[NOT FOR REVIEW]

cc/trees/property_tree_builder.cc

Index: cc/trees/property_tree_builder.cc
diff --git a/cc/trees/property_tree_builder.cc b/cc/trees/property_tree_builder.cc
index d99262f84e268156ac925bafd5a8b9ef5092d462..c2f67ad3b087a68a42b8f8d361910a16f5452d71 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -456,6 +456,81 @@ void AddClipNodeIfNeeded(const DataForRecursion<LayerType>& data_from_ancestor,
 }
 
 template <typename LayerType>
+void AddClipNodeOnlyIfLayerClipsSubtree(
+    const DataForRecursion<LayerType>& data_from_ancestor,
+    LayerType* layer,
+    bool created_render_surface,
+    bool created_transform_node,
+    DataForRecursion<LayerType>* data_for_children) {
+  const bool inherits_clip = !ClipParent(layer);
+  const int parent_id = inherits_clip ? data_from_ancestor.clip_tree_parent
+                                      : ClipParent(layer)->clip_tree_index();
+  ClipNode* parent =
+      data_from_ancestor.property_trees->clip_tree.Node(parent_id);
+
+  bool apply_ancestor_clip = false;
+  if (inherits_clip) {
+    apply_ancestor_clip = data_from_ancestor.apply_ancestor_clip;
+  } else {
+    const EffectNode* parent_effect_node =
+        data_from_ancestor.property_trees->effect_tree.Node(
+            ClipParent(layer)->effect_tree_index());
+    if (parent_effect_node->clip_id == parent->id) {
+      if (parent_effect_node->surface_is_clipped) {
+        // In this case, there is no clipping layer between the clip parent and
+        // its target and the target has applied the clip.
+        apply_ancestor_clip = false;
+      } else {
+        // In this case, there is no clipping layer between the clip parent and
+        // its target and the target has not applied the clip. There are two
+        // cases when a target doesn't apply clip. First, there is no ancestor
+        // clip to apply, in this case apply_ancestor_clip should be false.
+        // Second, there is a clip to apply but there are unclipped descendants,
+        // so the target cannot apply the clip. In this case,
+        // apply_ancestor_clip should be true.
+        apply_ancestor_clip = parent_effect_node->has_unclipped_descendants;
+      }
+    } else {
+      // In this case, there is a clipping layer between the clip parent and
+      // its target.
+      apply_ancestor_clip = true;
+    }
+  }
+  if (created_render_surface)
+    SetSurfaceIsClipped(data_for_children, apply_ancestor_clip, layer);
+
+  bool layer_clips_subtree = LayerClipsSubtree(layer);
+  if (layer_clips_subtree) {
+    data_for_children->apply_ancestor_clip = true;
+  }
+
+  if (!layer_clips_subtree) {
+    data_for_children->clip_tree_parent = parent_id;
+  } else {
+    LayerType* transform_parent = data_for_children->transform_tree_parent;
+    if (PositionConstraint(layer).is_fixed_position() &&
+        !created_transform_node) {
+      transform_parent = data_for_children->transform_fixed_parent;
+    }
+    ClipNode node;
+    node.clip = gfx::RectF(gfx::PointF() + layer->offset_to_transform_parent(),
+                           gfx::SizeF(layer->bounds()));
+    node.transform_id = transform_parent->transform_tree_index();
+    node.owner_id = layer->id();
+    if (layer_clips_subtree)
+      node.clip_type = ClipNode::ClipType::APPLIES_LOCAL_CLIP;
+    else
+      node.clip_type = ClipNode::ClipType::NONE;
+    data_for_children->clip_tree_parent =
+        data_for_children->property_trees->clip_tree.Insert(node, parent_id);
+    data_for_children->property_trees->clip_id_to_index_map[layer->id()] =
+        data_for_children->clip_tree_parent;
+  }
+
+  layer->SetNewClipTreeIndex(data_for_children->clip_tree_parent);
+}
+
+template <typename LayerType>
 static inline bool IsAtBoundaryOf3dRenderingContext(LayerType* layer) {
   return Parent(layer)
              ? Parent(layer)->sorting_context_id() !=
@@ -1239,7 +1314,8 @@ template <typename LayerType>
 void BuildPropertyTreesInternal(
     LayerType* layer,
     const DataForRecursion<LayerType>& data_from_parent,
-    DataForRecursionFromChild<LayerType>* data_to_parent) {
+    DataForRecursionFromChild<LayerType>* data_to_parent,
+    bool build_new_clip_tree) {
   layer->set_property_tree_sequence_number(
       data_from_parent.property_trees->sequence_number);
 
