tor-browser

commit 629ba9fbd736e50ece755fcda4212db11650f80c
parent e4cfc7d3e0b15330d8ee87620d8bb3597e7d8ac5
Author: Timothy Nikkel <tnikkel@gmail.com>
Date:   Sun, 23 Nov 2025 05:52:39 +0200

Bug 2001802. Ensure that DisablePartialUpdates gets cleared if we do a full rebuild. r?#layout-reviewers,#gfx-reviewers DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D273718

Diffstat:
M
layout/base/nsLayoutUtils.cpp
 | 
6
++++++
M
layout/painting/RetainedDisplayListBuilder.cpp
 | 
18
+++++++++---------

2 files changed, 15 insertions(+), 9 deletions(-)
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
@@ -3084,6 +3084,12 @@ void nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext, nsIFrame* aFrame,
       DL_LOGI("Partial updates are disabled");
       metrics->mPartialUpdateResult = PartialUpdateResult::Failed;
       metrics->mPartialUpdateFailReason = PartialUpdateFailReason::Disabled;
+
+      // Now that we've decided to do a full rebuild make sure to clear the
+      // disable partial updates bool so that we can maybe attempt a partial
+      // update on the paint after this one (if it doesn't get disabled again
+      // during this paint).
+      builder->SetDisablePartialUpdates(false);
     }
 
     // Rebuild the full display list if the partial display list build failed.
diff --git a/layout/painting/RetainedDisplayListBuilder.cpp b/layout/painting/RetainedDisplayListBuilder.cpp
@@ -1265,6 +1265,15 @@ bool RetainedDisplayListBuilder::ComputeRebuildRegion(
 
 bool RetainedDisplayListBuilder::ShouldBuildPartial(
     nsTArray<nsIFrame*>& aModifiedFrames) {
+  // We don't support retaining with overlay scrollbars, since they require
+  // us to look at the display list and pick the highest z-index, which
+  // we can't do during partial building.
+  if (mBuilder.DisablePartialUpdates()) {
+    mBuilder.SetDisablePartialUpdates(false);
+    Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::Disabled;
+    return false;
+  }
+
   if (mList.IsEmpty()) {
     // Partial builds without a previous display list do not make sense.
     Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::EmptyList;
@@ -1278,15 +1287,6 @@ bool RetainedDisplayListBuilder::ShouldBuildPartial(
     return false;
   }
 
-  // We don't support retaining with overlay scrollbars, since they require
-  // us to look at the display list and pick the highest z-index, which
-  // we can't do during partial building.
-  if (mBuilder.DisablePartialUpdates()) {
-    mBuilder.SetDisablePartialUpdates(false);
-    Metrics()->mPartialUpdateFailReason = PartialUpdateFailReason::Disabled;
-    return false;
-  }
-
   for (nsIFrame* f : aModifiedFrames) {
     MOZ_ASSERT(f);