Implement HitTestAggregator

components/viz/service/hit_test/hit_test_aggregator.h

Index: components/viz/service/hit_test/hit_test_aggregator.h
diff --git a/components/viz/service/hit_test/hit_test_aggregator.h b/components/viz/service/hit_test/hit_test_aggregator.h
new file mode 100644
index 0000000000000000000000000000000000000000..79338be7303333f9e16c0be3abcf5bc37724177c
--- /dev/null
+++ b/components/viz/service/hit_test/hit_test_aggregator.h
@@ -0,0 +1,117 @@
+// Copyright 2017 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.
+
+#ifndef COMPONENTS_VIZ_SERVICE_HIT_TEST_HIT_TEST_AGGREGATOR_H_
+#define COMPONENTS_VIZ_SERVICE_HIT_TEST_HIT_TEST_AGGREGATOR_H_
+
+#include "cc/surfaces/surface_id.h"
+#include "cc/surfaces/surface_observer.h"
+#include "components/viz/common/display_hit_test_region.h"
+#include "components/viz/service/viz_service_export.h"
+#include "services/viz/public/interfaces/hit_test_region_list.mojom.h"
+
+namespace viz {
+namespace hit_test {
+
+namespace test {
+class HitTestAggregatorTest;
+}
+
+// HitTestAggregator collects HitTestRegionList objects from surfaces and
+// aggregates them into a DisplayHitTesData structue made available in
+// shared memory to enable efficient hit testing across processes.
+//
+// This is intended to be created in the viz or GPU process. For mus+ash this
+// will be true after the mus process split.
+
+class VIZ_SERVICE_EXPORT HitTestAggregator : public cc::SurfaceObserver {
+ public:
+  HitTestAggregator();
+  ~HitTestAggregator();
+
+  // Called when HitTestRegionList is submitted along with every call
+  // to SubmitCompositorFrame.  This is collected in pending_ until
+  // surfaces are aggregated and put on the display.
+  void SubmitHitTestRegionList(
+      hit_test::mojom::HitTestRegionListPtr hit_test_region_list);
+
+  // Called after surfaces have been aggregated into the DisplayFrame.
+  // In this call HitTestRegionList structures received from active surfaces
+  // are aggregated into the DisplayHitTestRegionList structure in
+  // shared memory used for event targetting.
+  void Aggregate(cc::SurfaceId display_surface_id);
+
+  // Performs the work of Aggregate by creating a PostTask so that
+  // the work is not directly on the call.
+  void PostTaskAggregate(cc::SurfaceId display_surface_id);
+
+  // Called at BeginFrame. Swaps buffers in shared memory.
+  void Swap();
+
+ private:
+  friend class test::HitTestAggregatorTest;
+
+  // Allocates memory for the DisplayHitTestRegionList Structure.
+  void AllocateDisplayHitTestRegionList();
+  void AllocateDisplayHitTestRegionList(int length);
+
+  // Appends the root element to the DisplayHitTestRegionList structure.
+  void AppendRoot(cc::SurfaceId surface_id);
+
+  // Appends a region to the DisplayHitTestRegionList structure to recursively
+  // build the tree.
+  int AppendRegion(DisplayHitTestRegion* regions,
+                   const hit_test::mojom::HitTestRegionPtr& region,
+                   int index);
+
+  // cc:SurfaceObserver:

[varkha, 2017/06/28 19:47:05]

nit: add ':' in "cc::SurfaceObserver:"

[gklassen, 2017/06/29 11:56:26]

Done.

+  void OnSurfaceCreated(const cc::SurfaceInfo& surface_info) override {}
+  void OnSurfaceDestroyed(const cc::SurfaceId& surface_id) override {}
+  bool OnSurfaceDamaged(const cc::SurfaceId& surface_id,
+                        const cc::BeginFrameAck& ack) override;
+  void OnSurfaceDiscarded(const cc::SurfaceId& surface_id) override;
+  void OnSurfaceDamageExpected(const cc::SurfaceId& surface_id,
+                               const cc::BeginFrameArgs& args) override {}
+
+  // Called when a surface has been aggregated and added to the
+  // display frame.  HitTestRegionList objects are held but ignored until
+  // this happens.  HitTestRegionList for the surface is copied from |pending_|
+  // to |active_| in this method.
+  void OnSurfaceWillDraw(const cc::SurfaceId& surface_id) override;
+
+  using HitTestRegionListMap =
+      std::map<cc::SurfaceId, hit_test::mojom::HitTestRegionListPtr>;
+
+  // The collection of received HitTestRegionList objects that have not yet
+  // been added to the DisplayFrame (OnSurfaceWillDraw has not been called).
+  HitTestRegionListMap pending_;
+
+  // The collection of HitTestRegionList objects that have been added to the
+  // DisplayFrame (OnSurfaceWillDraw has been called).
+  HitTestRegionListMap active_;
+
+  // Keeps track of the number of regions in the active list
+  // so that we know when we exceed the available length.
+  int active_region_count_;
+
+  mojo::ScopedSharedBufferHandle read_handle_;
+  mojo::ScopedSharedBufferHandle write_handle_;
+
+  int read_size_;
+  int write_size_;

[sadrul, 2017/06/28 20:30:12]

Please document the size is the number of elements in the array, not the number
of bytes.

[varkha, 2017/06/28 21:22:00]

Maybe consider a self-descriptive variable name as well although not sure what
would
work the best. Maybe read_elements_count_ / write_elements_count_

[gklassen, 2017/06/29 11:56:26]

Acknowledged.  I've commented but kept the use of the term size because it seems
to follow the convention used in vector and other std collections.  Sound ok?

[gklassen, 2017/06/29 11:56:26]

Done.

+
+  mojo::ScopedSharedBufferMapping read_buffer_;
+  mojo::ScopedSharedBufferMapping write_buffer_;
+
+  // Handles the case when this object is deleted after
+  // the PostTaskAggregation call is scheduled but before invocation.
+  base::WeakPtrFactory<HitTestAggregator> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(HitTestAggregator);
+};
+
+}  // namespace hit_test
+}  // namespace viz
+
+#endif  // COMPONENTS_VIZ_SERVICE_HIT_TEST_HIT_TEST_AGGREGATOR_H_