Handle nested position:sticky elements correctly (compositor)

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 04fa7f4a4236956fa9657f1ed3ae28b0479c252c..a94cb99798a0e18d7f7441a6ebe488d210cae5b8 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -29,6 +29,7 @@
 #include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/mutable_properties.h"
 #include "cc/trees/mutator_host.h"
+#include "cc/trees/scroll_node.h"
 #include "cc/trees/transform_node.h"
 #include "third_party/skia/include/core/SkImageFilter.h"
 #include "ui/gfx/geometry/rect_conversions.h"
@@ -590,10 +591,32 @@ void Layer::SetPosition(const gfx::PointF& position) {
       StickyPositionNodeData* sticky_data =
           property_trees->transform_tree.StickyPositionData(
               transform_tree_index());
+      // The sticky box offset calculated in CompositedLayerMapping must be
+      // adjusted for the enclosing layers sticky offset.
+      // TODO(smcgruer): We may want to do this blink side instead like the
+      // scroll.

[flackr, 2017/03/09 20:22:08]

Unless we add a data channel for updating this (similar to updating the layer
position), I don't think we can pass this extra data from the blink side right
now. so it does make sense to do here.

[smcgruer, 2017/03/14 22:04:05]

Acknowledged.

+      gfx::Point sticky_box_offset(
+          sticky_data->constraints.parent_relative_sticky_box_offset);
+      ScrollNode* scroll_ancestor =
+          property_trees->scroll_tree.Node(scroll_tree_index());
+      if (parent()->id() != scroll_ancestor->owning_layer_id) {
+        sticky_box_offset += gfx::ToFlooredVector2d(
+            draw_property_utils::CalculateTotalStickyOffsetToScroller(
+                parent(), scroll_ancestor->owning_layer_id));
+      }
       sticky_data->main_thread_offset =
-          position.OffsetFromOrigin() -
-          sticky_data->constraints.parent_relative_sticky_box_offset
-              .OffsetFromOrigin();
+          position.OffsetFromOrigin() - sticky_box_offset.OffsetFromOrigin();
+      // Set the ancestor nodes for later use in the property tree.
+      if (Layer* layer =
+              sticky_data->constraints.nearest_layer_shifting_sticky_box) {
+        sticky_data->nearest_node_shifting_sticky_box =
+            layer->transform_tree_index();

[flackr, 2017/03/09 20:22:08]

I don't understand this, do the constraints or the indices on the node change
without rebuilding the property trees? My understanding was that they are static
until we build a new tree.

[smcgruer, 2017/03/14 22:04:05]

It was mostly just copy/paste. Removed.

+      }
+      if (Layer* layer = sticky_data->constraints
+                             .nearest_layer_shifting_containing_block) {
+        sticky_data->nearest_node_shifting_containing_block =
+            layer->transform_tree_index();
+      }
     }
     transform_node->needs_local_transform_update = true;
     transform_node->transform_changed = true;