Implement HitTestAggregator

components/viz/common/hit_test/display_hit_test_data.h

+// 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_COMMON_HIT_TEST_DISPLAY_HIT_TEST_DATA_H_
+#define COMPONENTS_VIZ_COMMON_HIT_TEST_DISPLAY_HIT_TEST_DATA_H_
+
+#include <stdint.h>
+
+#include "cc/surfaces/surface_id.h"
+#include "services/viz/hit_test/public/interfaces/hit_test_data.mojom.h"
+
+namespace viz {
+
+// DiplayHitTestData contains the aggregated hit-test data for the Display.
+//
+// It is designed to be in shared memory so that the viz process can
+// write the hit_test data, and the browser / ws process can read without
+// process hops.
+//
+// One instance of this class contains a double buffer of entries -
+// the viz process will write into one half while client processes read from
+// the other.  read_offset is used to swap buffers atomically.
+
+// A DisplayHitTestRegion element with child_count of kEndOfList indicates
+// the last element ( end of the list ).
+constexpr int kEndOfList = -1;
+
+// A read_offset set to kOldPleaseReAcquire indicates that the buffer has been
+// resized and clients should re-acquire their reference.
+constexpr int kOldPleaseReAcquire = -1;
+
+struct DisplayHitTestRegion {
+  // The frame_sink_id corresponding to this region.  Events that match

[varkha, 2017/06/20 19:56:58]

nit: s/frame_sink_id/cc::FrameSinkId

[gklassen, 2017/06/26 21:55:19]

Done.

+  // are routed to this surface.
+  cc::FrameSinkId frame_sink_id;
+
+  // Flags to indicate the type of region as defined in
+  // services/viz/hit_test/public/interfaces/hit_test_data.mojom.h.
+  uint32_t flags;
+
+  // The rectangle that defines the region.
+  gfx::Rect rect;
+
+  // The transform applied to the rect.
+  gfx::Transform transform;
+
+  // The number of children ( including their children ) below this entry.
+  // If this element is not matched then child_count elements can be skipped
+  // to move to the next entry.
+  int child_count;
+};
+
+struct DisplayHitTestData {
+  int length;
+  base::subtle::Atomic32 read_offset;
+  DisplayHitTestRegion regions[];
+};
+
+}  // namespace viz
+
+#endif  // COMPONENTS_VIZ_COMMON_HIT_TEST_DISPLAY_HIT_TEST_DATA_H_