chromium/third_party/blink/renderer/core/paint/paint_layer_stacking_node.h

/*
 * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
 * Copyright (C) 2013 Intel Corporation. All rights reserved.
 *
 * Portions are Copyright (C) 1998 Netscape Communications Corporation.
 *
 * Other contributors:
 *   Robert O'Callahan <[email protected]>
 *   David Baron <[email protected]>
 *   Christian Biesinger <[email protected]>
 *   Randall Jesup <[email protected]>
 *   Roland Mainz <[email protected]>
 *   Josh Soref <[email protected]>
 *   Boris Zbarsky <[email protected]>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 *
 * Alternatively, the contents of this file may be used under the terms
 * of either the Mozilla Public License Version 1.1, found at
 * http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
 * License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
 * (the "GPL"), in which case the provisions of the MPL or the GPL are
 * applicable instead of those above.  If you wish to allow use of your
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 */

#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_PAINT_LAYER_STACKING_NODE_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_PAINT_LAYER_STACKING_NODE_H_

#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/layout/layout_box_model_object.h"
#include "third_party/blink/renderer/platform/heap/collection_support/heap_hash_map.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"

namespace blink {

class PaintLayer;
class ComputedStyle;

// This class is only for PaintLayer, PaintLayerPaintOrderIterator and
// PaintLayerPaintOrderReverseIterator. Other classes should not use this class.
//
// PaintLayerStackingNode represents a stacked element which is either a
// stacking context or a positioned element.
// See
// https://chromium.googlesource.com/chromium/src.git/+/main/third_party/blink/renderer/core/paint/README.md
// for more details of stacked elements.
//
// Stacked elements are the basis for the CSS painting algorithm. The paint
// order is determined by walking stacked elements in an order defined by
// ‘z-index’. This walk is interleaved with non-stacked contents.
// See CSS 2.1 appendix E for the actual algorithm
// http://www.w3.org/TR/CSS21/zindex.html
// See also PaintLayerPainter (in particular paintLayerContents) for
// our implementation of the walk.
//
// Stacked elements form a subtree over the layout tree. Ideally we would want
// objects of this class to be a node in this tree but there are potential
// issues with stale pointers so we rely on PaintLayer's tree structure.
//
// This class's purpose is to represent a node in the stacked element tree
// (aka paint tree). It currently caches the z-order lists for painting and
// hit-testing.
//
// To implement any paint order iterations, use PaintLayerPaintOrderIterator and
// PaintLayerZOrderReverseIterator.
//
// We create PaintLayerStackingNode only for real stacking contexts with stacked
// children. PaintLayerPaintOrder[Reverse]Iterator can iterate normal flow
// children in paint order with or without a stacking node.
class CORE_EXPORT PaintLayerStackingNode
    : public GarbageCollected<PaintLayerStackingNode> { … };

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_PAINT_LAYER_STACKING_NODE_H_