Implement HitTestAggregator

components/viz/service/hit_test/hit_test_aggregator.cc

Index: components/viz/service/hit_test/hit_test_aggregator.cc
diff --git a/components/viz/service/hit_test/hit_test_aggregator.cc b/components/viz/service/hit_test/hit_test_aggregator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..78ff7b255f91dc13944ba91d956d99b53699b8eb
--- /dev/null
+++ b/components/viz/service/hit_test/hit_test_aggregator.cc
@@ -0,0 +1,197 @@
+// 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/service/hit_test/hit_test_aggregator.h"
+#include "components/viz/common/display_hit_test_data.h"
+
+namespace viz {
+namespace hit_test {
+
+namespace {
+// TODO(gklassen): Review and select appropriate sizes based on
+// telemetry / UMA.
+constexpr int kInitialSize = 1024;
+constexpr int kIncrementalSize = 1024;
+constexpr int kMaxRegionsPerSurface = 1024;
+constexpr int kMaxSize = 100 * 1024;
+
+bool ValidateHitTestRegion(
+    const hit_test::mojom::HitTestRegionPtr& hit_test_region) {
+  if (hit_test_region->flags == hit_test::mojom::kHitTestChildSurface) {
+    if (!hit_test_region->surface_id.is_valid())
+      return false;
+  }
+
+  return true;

[sadrul, 2017/06/28 05:27:40]

This can be just:

  return hit_test_region->flags != hit_test::mojom::kHitTestChildSurface ||
         hit_test_region->surface_id.is_valid();

[gklassen, 2017/06/28 16:29:59]

As we understand better how these will be constructed, I hope and expect that we
will add additional checks for other fields and so I'd like to preserve the
existing structure for readability and extension.  Is that ok?

