Bug 1178765 - Part 4: Force a display list rebuild when backdrop-filter pref is toggled r=mstange

Differential Revision: https://phabricator.services.mozilla.com/D40665

--HG--
extra : moz-landing-system : lando

layout/base/nsLayoutUtils.cpp

@@ -3963,16 +3963,11 @@ nsresult nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext,
       DisplayListChecker toBeMergedChecker;
       DisplayListChecker afterMergeChecker;
 
-      // If we transition between wrapping the RCD-RSF contents into an async
-      // zoom container vs. not, we need to rebuild the display list. This only
-      // happens when the zooming or container scrolling prefs are toggled
-      // (manually by the user, or during test setup).
+      // If a pref is toggled that adds or removes display list items,
+      // we need to rebuild the display list. The pref may be toggled
+      // manually by the user, or during test setup.
       bool shouldAttemptPartialUpdate = useRetainedBuilder;
-      bool didBuildAsyncZoomContainer =
-          builder->ShouldBuildAsyncZoomContainer();
-      builder->UpdateShouldBuildAsyncZoomContainer();
-      if (builder->ShouldBuildAsyncZoomContainer() !=
-          didBuildAsyncZoomContainer) {
+      if (builder->ShouldRebuildDisplayListDueToPrefChange()) {
         shouldAttemptPartialUpdate = false;
       }
 

layout/painting/nsDisplayList.cpp

@@ -1273,13 +1273,14 @@ nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
       mPartialBuildFailed(false),
       mIsInActiveDocShell(false),
       mBuildAsyncZoomContainer(false),
+      mBuildBackdropRootContainer(false),
       mHitTestArea(),
       mHitTestInfo(CompositorHitTestInvisibleToHit) {
   MOZ_COUNT_CTOR(nsDisplayListBuilder);
 
   mBuildCompositorHitTestInfo = mAsyncPanZoomEnabled && IsForPainting();
 
-  UpdateShouldBuildAsyncZoomContainer();
+  ShouldRebuildDisplayListDueToPrefChange();
 
   static_assert(
       static_cast<uint32_t>(DisplayItemType::TYPE_MAX) < (1 << TYPE_BITS),
@@ -1509,6 +1510,38 @@ void nsDisplayListBuilder::UpdateShouldBuildAsyncZoomContainer() {
       !StaticPrefs::layout_scroll_root_frame_containers();
 }
 
+void nsDisplayListBuilder::UpdateShouldBuildBackdropRootContainer() {
+  mBuildBackdropRootContainer =
+      StaticPrefs::layout_css_backdrop_filter_enabled();
+}
+
+// Certain prefs may cause display list items to be added or removed when they
+// are toggled. In those cases, we need to fully rebuild the display list.
+bool nsDisplayListBuilder::ShouldRebuildDisplayListDueToPrefChange() {
+  bool shouldRebuild = false;
+
+  // If we transition between wrapping the RCD-RSF contents into an async
+  // zoom container vs. not, we need to rebuild the display list. This only
+  // happens when the zooming or container scrolling prefs are toggled
+  // (manually by the user, or during test setup).
+  bool didBuildAsyncZoomContainer = mBuildAsyncZoomContainer;
+  UpdateShouldBuildAsyncZoomContainer();
+  if (didBuildAsyncZoomContainer != mBuildAsyncZoomContainer) {
+    shouldRebuild = true;
+  }
+
+  // If backdrop-filter is enabled, backdrop root containers are added to the
+  // display list. When the pref is toggled these containers may be added or
+  // removed, so the display list should be rebuilt.
+  bool didBuildBackdropRootContainer = mBuildBackdropRootContainer;
+  UpdateShouldBuildBackdropRootContainer();
+  if (didBuildBackdropRootContainer != mBuildBackdropRootContainer) {
+    shouldRebuild = true;
+  }
+
+  return shouldRebuild;
+}
+
 bool nsDisplayListBuilder::MarkOutOfFlowFrameForDisplay(nsIFrame* aDirtyFrame,
                                                         nsIFrame* aFrame) {
   MOZ_ASSERT(aFrame->GetParent() == aDirtyFrame);

layout/painting/nsDisplayList.h

@@ -1743,6 +1743,10 @@ class nsDisplayListBuilder {
   }
   void UpdateShouldBuildAsyncZoomContainer();
 
+  void UpdateShouldBuildBackdropRootContainer();
+
+  bool ShouldRebuildDisplayListDueToPrefChange();
+
   /**
    * Represents a region composed of frame/rect pairs.
    * WeakFrames are used to track whether a rect still belongs to the region.
@@ -2020,6 +2024,7 @@ class nsDisplayListBuilder {
   bool mPartialBuildFailed;
   bool mIsInActiveDocShell;
   bool mBuildAsyncZoomContainer;
+  bool mBuildBackdropRootContainer;
 
   nsRect mHitTestArea;
   CompositorHitTestInfo mHitTestInfo;