Avoid exposing cc::Layer tree to CompositorProxy

third_party/WebKit/Source/platform/graphics/CompositorMutatorClient.cpp

Index: third_party/WebKit/Source/platform/graphics/CompositorMutatorClient.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/CompositorMutatorClient.cpp b/third_party/WebKit/Source/platform/graphics/CompositorMutatorClient.cpp
index 3909529da4e469c11eaf9e72f110b48a52cb6b26..1b33091563c8adcc44e0dff367d3b974999e117d 100644
--- a/third_party/WebKit/Source/platform/graphics/CompositorMutatorClient.cpp
+++ b/third_party/WebKit/Source/platform/graphics/CompositorMutatorClient.cpp
@@ -5,10 +5,13 @@
 #include "platform/graphics/CompositorMutatorClient.h"
 
 #include <memory>
+
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/trace_event/trace_event.h"
 #include "cc/trees/layer_tree_impl.h"
+#include "cc/trees/scroll_node.h"
+#include "platform/graphics/CompositorElementId.h"
 #include "platform/graphics/CompositorMutableStateProvider.h"
 #include "platform/graphics/CompositorMutation.h"
 #include "platform/graphics/CompositorMutationsTarget.h"
@@ -39,9 +42,26 @@ bool CompositorMutatorClient::Mutate(base::TimeTicks monotonic_time,
   double monotonic_time_now = (monotonic_time - base::TimeTicks()).InSecondsF();
   if (!mutations_)
     mutations_ = WTF::WrapUnique(new CompositorMutations);
-  CompositorMutableStateProvider compositor_state(tree_impl, mutations_.get());
+
+  ProxyCompositorMutablePropertiesMap input_properties_map;
+  SnapshotLayerTree(tree_impl, &input_properties_map);
+
+  CompositorMutations new_mutations;
+  CompositorMutableStateProvider compositor_state(&input_properties_map,
+                                                  &new_mutations);
   bool should_reinvoke =
       mutator_->Mutate(monotonic_time_now, &compositor_state);
+
+  for (const auto& entry : new_mutations.map) {
+    UpdateLayerTree(tree_impl, entry.key, entry.value.get());
+  }
+
+  // CompositorMutation objects are moved to updateMutations rather than copied
+  // to reduce the number of allocated objects.
+  for (auto& entry : new_mutations.map) {
+    UpdateMutations(entry.key, std::move(entry.value));
+  }
+
   return should_reinvoke;
 }
 
@@ -67,9 +87,153 @@ void CompositorMutatorClient::SetNeedsMutate() {
   client_->SetNeedsMutate();
 }
 
+void CompositorMutatorClient::RegisterCompositorProxy(
+    uint64_t proxy_id,
+    uint64_t element_id,
+    uint32_t mutable_properties) {
+  TRACE_EVENT0("compositor-worker",
+               "CompositorMutatorClient::RegisterCompositorProxy");
+  input_properties_[proxy_id] = std::make_pair(element_id, mutable_properties);
+}
+
+void CompositorMutatorClient::UnregisterCompositorProxy(uint64_t proxy_id) {
+  TRACE_EVENT0("compositor-worker",
+               "CompositorMutatorClient::UnregisterCompositorProxy");
+  DCHECK(input_properties_.find(proxy_id) != input_properties_.end());
+  input_properties_.erase(proxy_id);
+}
+
 void CompositorMutatorClient::SetMutationsForTesting(
     std::unique_ptr<CompositorMutations> mutations) {
   mutations_ = std::move(mutations);
 }
 
