From 51b371636c46b8f0156e81e048c51f81fc92f790 Mon Sep 17 00:00:00 2001
From: Matt Woodrow <mwoodrow@mozilla.com>
Date: Mon, 6 Sep 2021 23:12:04 +0000
Subject: [PATCH] Bug 1728251 - Remove mClip and compute it when we need it.
 r=miko

Differential Revision: https://phabricator.services.mozilla.com/D124008
---
 layout/painting/nsDisplayList.cpp | 24 +++++++-----------------
 layout/painting/nsDisplayList.h   | 13 +++++--------
 2 files changed, 12 insertions(+), 25 deletions(-)

diff --git a/layout/painting/nsDisplayList.cpp b/layout/painting/nsDisplayList.cpp
index 6cd1ccb84719..3324dfb77254 100644
--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -2771,8 +2771,7 @@ nsDisplayItem::nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
       aBuilder->GetVisibleRect().width >= 0 || !aBuilder->IsForPainting(),
       "visible rect not set");
 
-  nsDisplayItem::SetClipChain(
-      aBuilder->ClipState().GetCurrentCombinedClipChain(aBuilder), true);
+  mClipChain = aBuilder->ClipState().GetCurrentCombinedClipChain(aBuilder);
 
   // The visible rect is for mCurrentFrame, so we have to use
   // mCurrentOffsetToReferenceFrame
@@ -2809,7 +2808,6 @@ int32_t nsDisplayItem::ZIndex() const { return mFrame->ZIndex().valueOr(0); }
 void nsDisplayItem::SetClipChain(const DisplayItemClipChain* aClipChain,
                                  bool aStore) {
   mClipChain = aClipChain;
-  mClip = DisplayItemClipChain::ClipForASR(aClipChain, mActiveScrolledRoot);
 }
 
 Maybe<nsRect> nsDisplayItem::GetClipWithRespectToASR(
@@ -2824,6 +2822,12 @@ Maybe<nsRect> nsDisplayItem::GetClipWithRespectToASR(
   return Nothing();
 }
 
+const DisplayItemClip& nsDisplayItem::GetClip() const {
+  const DisplayItemClip* clip =
+      DisplayItemClipChain::ClipForASR(mClipChain, mActiveScrolledRoot);
+  return clip ? *clip : DisplayItemClip::NoClip();
+}
+
 void nsDisplayItem::IntersectClip(nsDisplayListBuilder* aBuilder,
                                   const DisplayItemClipChain* aOther,
                                   bool aStore) {
@@ -5819,20 +5823,6 @@ nsDisplayStickyPosition::nsDisplayStickyPosition(
   MOZ_COUNT_CTOR(nsDisplayStickyPosition);
 }
 
-void nsDisplayStickyPosition::SetClipChain(
-    const DisplayItemClipChain* aClipChain, bool aStore) {
-  mClipChain = aClipChain;
-  mClip = nullptr;
-
-  MOZ_ASSERT(!mClip,
-             "There should never be a clip on this item because no clip moves "
-             "with it.");
-
-  if (aStore) {
-    mOriginalClipChain = aClipChain;
-  }
-}
-
 // Returns the smallest distance from "0" to the range [min, max] where
 // min <= max. Despite the name, the return value is actually a 1-D vector,
 // and so may be negative if max < 0.
diff --git a/layout/painting/nsDisplayList.h b/layout/painting/nsDisplayList.h
index 23d98839cfc4..4a8051e77dfb 100644
--- a/layout/painting/nsDisplayList.h
+++ b/layout/painting/nsDisplayList.h
@@ -2387,8 +2387,7 @@ class nsDisplayItem : public nsDisplayItemLink {
         mToReferenceFrame(aOther.mToReferenceFrame),
         mAnimatedGeometryRoot(aOther.mAnimatedGeometryRoot),
         mActiveScrolledRoot(aOther.mActiveScrolledRoot),
-        mClipChain(aOther.mClipChain),
-        mClip(aOther.mClip) {
+        mClipChain(aOther.mClipChain) {
     MOZ_COUNT_CTOR(nsDisplayItem);
     // TODO: It might be better to remove the flags that aren't copied.
     if (aOther.ForceNotVisible()) {
@@ -2841,9 +2840,7 @@ class nsDisplayItem : public nsDisplayItemLink {
 
   virtual bool SupportsOptimizingToImage() const { return false; }
 
-  const DisplayItemClip& GetClip() const {
-    return mClip ? *mClip : DisplayItemClip::NoClip();
-  }
+  virtual const DisplayItemClip& GetClip() const;
   void IntersectClip(nsDisplayListBuilder* aBuilder,
                      const DisplayItemClipChain* aOther, bool aStore);
 
@@ -2962,7 +2959,6 @@ class nsDisplayItem : public nsDisplayItemLink {
   RefPtr<AnimatedGeometryRoot> mAnimatedGeometryRoot;
   RefPtr<const ActiveScrolledRoot> mActiveScrolledRoot;
   RefPtr<const DisplayItemClipChain> mClipChain;
-  const DisplayItemClip* mClip = nullptr;
 
 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
  public:
@@ -5609,8 +5605,9 @@ class nsDisplayStickyPosition : public nsDisplayOwnLayer {
 
   MOZ_COUNTED_DTOR_OVERRIDE(nsDisplayStickyPosition)
 
-  void SetClipChain(const DisplayItemClipChain* aClipChain,
-                    bool aStore) override;
+  const DisplayItemClip& GetClip() const override {
+    return DisplayItemClip::NoClip();
+  }
   bool IsClippedToDisplayPort() const { return mClippedToDisplayPort; }
 
   NS_DISPLAY_DECL_NAME("StickyPosition", TYPE_STICKY_POSITION)