Handle nested position:sticky elements correctly (compositor)

cc/trees/property_tree_builder.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/property_tree_builder.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <set>
@@ skipping 495 matching lines @@
 }
 
 static inline bool ShouldFlattenTransform(Layer* layer) {
   return layer->should_flatten_transform();
 }
 
 static inline bool ShouldFlattenTransform(LayerImpl* layer) {
   return layer->test_properties()->should_flatten_transform;
 }
 
+static inline gfx::Vector2dF CalculateTotalStickyOffsetToScroller(
+    LayerImpl* layer,
+    int scroll_ancestor_layer_id) {
+  NOTREACHED();
+  return gfx::Vector2dF();
+}
+
+static inline gfx::Vector2dF CalculateTotalStickyOffsetToScroller(
+    Layer* layer,
+    int scroll_ancestor_layer_id) {
+  return draw_property_utils::CalculateTotalStickyOffsetToScroller(
+      layer, scroll_ancestor_layer_id);
+}
+
 template <typename LayerType>
 bool AddTransformNodeIfNeeded(
     const DataForRecursion<LayerType>& data_from_ancestor,
     LayerType* layer,
     bool created_render_surface,
     DataForRecursion<LayerType>* data_for_children) {
   const bool is_root = !Parent(layer);
   const bool is_page_scale_layer = layer == data_from_ancestor.page_scale_layer;
   const bool is_overscroll_elasticity_layer =
       layer == data_from_ancestor.overscroll_elasticity_layer;
@@ skipping 226 matching lines @@
       // viewport bounds change, but do not unconditionally move by that delta
       // like fixed position nodes.
       if (scroll_ancestor->scrolls_inner_viewport) {
         data_for_children->property_trees->transform_tree
             .AddNodeAffectedByInnerViewportBoundsDelta(node->id);
       } else if (scroll_ancestor->scrolls_outer_viewport) {
         data_for_children->property_trees->transform_tree
             .AddNodeAffectedByOuterViewportBoundsDelta(node->id);
       }
     }
-    sticky_data->main_thread_offset =
-        layer->position().OffsetFromOrigin() -
-        sticky_data->constraints.parent_relative_sticky_box_offset
-            .OffsetFromOrigin();
+    // The sticky box offset calculated in CompositedLayerMapping must be
+    // adjusted for the enclosing layer's sticky offset.
+    gfx::Point sticky_box_offset(
+        sticky_data->constraints.parent_relative_sticky_box_offset);
+    if (Parent(layer)->id() != scroll_ancestor->owning_layer_id) {
+      sticky_box_offset +=
+          gfx::ToFlooredVector2d(CalculateTotalStickyOffsetToScroller(
+              Parent(layer), scroll_ancestor->owning_layer_id));
+    }
+    sticky_data->main_thread_offset = layer->position().OffsetFromOrigin() -
+                                      sticky_box_offset.OffsetFromOrigin();
+    // Copy the ancestor nodes for later use. These layers are guaranteed to
+    // have transform nodes because they are our ancestors and they are sticky.
+    if (Layer* layer =
+            sticky_data->constraints.nearest_layer_shifting_sticky_box) {
+      sticky_data->nearest_node_shifting_sticky_box =
+          layer->transform_tree_index();
+    }
+    if (Layer* layer =
+            sticky_data->constraints.nearest_layer_shifting_containing_block) {
+      sticky_data->nearest_node_shifting_containing_block =
+          layer->transform_tree_index();
+    }
   }
 
   node->needs_local_transform_update = true;
   data_from_ancestor.property_trees->transform_tree.UpdateTransforms(node->id);
 
   layer->set_offset_to_transform_parent(gfx::Vector2dF());
 
   // Flattening (if needed) will be handled by |node|.
   layer->set_should_flatten_transform_from_property_tree(false);
 
@@ skipping 771 matching lines @@
       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);
   property_trees->effect_tree.CreateOrReuseRenderSurfaces(
       &render_surfaces, root_layer->layer_tree_impl());
   property_trees->ResetCachedData();
 }
 
 }  // namespace cc