tor-browser

commit 8a183125a82f2c1c1eb4cf2dce05c52f124d2719
parent 807658efa8c0c99e018d2b8c0fc456be20448dd6
Author: Botond Ballo <botond@mozilla.com>
Date:   Thu, 13 Nov 2025 04:59:03 +0000

Bug 1730749 - Store the 'should flatten' flag on StickyScrollContainer. r=mstange

This allows the code that checks the flag to avoid needing the
sticky display item.

Differential Revision: https://phabricator.services.mozilla.com/D254146

Diffstat:
M
layout/generic/StickyScrollContainer.h
 | 
6
++++++
M
layout/generic/nsIFrame.cpp
 | 
15
++++++++++++---

2 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/layout/generic/StickyScrollContainer.h b/layout/generic/StickyScrollContainer.h
@@ -85,6 +85,11 @@ class StickyScrollContainer final {
    */
   void MarkFramesForReflow();
 
+  void SetShouldFlatten(bool aShouldFlatten) {
+    mShouldFlatten = aShouldFlatten;
+  }
+  bool ShouldFlattenAway() const { return mShouldFlatten; }
+
   explicit StickyScrollContainer(ScrollContainerFrame* aScrollContainerFrame);
 
  private:
@@ -100,6 +105,7 @@ class StickyScrollContainer final {
   ScrollContainerFrame* const mScrollContainerFrame;
   DepthOrderedFrameList mFrames;
   nsPoint mScrollPosition;
+  bool mShouldFlatten = false;
 };
 
 }  // namespace mozilla
diff --git a/layout/generic/nsIFrame.cpp b/layout/generic/nsIFrame.cpp
@@ -3904,9 +3904,18 @@ void nsIFrame::BuildDisplayListForStackingContext(
         aBuilder->CurrentActiveScrolledRoot(),
         clipState.IsClippedToDisplayPort());
 
-    auto* ssc = StickyScrollContainer::GetOrCreateForFrame(this);
-    const bool shouldFlatten =
-        !ssc || !ssc->ScrollContainer()->IsMaybeAsynchronouslyScrolled();
+    bool shouldFlatten = true;
+
+    StickyScrollContainer* stickyScrollContainer =
+        StickyScrollContainer::GetOrCreateForFrame(this);
+    if (stickyScrollContainer) {
+      if (stickyScrollContainer->ScrollContainer()
+              ->IsMaybeAsynchronouslyScrolled()) {
+        shouldFlatten = false;
+      }
+      stickyScrollContainer->SetShouldFlatten(shouldFlatten);
+    }
+
     stickyItem->SetShouldFlatten(shouldFlatten);
 
     resultList.AppendToTop(stickyItem);