gecko-dev/layout/painting/DisplayItemClipChain.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef DISPLAYITEMCLIPCHAIN_H_
#define DISPLAYITEMCLIPCHAIN_H_

#include "mozilla/Assertions.h"
#include "DisplayItemClip.h"
#include "nsString.h"

class nsIScrollableFrame;

namespace mozilla {

struct ActiveScrolledRoot;

/**
 * A DisplayItemClipChain is a linked list of DisplayItemClips where each clip
 * is associated with an active scrolled root that describes what the clip
 * moves with.
 * We use a chain instead of just one intersected clip due to async scrolling:
 * A clip that moves along with a display item can be fused to the item's
 * contents when drawing the layer contents, but all other clips in the chain
 * need to be kept separate so that they can be applied at composition time,
 * after any async scroll offsets have been applied.
 * The clip chain is created during display list construction by the builder's
 * DisplayListClipState.
 * The clip chain order is determined by the active scrolled root order.
 * For every DisplayItemClipChain object |clipChain|, the following holds:
 * !clipChain->mParent ||
 * ActiveScrolledRoot::IsAncestor(clipChain->mParent->mASR, clipChain->mASR).
 * The clip chain can skip over active scrolled roots. That just means that
 * there is no clip that moves with the skipped ASR in this chain.
 */
struct DisplayItemClipChain
{

  /**
   * Get the display item clip in this chain that moves with aASR, or nullptr
   * if no such clip exists. aClipChain can be null.
   */
  static const DisplayItemClip* ClipForASR(
    const DisplayItemClipChain* aClipChain,
    const ActiveScrolledRoot* aASR);

  static bool Equal(const DisplayItemClipChain* aClip1,
                    const DisplayItemClipChain* aClip2);
  /**
   * Hash function that returns the same value for any two clips A and B
   * where Equal(A, B) is true.
   */
  static uint32_t Hash(const DisplayItemClipChain* aClip);

  static nsCString ToString(const DisplayItemClipChain* aClipChain);

  bool HasRoundedCorners() const;

  void AddRef() { mRefCount++; }
  void Release()
  {
    MOZ_ASSERT(mRefCount > 0);
    mRefCount--;
  }

  DisplayItemClipChain(const DisplayItemClip& aClip,
                       const ActiveScrolledRoot* aASR,
                       const DisplayItemClipChain* aParent,
                       DisplayItemClipChain* aNextClipChainToDestroy)
    : mClip(aClip)
    , mASR(aASR)
    , mParent(aParent)
    , mNextClipChainToDestroy(aNextClipChainToDestroy)
#ifdef DEBUG
    , mOnStack(true)
#endif
  {
  }

  DisplayItemClipChain()
    : mASR(nullptr)
    , mNextClipChainToDestroy(nullptr)
#ifdef DEBUG
    , mOnStack(true)
#endif
  {
  }

  DisplayItemClip mClip;
  const ActiveScrolledRoot* mASR;
  RefPtr<const DisplayItemClipChain> mParent;
  uint32_t mRefCount = 0;
  DisplayItemClipChain* mNextClipChainToDestroy;
#ifdef DEBUG
  bool mOnStack;
#endif
};

struct DisplayItemClipChainHasher
{
  typedef const DisplayItemClipChain* Key;

  std::size_t operator()(const Key& aKey) const
  {
    return DisplayItemClipChain::Hash(aKey);
  }
};

struct DisplayItemClipChainEqualer
{
  typedef const DisplayItemClipChain* Key;

  bool operator()(const Key& lhs, const Key& rhs) const
  {
    return DisplayItemClipChain::Equal(lhs, rhs);
  }
};

} // namespace mozilla

#endif /* DISPLAYITEMCLIPCHAIN_H_ */