chromium/third_party/blink/renderer/core/layout/anchor_position_scroll_data.h

// 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_ANCHOR_POSITION_SCROLL_DATA_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_ANCHOR_POSITION_SCROLL_DATA_H_

#include "third_party/blink/renderer/core/dom/element_rare_data_field.h"
#include "third_party/blink/renderer/core/layout/geometry/physical_offset.h"
#include "third_party/blink/renderer/core/scroll/scroll_snapshot_client.h"
#include "third_party/blink/renderer/platform/graphics/compositor_element_id.h"
#include "third_party/blink/renderer/platform/heap/member.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"
#include "ui/gfx/geometry/vector2d.h"
#include "ui/gfx/geometry/vector2d_f.h"

namespace blink {

class AnchorPositionVisibilityObserver;
class Element;
class LayoutObject;

// Created for each anchor-positioned element.
//
// https://drafts.csswg.org/css-anchor-position-1/#scroll
//
// To adjust the location of the anchor-positioned element based on scroll,
// sticky and anchor-positioning offsets between this element and the anchor,
// this class stores a snapshot of all the scroll adjustment containers [1] of
// the anchor up to the containing block (exclusively) of the anchor-positioned
// element, along the containing block hierarchy. Note that "containing block"
// is in the spec meaning, which corresponds to LayoutObject::Container()
// instead of ContainingBlock().
//
// [1] An element is a scroll adjustment container if it is a scroll container,
// has sticky position, or is anchor-positioned.
//
// https://drafts.csswg.org/css-anchor-position-1/#fallback
//
// Also stores a snapshot of the scroll offset of the scroll container of the
// anchor-positioned element, which affects position fallback.
//
// The snapshot passed as input to the position fallback and position visibility
// algorithm.
//
// The snapshot is updated once per frame update on top of animation frame to
// avoid layout cycling. If there is any change, we trigger an update to
// layout and/or paint.
class AnchorPositionScrollData
    : public GarbageCollected<AnchorPositionScrollData>,
      public ScrollSnapshotClient,
      public ElementRareDataField { … };

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

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_ANCHOR_POSITION_SCROLL_DATA_H_