1 files changed, 28 insertions, 13 deletions

diff --git a/chromium/third_party/blink/renderer/platform/graphics/paint/geometry_mapper.h b/chromium/third_party/blink/renderer/platform/graphics/paint/geometry_mapper.h
index 1b3a89b2fba..9c6a9173b98 100644
--- a/chromium/third_party/blink/renderer/platform/graphics/paint/geometry_mapper.h
+++ b/chromium/third_party/blink/renderer/platform/graphics/paint/geometry_mapper.h
@@ -18,15 +18,27 @@ namespace blink {
 // Clips can use FloatRect::Intersect or FloatRect::InclusiveIntersect.
 enum InclusiveIntersectOrNot { kNonInclusiveIntersect, kInclusiveIntersect };
 
-// Whether to expand the visual or clip rect to infinity when we meet any
-// animating transform or filter when walking from a descendant state to an
+// When performing overlap testing during compositing, we may need to expand the
+// visual rect in two cases when mapping from descendant state to ancestor
+// state: mapping through a fixed transform node to the viewport it is attached
+// to, and mapping through an animating transform or filter.
+//
+// This allows for a more conservative overlap test that assumes potentially
+// more overlap than we'd encounter otherwise, in order to reduce the need to
+// re-run overlap testing in response to things like scrolling.
+//
+// The expansion for fixed covers all coordinates where the fixed content may
+// end up when the scroller is at the end of the extents.
+//
+// For animation, the visual or clip rect is expanded to infinity when we meet
+// any animating transform or filter when walking from a descendant state to an
 // ancestor state, when mapping a visual rect or getting the accumulated clip
 // rect. After we expanded the rect, we will still apply ancestor clips when
 // continuing walking up the tree. TODO(crbug.com/1026653): Consider animation
 // bounds instead of using infinite rect.
-enum ExpandVisualRectForAnimationOrNot {
-  kDontExpandVisualRectForAnimation,
-  kExpandVisualRectForAnimation,
+enum ExpandVisualRectForCompositingOverlapOrNot {
+  kDontExpandVisualRectForCompositingOverlap,
+  kExpandVisualRectForCompositingOverlap,
 };
 
 // GeometryMapper is a helper class for fast computations of transformed and
@@ -186,9 +198,10 @@ class PLATFORM_EXPORT GeometryMapper {
     }
 
     bool has_animation = false;
+    bool has_fixed = false;
     bool success = false;
     const auto& source_to_destination = SourceToDestinationProjectionInternal(
-        source, destination, has_animation, success);
+        source, destination, has_animation, has_fixed, success);
     if (!success)
       mapping_rect = Rect();
     else
@@ -263,11 +276,11 @@ class PLATFORM_EXPORT GeometryMapper {
       FloatClipRect& mapping_rect,
       OverlayScrollbarClipBehavior clip = kIgnoreOverlayScrollbarSize,
       InclusiveIntersectOrNot intersect = kNonInclusiveIntersect,
-      ExpandVisualRectForAnimationOrNot animation =
-          kDontExpandVisualRectForAnimation) {
+      ExpandVisualRectForCompositingOverlapOrNot expand =
+          kDontExpandVisualRectForCompositingOverlap) {
     return LocalToAncestorVisualRect(local_state.Unalias(),
                                      ancestor_state.Unalias(), mapping_rect,
-                                     clip, intersect, animation);
+                                     clip, intersect, expand);
   }
   static bool LocalToAncestorVisualRect(
       const PropertyTreeState& local_state,
@@ -275,7 +288,8 @@ class PLATFORM_EXPORT GeometryMapper {
       FloatClipRect& mapping_rect,
       OverlayScrollbarClipBehavior = kIgnoreOverlayScrollbarSize,
       InclusiveIntersectOrNot = kNonInclusiveIntersect,
-      ExpandVisualRectForAnimationOrNot = kDontExpandVisualRectForAnimation);
+      ExpandVisualRectForCompositingOverlapOrNot =
+          kDontExpandVisualRectForCompositingOverlap);
 
   static void ClearCache();
 
@@ -289,6 +303,7 @@ class PLATFORM_EXPORT GeometryMapper {
       const TransformPaintPropertyNode& source,
       const TransformPaintPropertyNode& destination,
       bool& has_animation,
+      bool& has_fixed,
       bool& success);
 
   static FloatClipRect LocalToAncestorClipRectInternal(
@@ -297,7 +312,7 @@ class PLATFORM_EXPORT GeometryMapper {
       const TransformPaintPropertyNode& ancestor_transform,
       OverlayScrollbarClipBehavior,
       InclusiveIntersectOrNot,
-      ExpandVisualRectForAnimationOrNot,
+      ExpandVisualRectForCompositingOverlapOrNot,
       bool& success);
 
   // The return value has the same meaning as that for
@@ -308,7 +323,7 @@ class PLATFORM_EXPORT GeometryMapper {
       FloatClipRect& mapping_rect,
       OverlayScrollbarClipBehavior,
       InclusiveIntersectOrNot,
-      ExpandVisualRectForAnimationOrNot,
+      ExpandVisualRectForCompositingOverlapOrNot,
       bool& success);
 
   // The return value has the same meaning as that for
@@ -319,7 +334,7 @@ class PLATFORM_EXPORT GeometryMapper {
       FloatClipRect& mapping_rect,
       OverlayScrollbarClipBehavior,
       InclusiveIntersectOrNot,
-      ExpandVisualRectForAnimationOrNot,
+      ExpandVisualRectForCompositingOverlapOrNot,
       bool& success);
 
   static void MoveRect(FloatRect& rect, const FloatSize& delta) {