@@ -1257,8 +1333,12 @@ void BuildPropertyTreesInternal(
 
   bool created_transform_node = AddTransformNodeIfNeeded(
       data_from_parent, layer, created_render_surface, &data_for_children);
-  AddClipNodeIfNeeded(data_from_parent, layer, created_render_surface,
-                      created_transform_node, &data_for_children);
+  if (build_new_clip_tree)
+    AddClipNodeOnlyIfLayerClipsSubtree(data_from_parent, layer, created_render_surface,
+                        created_transform_node, &data_for_children);
+  else
+    AddClipNodeIfNeeded(data_from_parent, layer, created_render_surface,
+                        created_transform_node, &data_for_children);
 
   AddScrollNodeIfNeeded(data_from_parent, layer, &data_for_children);
 
@@ -1271,7 +1351,7 @@ void BuildPropertyTreesInternal(
     if (!ScrollParent(current_child)) {
       DataForRecursionFromChild<LayerType> data_from_child;
       BuildPropertyTreesInternal(current_child, data_for_children,
-                                 &data_from_child);
+                                 &data_from_child, build_new_clip_tree);
       data_to_parent->Merge(data_from_child);
     } else {
       // The child should be included in its scroll parent's list of scroll
@@ -1290,7 +1370,7 @@ void BuildPropertyTreesInternal(
       data_for_children.render_target =
           Parent(scroll_child)->effect_tree_index();
       BuildPropertyTreesInternal(scroll_child, data_for_children,
-                                 &data_from_child);
+                                 &data_from_child, build_new_clip_tree);
       data_to_parent->Merge(data_from_child);
     }
   }
@@ -1360,7 +1440,8 @@ void BuildPropertyTreesTopLevelInternal(
     const gfx::Rect& viewport,
     const gfx::Transform& device_transform,
     PropertyTrees* property_trees,
-    SkColor color) {
+    SkColor color,
+    bool build_new_clip_tree) {
   if (!property_trees->needs_rebuild) {
     draw_property_utils::UpdatePageScaleFactor(
         property_trees, page_scale_layer, page_scale_factor,
@@ -1423,7 +1504,8 @@ void BuildPropertyTreesTopLevelInternal(
           root_clip, kRootPropertyTreeNodeId);
 
   DataForRecursionFromChild<LayerType> data_from_child;
-  BuildPropertyTreesInternal(root_layer, data_for_recursion, &data_from_child);
+  BuildPropertyTreesInternal(root_layer, data_for_recursion, &data_from_child,
+      build_new_clip_tree);
   property_trees->needs_rebuild = false;
 
   // The transform tree is kept up to date as it is built, but the
@@ -1467,7 +1549,8 @@ void PropertyTreeBuilder::BuildPropertyTrees(
     float device_scale_factor,
     const gfx::Rect& viewport,
     const gfx::Transform& device_transform,
-    PropertyTrees* property_trees) {
+    PropertyTrees* property_trees,
+    bool build_new_clip_tree) {
   property_trees->is_main_thread = true;
   property_trees->is_active = false;
   SkColor color = root_layer->GetLayerTree()->background_color();
@@ -1477,7 +1560,7 @@ void PropertyTreeBuilder::BuildPropertyTrees(
       root_layer, page_scale_layer, inner_viewport_scroll_layer,
       outer_viewport_scroll_layer, overscroll_elasticity_layer,
       elastic_overscroll, page_scale_factor, device_scale_factor, viewport,
-      device_transform, property_trees, color);
+      device_transform, property_trees, color, build_new_clip_tree);
 #if DCHECK_IS_ON()
   for (auto* layer : *root_layer->GetLayerTree())
     CheckScrollAndClipPointersForLayer(layer);
@@ -1496,7 +1579,8 @@ void PropertyTreeBuilder::BuildPropertyTrees(
     float device_scale_factor,
     const gfx::Rect& viewport,
     const gfx::Transform& device_transform,
-    PropertyTrees* property_trees) {
+    PropertyTrees* property_trees,
+    bool build_new_clip_tree) {
   property_trees->is_main_thread = false;
   property_trees->is_active = root_layer->IsActive();
   SkColor color = root_layer->layer_tree_impl()->background_color();
@@ -1506,7 +1590,7 @@ void PropertyTreeBuilder::BuildPropertyTrees(
       root_layer, page_scale_layer, inner_viewport_scroll_layer,
       outer_viewport_scroll_layer, overscroll_elasticity_layer,
       elastic_overscroll, page_scale_factor, device_scale_factor, viewport,
-      device_transform, property_trees, color);
+      device_transform, property_trees, color, build_new_clip_tree);
   property_trees->ResetCachedData();
 }