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/* -*- 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 */
#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);
DisplayItemClipChain(const DisplayItemClip& aClip,
const ActiveScrolledRoot* aASR,
const DisplayItemClipChain* aParent,
DisplayItemClipChain* aNextClipChainToDestroy)
: mClip(aClip),
: mASR(nullptr),
DisplayItemClip mClip;
const ActiveScrolledRoot* mASR;
RefPtr<const DisplayItemClipChain> mParent;
uint32_t mRefCount = 0;
DisplayItemClipChain* mNextClipChainToDestroy;
bool mOnStack;
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