compositor-worker: Introduce WebCompositorMutableState

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 9fbd1189ca553215e4200b85ca55591ef8806d3c..37cbd4f5c6abd58692651fc49c7de02cd9a74461 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -14,6 +14,7 @@
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/animation/animation_host.h"
 #include "cc/animation/keyframed_animation_curve.h"
+#include "cc/animation/mutable_properties.h"
 #include "cc/animation/scrollbar_animation_controller.h"
 #include "cc/animation/scrollbar_animation_controller_linear_fade.h"
 #include "cc/animation/scrollbar_animation_controller_thinning.h"
@@ -42,6 +43,15 @@
 
 namespace cc {
 
+namespace {
+
+const uint32_t kMainLayerFlags =
+    kMutablePropertyOpacity | kMutablePropertyTransform;
+const uint32_t kScrollLayerFlags =
+    kMutablePropertyScrollLeft | kMutablePropertyScrollTop;
+
+}  // namespace
+
 LayerTreeImpl::LayerTreeImpl(
     LayerTreeHostImpl* layer_tree_host_impl,
     scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
@@ -353,6 +363,46 @@ void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
 
   target_tree->has_ever_been_drawn_ = false;
 }
+void LayerTreeImpl::AddToElementMap(LayerImpl* layer) {
+  TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("compositor-worker"),
+               "LayerTreeImpl::AddToElementMap", "element_id",
+               layer->element_id(), "layer_id", layer->id());
+  ElementLayers& layers = element_layers_map_[layer->element_id()];

[esprehn, 2015/12/16 04:01:58]

this puts a new hash lookup for every composited layer, and now every layer is
replicated into this map, so this map is the size of the layer tree, is that
really necessary?

[Ian Vollick, 2015/12/23 17:34:40]

A non-zero element id is actually pretty rare. Before we called this function,
we check that we have a non-zero id, but that wasn't obvious. I've moved these
checks into this function and RemoveFromElementMap, both to ensure that we don't
forget and also for documentation.

+  if (layer->mutable_properties() & kMainLayerFlags) {
+    if (!layers.main || layer->IsActive())
+      layers.main = layer;
+  }
+  if (layer->mutable_properties() & kScrollLayerFlags) {
+    if (!layers.scroll || layer->IsActive()) {
+      TRACE_EVENT2("compositor-worker", "LayerTreeImpl::AddToElementMap scroll",
+                   "element_id", layer->element_id(), "layer_id", layer->id());
+      layers.scroll = layer;
+    }
+  }
+}
+
+void LayerTreeImpl::RemoveFromElementMap(LayerImpl* layer) {
+  TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("compositor-worker"),
+               "LayerTreeImpl::RemoveFromElementMap", "element_id",
+               layer->element_id(), "layer_id", layer->id());
+  ElementLayers& layers = element_layers_map_[layer->element_id()];

[esprehn, 2015/12/16 04:01:58]

and another map lookup for every layer removal

[Ian Vollick, 2015/12/23 17:34:40]

Ditto.

+  if (layer->mutable_properties() & kMainLayerFlags)
+    layers.main = nullptr;
+  if (layer->mutable_properties() & kScrollLayerFlags)
+    layers.scroll = nullptr;
+
+  if (!layers.main && !layers.scroll)
+    element_layers_map_.erase(layer->element_id());
+}
+
+LayerTreeImpl::ElementLayers LayerTreeImpl::GetMutableLayers(
+    uint64_t element_id) {
+  auto iter = element_layers_map_.find(element_id);
+  if (iter == element_layers_map_.end())
+    return ElementLayers();
+
+  return iter->second;
+}
 
 LayerImpl* LayerTreeImpl::InnerViewportContainerLayer() const {
   return InnerViewportScrollLayer()