1/*
2 * Copyright (C) 2018 Igalia S.L. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23 * THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28#include "GridLayoutFunctions.h"
29#include "RenderStyleConstants.h"
30#include "WritingMode.h"
31#include <wtf/HashMap.h>
32#include <wtf/HashSet.h>
33
34namespace WebCore {
35
36// These classes are used to implement the Baseline Alignment logic, as described in the CSS Box Alignment
37// specification.
38// https://drafts.csswg.org/css-align/#baseline-terms
39//
40// A baseline-sharing group is composed of boxes that participate in baseline alignment together. This is
41// possible only if they:
42//
43// * Share an alignment context along an axis perpendicular to their baseline alignment axis.
44// * Have compatible baseline alignment preferences (i.e., the baselines that want to align are on the same
45// side of the alignment context).
46//
47// Once the BaselineGroup is instantiated, defined by a 'block-direction' (WritingMode) and a 'baseline-preference'
48// (first/last baseline), it's ready to collect the items that will participate in the Baseline Alignment logic.
49//
50class BaselineGroup {
51public:
52 // It stores an item (if not already present) and update the max_ascent and max_descent associated to this
53 // baseline-sharing group.
54 void update(const RenderBox&, LayoutUnit ascent, LayoutUnit descent);
55 LayoutUnit maxAscent() const { return m_maxAscent; }
56 LayoutUnit maxDescent() const { return m_maxDescent; }
57 int size() const { return m_items.size(); }
58
59private:
60 friend class BaselineContext;
61 BaselineGroup(WritingMode blockFlow, ItemPosition childPreference);
62
63 // Determines whether a baseline-sharing group is compatible with an item, based on its 'block-flow' and
64 // 'baseline-preference'
65 bool isCompatible(WritingMode, ItemPosition) const;
66
67 // Determines whether the baseline-sharing group's associated block-flow is opposite (LR vs RL) to particular
68 // item's writing-mode.
69 bool isOppositeBlockFlow(WritingMode blockFlow) const;
70
71 // Determines whether the baseline-sharing group's associated block-flow is orthogonal (vertical vs horizontal)
72 // to particular item's writing-mode.
73 bool isOrthogonalBlockFlow(WritingMode blockFlow) const;
74
75 WritingMode m_blockFlow;
76 ItemPosition m_preference;
77 LayoutUnit m_maxAscent;
78 LayoutUnit m_maxDescent;
79 HashSet<const RenderBox*> m_items;
80};
81
82// https://drafts.csswg.org/css-align-3/#shared-alignment-context
83// Boxes share an alignment context along a particular axis when they are:
84//
85// * table cells in the same row, along the table's row (inline) axis
86// * table cells in the same column, along the table's column (block) axis
87// * grid items in the same row, along the grid's row (inline) axis
88// * grid items in the same column, along the grid's colum (block) axis
89// * flex items in the same flex line, along the flex container's main axis
90//
91// https://drafts.csswg.org/css-align-3/#baseline-sharing-group
92// A Baseline alignment-context may handle several baseline-sharing groups. In order to create an instance, we
93// need to pass the required data to define the first baseline-sharing group; a Baseline Context must have at
94// least one baseline-sharing group.
95//
96// By adding new items to a Baseline Context, the baseline-sharing groups it handles are automatically updated,
97// if there is one that is compatible with such item. Otherwise, a new baseline-sharing group is created,
98// compatible with the new item.
99class BaselineContext {
100 WTF_MAKE_FAST_ALLOCATED;
101public:
102 BaselineContext(const RenderBox& child, ItemPosition preference, LayoutUnit ascent, LayoutUnit descent);
103 const BaselineGroup& sharedGroup(const RenderBox& child, ItemPosition preference) const;
104
105 // Updates the baseline-sharing group compatible with the item.
106 // We pass the item's baseline-preference to avoid dependencies with the LayoutGrid class, which is the one
107 // managing the alignment behavior of the Grid Items.
