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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_BASELINE_UTILS_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_BASELINE_UTILS_H_
#include "third_party/blink/renderer/platform/text/writing_direction_mode.h"
namespace blink {
enum class BaselineGroup { kMajor, kMinor };
// Determines the writing-mode to read a baseline from a fragment.
inline WritingMode DetermineBaselineWritingMode(
const WritingDirectionMode container_writing_direction,
const WritingMode child_writing_mode,
bool is_parallel_context) {
// From: https://drafts.csswg.org/css-align-3/#generate-baselines
//
// For a parallel alignment context:
// "If the box establishing the alignment context has a block flow
// direction that is orthogonal to the axis of the alignment context, use
// its writing mode."
//
// Non-parallel:
// "If the child's writing-mode isn't parallel to the alignment context use
// either "horizontal-tb" or "vertical-lr" whichever is orthogonal."
const auto orthogonal_writing_mode =
(is_parallel_context)
? container_writing_direction.GetWritingMode()
: ((child_writing_mode == WritingMode::kHorizontalTb)
? (container_writing_direction.IsLtr()
? WritingMode::kVerticalLr
: WritingMode::kVerticalRl)
: WritingMode::kHorizontalTb);
const bool is_parallel = IsParallelWritingMode(
container_writing_direction.GetWritingMode(), child_writing_mode);
if (is_parallel_context)
return is_parallel ? child_writing_mode : orthogonal_writing_mode;
else
return is_parallel ? orthogonal_writing_mode : child_writing_mode;
}
// There are potentially two different baseline groups for a column/row.
// See: https://www.w3.org/TR/css-align-3/#baseline-sharing-group
//
// We label these "major"/"minor" to separate them. The "major" group should be
// aligned to the appropriate "start" axis.
inline BaselineGroup DetermineBaselineGroup(
const WritingDirectionMode container_writing_direction,
const WritingMode baseline_writing_mode,
bool is_parallel_context,
bool is_last_baseline,
bool is_flipped = false) {
const auto container_writing_mode =
container_writing_direction.GetWritingMode();
auto start_group = BaselineGroup::kMajor;
auto end_group = BaselineGroup::kMinor;
if (is_last_baseline)
std::swap(start_group, end_group);
if (is_flipped)
std::swap(start_group, end_group);
if (is_parallel_context) {
DCHECK(
IsParallelWritingMode(container_writing_mode, baseline_writing_mode));
return (baseline_writing_mode == container_writing_mode) ? start_group
: end_group;
}
// For each writing-mode the "major" group is aligned with the container's
// direction. This is to ensure the inline-start offset (for the grid-item)
// matches the baseline offset we calculate.
bool is_ltr = container_writing_direction.IsLtr();
switch (baseline_writing_mode) {
case WritingMode::kHorizontalTb:
case WritingMode::kVerticalLr:
case WritingMode::kSidewaysLr:
return is_ltr ? start_group : end_group;
case WritingMode::kVerticalRl:
case WritingMode::kSidewaysRl:
return is_ltr ? end_group : start_group;
}
NOTREACHED();
}
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_BASELINE_UTILS_H_
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