layout_box_model_object.h | Explore in Territory

/*
 * Copyright (C) 1999 Lars Knoll ([email protected])
 *           (C) 1999 Antti Koivisto ([email protected])
 * Copyright (C) 2003, 2006, 2007, 2009 Apple Inc. All rights reserved.
 * Copyright (C) 2010 Google Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_LAYOUT_BOX_MODEL_OBJECT_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_LAYOUT_BOX_MODEL_OBJECT_H_

#include "base/notreached.h"
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/layout/background_bleed_avoidance.h"
#include "third_party/blink/renderer/core/layout/content_change_type.h"
#include "third_party/blink/renderer/core/layout/layout_object.h"
#include "third_party/blink/renderer/platform/text/writing_mode_utils.h"

namespace blink {

class PaintLayer;
class PaintLayerScrollableArea;
struct LogicalRect;

enum PaintLayerType { … };

// This class is the base class for all CSS objects.
//
// All CSS objects follow the box model object. See THE BOX MODEL section in
// LayoutBox for more information.
//
// This class actually doesn't have the box model but it exposes some common
// functions or concepts that sub-classes can extend upon. For example, there
// are accessors for margins, borders, paddings and borderBoundingBox().
//
// The reason for this partial implementation is that the 2 classes inheriting
// from it (LayoutBox and LayoutInline) have different requirements but need to
// have a PaintLayer. For a full implementation of the box model, see LayoutBox.
//
// An important member of this class is PaintLayer, which is stored in a rare-
// data pattern (see: Layer()). PaintLayers are instantiated for several reasons
// based on the return value of layerTypeRequired().
// Interestingly, most SVG objects inherit from LayoutSVGModelObject and thus
// can't have a PaintLayer. This is an unfortunate artifact of our
// design as it limits code sharing and prevents hardware accelerating SVG
// (the current design require a PaintLayer for compositing).
//
//
// ***** COORDINATE SYSTEMS *****
//
// In order to fully understand LayoutBoxModelObject and the inherited classes,
// we need to introduce the concept of coordinate systems.
// There are 4 coordinate systems:
// - physical coordinates: it is the coordinate system used for painting and
//   correspond to physical direction as seen on the physical display (screen,
//   printed page). In CSS, 'top', 'right', 'bottom', 'left' are all in physical
//   coordinates. The code matches this convention too.
//
// - logical coordinates: this is the coordinate system used for layout. It is
//   determined by 'writing-mode' and 'direction'. Any property using 'before',
//   'after', 'start' or 'end' is in logical coordinates. Those are also named
//   respectively 'logical top', 'logical bottom', 'logical left' and
//   'logical right'.
//
// Example with writing-mode: vertical-rl; direction: ltr;
//
//                    'top' / 'start' side
//
//                     block-flow direction
//           <------------------------------------ |
//           ------------------------------------- |
//           |        c   |          s           | |
// 'left'    |        o   |          o           | |   inline     'right'
//    /      |        n   |          m           | |  direction      /
// 'after'   |        t   |          e           | |              'before'
//  side     |        e   |                      | |                side
//           |        n   |                      | |
//           |        t   |                      | |
//           ------------------------------------- v
//
//                 'bottom' / 'end' side
//
// See https://drafts.csswg.org/css-writing-modes-3/#text-flow for some
// extra details.
//
// - physical coordinates with flipped block-flow direction: those are physical
//   coordinates but we flipped the block direction. Almost all geometries
//   in box layout use this coordinate space, except those having explicit
//   "Logical" or "Physical" prefix in their names, or the name implies logical
//   (e.g. InlineStart, BlockEnd) or physical (e.g. Top, Left), or the return
//   type is PhysicalRect.
//
// - logical coordinates without flipping inline direction: those are "logical
//   block coordinates", without considering text direction. Examples are
//   "LogicalLeft" and "LogicalRight".
//
// For more information, see the following doc about coordinate spaces:
// https://chromium.googlesource.com/chromium/src.git/+/main/third_party/blink/renderer/core/layout/README.md#coordinate-spaces
class CORE_EXPORT LayoutBoxModelObject : public LayoutObject { … };

template <>
struct DowncastTraits<LayoutBoxModelObject> { … };

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_LAYOUT_BOX_MODEL_OBJECT_H_
chromium/third_party/blink/renderer/core/layout/layout_box_model_object.h
