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/*
* Copyright (C) 2023 Apple Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include "LayoutUnit.h"
#include "RenderStyleConstants.h"
#include "WritingMode.h"
#include <wtf/TZoneMalloc.h>
#include <wtf/WeakHashSet.h>
namespace WebCore {
class RenderBox;
// These classes are used to implement the Baseline Alignment logic, as described in the CSS Box Alignment
// specification.
// https://drafts.csswg.org/css-align/#baseline-terms
//
// A baseline-sharing group is composed of boxes that participate in baseline alignment together. This is
// possible only if they:
//
// * Share an alignment context along an axis perpendicular to their baseline alignment axis.
// * Have compatible baseline alignment preferences (i.e., the baselines that want to align are on the same
// side of the alignment context).
//
// Once the BaselineGroup is instantiated, defined by a 'block flow direction' and a 'baseline-preference'
// (first/last baseline), it's ready to collect the items that will participate in the Baseline Alignment logic.
//
class BaselineGroup {
WTF_MAKE_TZONE_ALLOCATED(BaselineGroup);
public:
// It stores an item (if not already present) and update the max_ascent associated to this
// baseline-sharing group.
void update(const RenderBox&, LayoutUnit ascent);
LayoutUnit maxAscent() const { return m_maxAscent; }
int computeSize() const { return m_items.computeSize(); }
auto begin() { return m_items.begin(); }
auto end() { return m_items.end(); }
private:
friend class BaselineAlignmentState;
BaselineGroup(FlowDirection, ItemPosition childPreference);
// Determines whether a baseline-sharing group is compatible with an item, based on its 'block-flow' and
// 'baseline-preference'
bool isCompatible(FlowDirection, ItemPosition) const;
// Determines whether the baseline-sharing group's associated block-flow is opposite (LR vs RL) to particular
// item's writing-mode.
bool isOppositeBlockFlow(FlowDirection) const;
// Determines whether the baseline-sharing group's associated block-flow is orthogonal (vertical vs horizontal)
// to particular item's writing-mode.
bool isOrthogonalBlockFlow(FlowDirection) const;
FlowDirection m_blockFlow;
ItemPosition m_preference;
LayoutUnit m_maxAscent;
SingleThreadWeakHashSet<RenderBox> m_items;
};
//
// BaselineAlignmentState provides an API to interact with baseline sharing groups in various
// ways such as adding items to appropriate ones and querying the baseline sharing group for
// an item. A BaselineAlignmentState should be created by a formatting context to use for each
// of its baseline alignment contexts.
//
// https://drafts.csswg.org/css-align-3/#baseline-sharing-group
// A Baseline alignment-context may handle several baseline-sharing groups. In order to create an instance, we
// need to pass the required data to define the first baseline-sharing group; a BaselineAlignmentState must have at
// least one baseline-sharing group.
//
// By adding new items to a BaselineAlignmentState, the baseline-sharing groups it handles are automatically updated,
// if there is one that is compatible with such item. Otherwise, a new baseline-sharing group is created,
// compatible with the new item.
class BaselineAlignmentState {
WTF_MAKE_TZONE_ALLOCATED(BaselineAlignmentState);
public:
BaselineAlignmentState(const RenderBox& child, ItemPosition preference, LayoutUnit ascent);
const BaselineGroup& sharedGroup(const RenderBox& child, ItemPosition preference) const;
// Updates the baseline-sharing group compatible with the item.
// We pass the item's baseline-preference to avoid dependencies with the LayoutGrid class, which is the one
// managing the alignment behavior of the Grid Items.
void updateSharedGroup(const RenderBox& child, ItemPosition preference, LayoutUnit ascent);
Vector<BaselineGroup>& sharedGroups();
private:
// Returns the baseline-sharing group compatible with an item.
// We pass the item's baseline-preference to avoid dependencies with the LayoutGrid class, which is the one
// managing the alignment behavior of the Grid Items.
// FIXME: Properly implement baseline-group compatibility.
// See https://github.com/w3c/csswg-drafts/issues/721
BaselineGroup& findCompatibleSharedGroup(const RenderBox& child, ItemPosition preference);
Vector<BaselineGroup> m_sharedGroups;
};
} // namespace WebCore
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