+}
+bool ValidateHitTestData(const hit_test::mojom::HitTestDataPtr& hit_test_data) {
+  if (hit_test_data->regions.size() > kMaxRegionsPerSurface)
+    return false;
+  for (auto& region : hit_test_data->regions) {
+    if (!ValidateHitTestRegion(region))
+      return false;
+  }
+  return true;
+}
+
+}  // namespace
+
+HitTestAggregator::HitTestAggregator()
+    : active_region_count_(0), weak_ptr_factory_(this) {
+  AllocateDisplayHitTestData();
+}
+HitTestAggregator::~HitTestAggregator() {}
+
+void HitTestAggregator::SubmitHitTestData(
+    hit_test::mojom::HitTestDataPtr hit_test_data) {
+  DCHECK(ValidateHitTestData(hit_test_data));
+  // TODO(gklassen): Runtime validation that hit_test_data is valid.
+  // TODO(gklassen): Inform FrameSink that the hit_test_data is invalid.
+  // TODO(gklassen): FrameSink needs to inform the host of a difficult renderer.
+  pending_[hit_test_data->surface_id] = std::move(hit_test_data);
+}
+
+bool HitTestAggregator::OnSurfaceDamaged(const cc::SurfaceId& surface_id,
+                                         const cc::BeginFrameAck& ack) {
+  return false;
+}
+
+void HitTestAggregator::OnSurfaceDiscarded(const cc::SurfaceId& surface_id) {
+  pending_.erase(surface_id);
+  active_.erase(surface_id);
+}
+
+void HitTestAggregator::OnSurfaceWillDraw(const cc::SurfaceId& surface_id) {
+  auto pending_search = pending_.find(surface_id);
+  if (pending_search == pending_.end()) {
+    // Have already activated pending hit_test_data objects for this surface.
+    return;
+  }
+  hit_test::mojom::HitTestData* hit_test_data = pending_search->second.get();
+
+  // Update the region count.
+  auto active_search = active_.find(surface_id);
+  if (active_search != active_.end()) {
+    hit_test::mojom::HitTestData* old_hit_test_data =
+        active_search->second.get();
+    active_region_count_ -= old_hit_test_data->regions.size();
+  }
+  active_region_count_ += hit_test_data->regions.size();
+  DCHECK_GE(active_region_count_, 0);
+
+  active_[surface_id] = std::move(pending_[surface_id]);
+  pending_.erase(surface_id);
+}
+
+void HitTestAggregator::AllocateDisplayHitTestData() {
+  AllocateDisplayHitTestData(kInitialSize);
+  Swap();
+  AllocateDisplayHitTestData(kInitialSize);
+}
+
+void HitTestAggregator::AllocateDisplayHitTestData(int size) {
+  size_t num_bytes = size * sizeof(DisplayHitTestRegion);
+  write_handle_ = mojo::SharedBufferHandle::Create(num_bytes);
+  write_size_ = size;
+  write_buffer_ = write_handle_->Map(num_bytes);
+
+  DisplayHitTestRegion* region = (DisplayHitTestRegion*)write_buffer_.get();
+  region[0].child_count = kEndOfList;
+}
+
+void HitTestAggregator::PostTaskAggregate(cc::SurfaceId display_surface_id) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE,
+      base::BindOnce(&HitTestAggregator::Aggregate,
+                     weak_ptr_factory_.GetWeakPtr(), display_surface_id));
+}
+
+void HitTestAggregator::Aggregate(cc::SurfaceId display_surface_id) {
+  // Size check.
+  int size = write_size_;
+  int max_size = active_region_count_ + active_.size() + 1;
+  if (max_size > kMaxSize)
+    max_size = kMaxSize;
+
+  if (max_size > size) {
+    size = (1 + max_size / kIncrementalSize) * kIncrementalSize;
+    AllocateDisplayHitTestData(size);
+  }
+
+  AppendRoot(display_surface_id);
+}
+
+void HitTestAggregator::AppendRoot(cc::SurfaceId surface_id) {
+  auto search = active_.find(surface_id);
+  CHECK(search != active_.end());
+
+  hit_test::mojom::HitTestData* hit_test_data = search->second.get();
+
+  DisplayHitTestRegion* regions = (DisplayHitTestRegion*)write_buffer_.get();
+
+  regions[0].frame_sink_id = hit_test_data->surface_id.frame_sink_id();
+  regions[0].flags = hit_test_data->flags;
+  regions[0].rect = hit_test_data->bounds;
+  regions[0].transform = hit_test_data->transform;
+
+  int index = 1;
+  for (auto& region : hit_test_data->regions)
+    index = AppendRegion(regions, region, index);
+
+  DCHECK_GE(index, 1);
+  regions[0].child_count = index - 1;
+  regions[index].child_count = kEndOfList;
+}
+
+int HitTestAggregator::AppendRegion(
+    DisplayHitTestRegion* regions,
+    const hit_test::mojom::HitTestRegionPtr& region,
+    int index) {
+  DisplayHitTestRegion* element = &regions[index];
+
+  element->frame_sink_id = region->surface_id.frame_sink_id();
+  element->flags = region->flags;
+  element->rect = region->rect;
+  element->transform = region->transform;
+
+  int parent_index = index++;
+
+  if (index >= write_size_) {
+    element->child_count = 0;

[sadrul, 2017/06/28 05:27:40]

I think |child_count| gets set to kEndOfList in AppendRoot() after returning? So
maybe just skip this, and add a comment instead?

[gklassen, 2017/06/28 16:29:59]

Done.

+    return parent_index;
+  }
+
+  if (region->flags == hit_test::mojom::kHitTestChildSurface) {
+    auto search = active_.find(region->surface_id);
+    if (search == active_.end()) {
+      // Surface HitTestData not found - it may be late.
+      // Don't include this region so that it doesn't receive events.
+      return parent_index;
+    }
+
+    // Rather than add a node in the tree for this hit_test_data element
+    // we can simplify the tree by merging the flags and transform into
+    // the kHitTestChildSurface element.
+    hit_test::mojom::HitTestData* hit_test_data = search->second.get();
+    if (!hit_test_data->transform.IsIdentity())
+      element->transform.PreconcatTransform(hit_test_data->transform);
+
+    element->flags |= hit_test_data->flags;
+
+    for (auto& child_region : hit_test_data->regions)
+      index = AppendRegion(regions, child_region, index);

[sadrul, 2017/06/28 05:27:40]

Should we break if |index| reaches |write_size_ - 1| at any iteration in this
loop?

[gklassen, 2017/06/28 16:29:59]

Done.

+  }
+  DCHECK_GE(index - parent_index - 1, 0);
+  element->child_count = index - parent_index - 1;
+  return index;
+}
+
+void HitTestAggregator::Swap() {
+  std::swap(read_handle_, write_handle_);
+  std::swap(read_size_, write_size_);
+  std::swap(read_buffer_, write_buffer_);
+}
+
+}  // namespace hit_test
+}  // namespace viz