Handle nested position:sticky elements correctly (compositor)

cc/layers/layer.cc

 // Copyright 2010 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/layers/layer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 11 matching lines @@
 #include "cc/layers/layer_impl.h"
 #include "cc/layers/scrollbar_layer_interface.h"
 #include "cc/output/copy_output_request.h"
 #include "cc/output/copy_output_result.h"
 #include "cc/trees/draw_property_utils.h"
 #include "cc/trees/effect_node.h"
 #include "cc/trees/layer_tree_host.h"
 #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"
 #include "ui/gfx/geometry/vector2d_conversions.h"
 
 namespace cc {
 
 base::StaticAtomicSequenceNumber g_next_layer_id;
 
 Layer::Inputs::Inputs(int layer_id)
@@ skipping 541 matching lines @@
                                        id())) {
     DCHECK_EQ(transform_tree_index(),
               property_trees->layer_id_to_transform_node_index[id()]);
     TransformNode* transform_node =
         property_trees->transform_tree.Node(transform_tree_index());
     transform_node->update_post_local_transform(position, transform_origin());
     if (transform_node->sticky_position_constraint_id >= 0) {
       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;
     layer_tree_host_->property_trees()->transform_tree.set_needs_update(true);
     SetNeedsCommitNoRebuild();
     return;
   }
 
   SetNeedsCommit();
 }
@@ skipping 923 matching lines @@
       ->num_copy_requests_in_subtree;
 }
 
 gfx::Transform Layer::screen_space_transform() const {
   DCHECK_NE(transform_tree_index_, TransformTree::kInvalidNodeId);
   return draw_property_utils::ScreenSpaceTransform(
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
 }  // namespace cc