108 void updateSharedGroup(const RenderBox& child, ItemPosition preference, LayoutUnit ascent, LayoutUnit descent);
109
110private:
111 // Returns the baseline-sharing group compatible with an item.
112 // We pass the item's baseline-preference to avoid dependencies with the LayoutGrid class, which is the one
113 // managing the alignment behavior of the Grid Items.
114 // FIXME: Properly implement baseline-group compatibility.
115 // See https://github.com/w3c/csswg-drafts/issues/721
116 BaselineGroup& findCompatibleSharedGroup(const RenderBox& child, ItemPosition preference);
117
118 Vector<BaselineGroup> m_sharedGroups;
119};
120
121static inline bool isBaselinePosition(ItemPosition position)
122{
123 return position == ItemPosition::Baseline || position == ItemPosition::LastBaseline;
124}
125
126// This is the class that implements the Baseline Alignment logic, using internally the BaselineContext and
127// BaselineGroupd classes (described above).
128//
129// The first phase is to collect the items that will participate in baseline alignment together. During this
130// phase the required baseline-sharing groups will be created for each Baseline alignment-context shared by
131// the items participating in the baseline alignment.
132//
133// Additionally, the baseline-sharing groups' offsets, max-ascend and max-descent will be computed and stored.
134// This class also computes the baseline offset for a particular item, based on the max-ascent for its associated
135// baseline-sharing group.
136class GridBaselineAlignment {
137public:
138 // Collects the items participating in baseline alignment and updates the corresponding baseline-sharing
139 // group of the Baseline Context the items belongs to.
140 // All the baseline offsets are updated accordingly based on the added item.
141 void updateBaselineAlignmentContext(ItemPosition, unsigned sharedContext, const RenderBox&, GridAxis);
142
143 // Returns the baseline offset of a particular item, based on the max-ascent for its associated
144 // baseline-sharing group
145 LayoutUnit baselineOffsetForChild(ItemPosition, unsigned sharedContext, const RenderBox&, GridAxis) const;
146
147 // Sets the Grid Container's writing-mode so that we can avoid the dependecy of the LayoutGrid class for
148 // determining whether a grid item is orthogonal or not.
149 void setBlockFlow(WritingMode blockFlow) { m_blockFlow = blockFlow; };
150
151 // Clearing the Baseline Alignment context and their internal classes and data structures.
152 void clear(GridAxis);
153
154private:
155 const BaselineGroup& baselineGroupForChild(ItemPosition, unsigned sharedContext, const RenderBox&, GridAxis) const;
156 LayoutUnit marginOverForChild(const RenderBox&, GridAxis) const;
157 LayoutUnit marginUnderForChild(const RenderBox&, GridAxis) const;
158 LayoutUnit logicalAscentForChild(const RenderBox&, GridAxis) const;
159 LayoutUnit ascentForChild(const RenderBox&, GridAxis) const;
160 LayoutUnit descentForChild(const RenderBox&, LayoutUnit, GridAxis) const;
161 bool isDescentBaselineForChild(const RenderBox&, GridAxis) const;
162 bool isHorizontalBaselineAxis(GridAxis) const;
163 bool isOrthogonalChildForBaseline(const RenderBox&) const;
164 bool isParallelToBaselineAxisForChild(const RenderBox&, GridAxis) const;
165
166 typedef HashMap<unsigned, std::unique_ptr<BaselineContext>, DefaultHash<unsigned>::Hash, WTF::UnsignedWithZeroKeyHashTraits<unsigned>> BaselineContextsMap;
167
168 // Grid Container's WritingMode, used to determine grid item's orthogonality.
169 WritingMode m_blockFlow;
170 BaselineContextsMap m_rowAxisAlignmentContext;
171 BaselineContextsMap m_colAxisAlignmentContext;
172};
173
174} // namespace WebCore
175