+void CompositorMutatorClient::SnapshotLayerTree(
+    const cc::LayerTreeImpl* tree_impl,
+    ProxyCompositorMutablePropertiesMap* input_map) const {
+  ProxyCompositorMutablePropertiesMap& input_map_ref = *input_map;
+  for (const auto& it : input_properties_) {
+    uint64_t proxy_id = it.first;
+    const std::pair<uint64_t, uint32_t>& value = it.second;
+    uint64_t element_id = value.first;
+    uint32_t properties = value.second;
+
+    // Avoid expensive layer lookups by first checking whether any properties
+    // are being mutated that require that layer.
+    cc::LayerImpl* layer = nullptr;
+    cc::LayerImpl* scrollLayer = nullptr;
+    if (properties & (CompositorMutableProperty::kOpacity |
+                      CompositorMutableProperty::kTransform)) {
+      layer = tree_impl->LayerByElementId(CreateCompositorElementId(
+          element_id, CompositorSubElementId::kPrimary));
+    }
+    if (properties & (CompositorMutableProperty::kScrollLeft |
+                      CompositorMutableProperty::kScrollTop)) {
+      scrollLayer = tree_impl->LayerByElementId(CreateCompositorElementId(
+          element_id, CompositorSubElementId::kScroll));
+    }
+
+    // If the element no longer exists in the layer tree, there is no point
+    // creating an entry for it.
+    // TODO(smcgruer): Should we just create a default entry instead?
+    if (!layer && !scrollLayer)
+      continue;
+
+    input_map_ref[proxy_id].element_id = element_id;
+    input_map_ref[proxy_id].transform = SkMatrix44::I();
+    if (layer) {
+      if (properties & CompositorMutableProperty::kOpacity) {
+        input_map_ref[proxy_id].opacity = layer->Opacity();
+      }
+      if (properties & CompositorMutableProperty::kTransform) {
+        input_map_ref[proxy_id].transform = layer->Transform().matrix();
+      }
+    }
+    if (scrollLayer) {
+      if (properties & CompositorMutableProperty::kScrollLeft) {
+        input_map_ref[proxy_id].scroll_left =
+            scrollLayer->CurrentScrollOffset().x();
+      }
+      if (properties & CompositorMutableProperty::kScrollTop) {
+        input_map_ref[proxy_id].scroll_top =
+            scrollLayer->CurrentScrollOffset().y();
+      }
+    }
+  }
+}
+
+void CompositorMutatorClient::UpdateLayerTree(
+    cc::LayerTreeImpl* tree_impl,
+    uint64_t element_id,
+    const CompositorMutation* mutation) {
+  uint32_t mutatedProperties = mutation->mutatedProperties();
+
+  // Avoid expensive layer lookups by checking first whether any relevant
+  // properties have been mutated.
+  if (mutatedProperties & (CompositorMutableProperty::kOpacity |
+                           CompositorMutableProperty::kTransform)) {
+    cc::ElementId compositor_element_id =
+        CreateCompositorElementId(element_id, CompositorSubElementId::kPrimary);
+    cc::LayerImpl* layer = tree_impl->LayerByElementId(compositor_element_id);
+    if (layer) {
+      if (mutatedProperties & CompositorMutableProperty::kOpacity) {
+        tree_impl->SetOpacityMutated(compositor_element_id,
+                                     mutation->Opacity());
+      }
+      if (mutatedProperties & CompositorMutableProperty::kTransform) {
+        tree_impl->SetTransformMutated(compositor_element_id,
+                                       gfx::Transform(mutation->Transform()));
+      }
+    }
+  }
+
+  if (mutatedProperties & (CompositorMutableProperty::kScrollLeft |
+                           CompositorMutableProperty::kScrollTop)) {
+    cc::LayerImpl* scrollLayer = tree_impl->LayerByElementId(
+        CreateCompositorElementId(element_id, CompositorSubElementId::kScroll));
+    if (scrollLayer) {
+      gfx::ScrollOffset offset = scrollLayer->CurrentScrollOffset();
+      if (mutatedProperties & CompositorMutableProperty::kScrollLeft) {
+        offset.set_x(mutation->ScrollLeft());
+      }
+      if (mutatedProperties & CompositorMutableProperty::kScrollTop) {
+        offset.set_y(mutation->ScrollTop());
+      }
+      tree_impl->property_trees()->scroll_tree.OnScrollOffsetAnimated(
+          scrollLayer->id(), scrollLayer->scroll_tree_index(), offset,
+          tree_impl);
+
+      // ScrollTree:OnScrollOffsetAnimated triggers a synchronous main frame
+      // begin that calls TakeMutations and causes mutations_ to be released.
+      // Restore mutations_ for the later call to |updateMutations|.
+      // TODO(smcgruer): Find a way to avoid triggering a main frame begin here.
+      DCHECK(!mutations_);
+      mutations_ = WTF::WrapUnique(new CompositorMutations);
+    }
+  }
+}
+
+void CompositorMutatorClient::UpdateMutations(
+    uint64_t element_id,
+    std::unique_ptr<CompositorMutation> mutation) {
+  if (!mutations_->map.Contains(element_id)) {
+    mutations_->map.Set(element_id, std::move(mutation));
+    return;
+  }
+
+  CompositorMutation* existingMutation = mutations_->map.at(element_id);
+  if (mutation->IsOpacityMutated()) {
+    existingMutation->SetOpacity(mutation->Opacity());
+  }
+  if (mutation->IsTransformMutated()) {
+    existingMutation->SetTransform(mutation->Transform());
+  }
+  if (mutation->IsScrollTopMutated()) {
+    existingMutation->SetScrollTop(mutation->ScrollTop());
+  }
+  if (mutation->IsScrollLeftMutated()) {
+    existingMutation->SetScrollLeft(mutation->ScrollLeft());
+  }
+}
+
 }  // namespace blink