[tbb-commits] [tor-browser] 265/311: Bug 1736069 - Unconditionally create nsDisplayStickyPosition items r=tnikkel a=dmeehan

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pierov pushed a commit to branch geckoview-99.0.1-11.0-1
in repository tor-browser.

commit d8d3ed7215b641eb2d5af77082c3398946606a5a
Author: Miko Mynttinen <mikokm at gmail.com>
AuthorDate: Thu Mar 24 17:40:32 2022 +0000

    Bug 1736069 - Unconditionally create nsDisplayStickyPosition items r=tnikkel a=dmeehan
    
    Differential Revision: https://phabricator.services.mozilla.com/D141925
---
 layout/generic/nsIFrame.cpp                    | 28 ++++++++++++++++----------
 layout/painting/RetainedDisplayListBuilder.cpp |  4 +++-
 layout/painting/nsDisplayList.h                | 14 ++++++++++++-
 3 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/layout/generic/nsIFrame.cpp b/layout/generic/nsIFrame.cpp
index be46eba2110bc..c2c4d31eb218c 100644
--- a/layout/generic/nsIFrame.cpp
+++ b/layout/generic/nsIFrame.cpp
@@ -3349,15 +3349,7 @@ void nsIFrame::BuildDisplayListForStackingContext(
     aBuilder->EnterSVGEffectsContents(this, &hoistedScrollInfoItemsStorage);
   }
 
-  bool useStickyPosition = false;
-  if (disp->mPosition == StylePositionProperty::Sticky) {
-    StickyScrollContainer* stickyScrollContainer =
-        StickyScrollContainer::GetStickyScrollContainerForFrame(this);
-    if (stickyScrollContainer &&
-        stickyScrollContainer->ScrollFrame()->IsMaybeAsynchronouslyScrolled()) {
-      useStickyPosition = true;
-    }
-  }
+  bool useStickyPosition = disp->mPosition == StylePositionProperty::Sticky;
 
   bool useFixedPosition =
       disp->mPosition == StylePositionProperty::Fixed &&
@@ -3837,11 +3829,25 @@ void nsIFrame::BuildDisplayListForStackingContext(
     // descendants).
     const ActiveScrolledRoot* stickyASR = ActiveScrolledRoot::PickAncestor(
         containerItemASR, aBuilder->CurrentActiveScrolledRoot());
-    resultList.AppendNewToTop<nsDisplayStickyPosition>(
+
+    auto* stickyItem = MakeDisplayItem<nsDisplayStickyPosition>(
         aBuilder, this, &resultList, stickyASR,
         aBuilder->CurrentActiveScrolledRoot(),
         clipState.IsClippedToDisplayPort());
-    ct.TrackContainer(resultList.GetTop());
+
+    bool shouldFlatten = true;
+
+    StickyScrollContainer* stickyScrollContainer =
+        StickyScrollContainer::GetStickyScrollContainerForFrame(this);
+    if (stickyScrollContainer &&
+        stickyScrollContainer->ScrollFrame()->IsMaybeAsynchronouslyScrolled()) {
+      shouldFlatten = false;
+    }
+
+    stickyItem->SetShouldFlatten(shouldFlatten);
+
+    resultList.AppendToTop(stickyItem);
+    ct.TrackContainer(stickyItem);
 
     // If the sticky element is inside a filter, annotate the scroll frame that
     // scrolls the filter as having out-of-flow content inside a filter (this
diff --git a/layout/painting/RetainedDisplayListBuilder.cpp b/layout/painting/RetainedDisplayListBuilder.cpp
index 2af75e88f207c..1bd2b49b25a6b 100644
--- a/layout/painting/RetainedDisplayListBuilder.cpp
+++ b/layout/painting/RetainedDisplayListBuilder.cpp
@@ -596,10 +596,12 @@ class MergeState {
       return true;
     }
 
-    if (type == DisplayItemType::TYPE_SUBDOCUMENT) {
+    if (type == DisplayItemType::TYPE_SUBDOCUMENT ||
+        type == DisplayItemType::TYPE_STICKY_POSITION) {
       // nsDisplaySubDocument::mShouldFlatten can change without an invalidation
       // (and is the reason we unconditionally build the subdocument item), so
       // always use the new one to make sure we get the right value.
+      // Same for |nsDisplayStickyPosition::mShouldFlatten|.
       return true;
     }
 
diff --git a/layout/painting/nsDisplayList.h b/layout/painting/nsDisplayList.h
index b41bb874c1f04..fab406241272f 100644
--- a/layout/painting/nsDisplayList.h
+++ b/layout/painting/nsDisplayList.h
@@ -5532,7 +5532,8 @@ class nsDisplayStickyPosition : public nsDisplayOwnLayer {
                           const nsDisplayStickyPosition& aOther)
       : nsDisplayOwnLayer(aBuilder, aOther),
         mContainerASR(aOther.mContainerASR),
-        mClippedToDisplayPort(aOther.mClippedToDisplayPort) {
+        mClippedToDisplayPort(aOther.mClippedToDisplayPort),
+        mShouldFlatten(false) {
     MOZ_COUNT_CTOR(nsDisplayStickyPosition);
   }
 
@@ -5564,6 +5565,14 @@ class nsDisplayStickyPosition : public nsDisplayOwnLayer {
 
   bool CanMoveAsync() override { return true; }
 
+  void SetShouldFlatten(bool aShouldFlatten) {
+    mShouldFlatten = aShouldFlatten;
+  }
+
+  bool ShouldFlattenAway(nsDisplayListBuilder* aBuilder) final {
+    return mShouldFlatten;
+  }
+
  private:
   NS_DISPLAY_ALLOW_CLONING()
 
@@ -5590,6 +5599,9 @@ class nsDisplayStickyPosition : public nsDisplayOwnLayer {
   // checkerboarded. Note that the sticky item will still be subject to the
   // scrollport clip.
   bool mClippedToDisplayPort;
+
+  // True if this item should be flattened away.
+  bool mShouldFlatten;
 };
 
 class nsDisplayFixedPosition : public nsDisplayOwnLayer {

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