existence.
// NOTE: This includes absolutely positioned children.
size_t GetFirstBoxJustifyingLineExistenceIndex() const;
bool IsEllipsisPlaced() const;
math::Vector2dF GetEllipsisCoordinates() const;
// Used to calculate the width of an inline container box.
LayoutUnit shrink_to_fit_width() const { return shrink_to_fit_width_; }
// Used to calculate the "auto" height of the box that establishes this
// formatting context.
LayoutUnit height() const { return height_; }
// Returns the vertical offset of the baseline from the top of the line box.
// May return non-zero values even for empty line boxes, because of the strut.
LayoutUnit baseline_offset_from_top() const {
return baseline_offset_from_top_;
enum HorizontalAlignment {
LayoutUnit GetAvailableWidth() const;
void UpdateSizePreservingTrailingWhiteSpace(Box* child_box);
bool ShouldCollapseLeadingWhiteSpaceInNextChildBox() const;
void CollapseTrailingWhiteSpace();
void RestoreTrailingWhiteSpace();
bool TryAddChildWithinAvailableWidth(Box* child_box);
bool TryWrapOverflowingBoxAndMaybeAddSplitChild(
WrapAtPolicy wrap_at_policy,
WrapOpportunityPolicy wrap_opportunity_policy, Box* child_box);
bool TryWrapChildrenAtLastOpportunity(
WrapOpportunityPolicy wrap_opportunity_policy);
// Asynchronously estimates the static position of the given child box.
// In CSS 2.1 the static position is only defined for absolutely positioned
// boxes. The used values will be undefined until |EndUpdates| is called.
void BeginEstimateStaticPositionForAbsolutelyPositionedChild(Box* child_box);
void BeginAddChildInternal(Box* child_box);
void ReverseChildBoxesByBidiLevels();
void ReverseChildBoxesMeetingBidiLevelThreshold(int level);
void UpdateChildBoxLeftPositions();
void SetLineBoxHeightFromChildBoxes();
void UpdateChildBoxTopPositions();
void MaybePlaceEllipsis();
LayoutUnit GetHeightAboveMiddleAlignmentPoint(Box* child_box);
HorizontalAlignment ComputeHorizontalAlignment() const;
const LayoutUnit top_;
const bool position_children_relative_to_baseline_;
const scoped_refptr<cssom::PropertyValue> line_height_;
const render_tree::FontMetrics font_metrics_;
const bool should_collapse_leading_white_space_;
const bool should_collapse_trailing_white_space_;
const LayoutParams layout_params_;
const BaseDirection base_direction_;
const scoped_refptr<cssom::PropertyValue> text_align_;
const scoped_refptr<cssom::PropertyValue> font_size_;
const LayoutUnit indent_offset_;
const LayoutUnit ellipsis_width_;
bool has_overflowed_;
bool at_end_;
// Non-owned list of child boxes.
// Horizontal and vertical alignments make it impossible to calculate
// positions of children before all children are known.
typedef std::vector<Box*> ChildBoxes;
ChildBoxes child_boxes_;
int num_absolutely_positioned_boxes_before_first_box_justifying_line_;
// Accessing boxes indicated by these indices are only valid before
// EndUpdates() is called, because the positions of the boxes may change
// during bidirectional sorting.
base::optional<size_t> first_box_justifying_line_existence_index_;
base::optional<size_t> first_non_collapsed_child_box_index_;
base::optional<size_t> last_non_collapsed_child_box_index_;
// These flags are set when EndUpdates() is called. This allows the leading
// and trailing white space state of the line to be accessible even after
// the boxes have been moved as a result of bidirectional sorting.
base::optional<bool> has_leading_white_space_;
base::optional<bool> has_trailing_white_space_;
LayoutUnit shrink_to_fit_width_;
LayoutUnit height_;
LayoutUnit baseline_offset_from_top_;
bool is_ellipsis_placed_;
LayoutUnit placed_ellipsis_offset_;
} // namespace layout
} // namespace cobalt