Add viz-host HitTestQuery.

components/viz/host/hit_test/hit_test_query.cc

+// 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.
+
+#include "components/viz/host/hit_test/hit_test_query.h"
+
+namespace viz {
+namespace hit_test {
+
+HitTestQuery::HitTestQuery() {}
+
+HitTestQuery::~HitTestQuery() {}
+
+Target HitTestQuery::FindTargetForLocation(const gfx::Point& location_in_root) {
+  // TODO(riajiang): Assumptions I'm making about the list of DisplayHitTestData
+  // 1. The list is in descending (back to front) z-order.
+  // 2. Children regions have their own FrameSinkId, but those that are just
+  // bounding boxes have the FrameSinkId of their parent.
+  // 3. Children count includes children of children.
+  // 4. After applying transform to the incoming point, point is in the same
+  // coordinate system as the bounds it is comparing against.
+  // For example,
+  //  +e-------------+
+  //  |   +c---------|
+  //  | 1 |+a--+     |
+  //  |   || 2 |     |
+  //  |   |+b--------|
+  //  |   ||         |
+  //  |   ||   3     |
+  //  +--------------+
+  // In this case, after applying identity transform, 1 is in the coordinate
+  // system of e; apply the transfrom-from-e-to-c and transform-from-c-to-a
+  // then we get 2 in the coordinate system of a; apply the
+  // transfrom-from-e-to-c and transform-from-c-to-b then we get 3 in the
+  // coordinate system of b.
+  // 5. Transform contains transform for the position.
+  // 6. HIT_TEST_MINE means the region can receive events, i.e., not just a
+  // bounding box.
+  DCHECK(!display_hit_test_data_list_.empty());
+  Target confirmed_target_so_far;
+  Target tentative_target_so_far;
+  tentative_target_so_far.location_in_target = location_in_root;
+
+  for (DisplayHitTestData::const_iterator it =
+           display_hit_test_data_list_.begin();
+       it != display_hit_test_data_list_.end(); ++it) {

[sadrul, 2017/06/16 17:09:51]

Use for (const auto& region : display_hit_test_data_list_) { ... }

+    gfx::Point location(tentative_target_so_far.location_in_target);
+    if (!it->transform.IsIdentity())
+      it->transform.TransformPoint(&location);
+    if (it->bounds.Contains(location)) {
+      tentative_target_so_far.id = it->id;
+      tentative_target_so_far.location_in_target = location;
+      tentative_target_so_far.flags = it->flags;
+      // TODO(riajiang): Check properly once HitTestRegionFlags is well defined
+      // after https://codereview.chromium.org/2908783002/.
+      // HIT_TEST_MINE is set to be true, which means it can receive events.

[sadrul, 2017/06/16 17:09:51]

I would be OK with starting with a different set of flags in this CL. We can
merge once both CLs are landed. But we don't need to block on the other CL in my
opinion.

+      if (it->flags)
+        confirmed_target_so_far = tentative_target_so_far;

[sadrul, 2017/06/16 17:09:51]

It's not clear to me yet how kHitTestIgnore flag would be used here.

[riajiang, 2017/06/23 02:46:36]

If it's kHitTestIgnore, then that child cannot receive any events (just a
bounding box).

+      if (!it->child_count)
+        break;
+    } else {
+      it += it->child_count;
+    }
+  }
+  return confirmed_target_so_far;
+}
+
+}  // namespace hit_test
+}  // namespace viz