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 622894949aca12fb11f1604c9593ff5ee45130d4..2ddbcd26611d55f69e8f9ee2877f80cf22cef265 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 +43,30 @@
 
 namespace cc {
 
+namespace {
+
+const uint32_t kMainLayerFlags =

[enne (OOO), 2015/11/16 19:12:33]

What does "main" here mean?

[Ian Vollick, 2015/11/18 17:20:33]

Added comments in the header. It's analogous to m_graphicsLayer in CLM. I
couldn't think of a better name -- if you have a suggestion I would gladly take
it :)

+    kMutablePropertyOpacity | kMutablePropertyTransform;
+const uint32_t kScrollLayerFlags =
+    kMutablePropertyScrollLeft | kMutablePropertyScrollTop;
+const uint32_t kMainLayerIndex = 0;

[enne (OOO), 2015/11/16 19:12:33]

Do you expect to have more layer types? It looks a bit odd to have constant
indices when n=2.

[Ian Vollick, 2015/11/18 17:20:33]

It is odd. The whole ElementLayers class was wonky and I don't know what
possessed me to write it the way I did. I've switched it to a POD struct with
two named pointers.

+const uint32_t kScrollLayerIndex = 1;
+
+}  // namespace
+
+class ElementLayers {
+ public:
+  ElementLayers() {
+    layers[0] = nullptr;
+    layers[1] = nullptr;
+  }
+  LayerImpl*& main() { return layers[kMainLayerIndex]; }
+  LayerImpl*& scroll() { return layers[kScrollLayerIndex]; }
+
+ private:
+  LayerImpl* layers[2];

[esprehn, 2015/11/16 20:01:04]

just add two members, why use an array? Also this thing seems like it just wants
public fields, no reason to have getters at all

[Ian Vollick, 2015/11/18 17:20:33]

Agreed. Updated.

+};
+
 LayerTreeImpl::LayerTreeImpl(
     LayerTreeHostImpl* layer_tree_host_impl,
     scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
@@ -353,6 +378,49 @@ 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()];
+  if (layer->mutable_properties() & kMainLayerFlags) {
+    if (!layers.main() || layer->IsActive())
+      layers.main() = layer;

[esprehn, 2015/11/16 20:01:04]

this is very weird, why not just make the fields public or have a setter?

[Ian Vollick, 2015/11/18 17:20:33]

Done.

+  }
+  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()];
+  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());
+}
+
+bool LayerTreeImpl::GetMutableLayers(uint64_t element_id,
+                                     LayerImpl** main_layer,
+                                     LayerImpl** scroll_layer) {
+  auto iter = element_layers_map_.find(element_id);
+  if (iter == element_layers_map_.end())
+    return false;
+
+  *main_layer = iter->second.main();
+  *scroll_layer = iter->second.scroll();

[esprehn, 2015/11/16 20:01:04]

just return the ElementLayers object by value, it's just two pointers. No need
for the out params. Callers can null check the ElementLayers object

[Ian Vollick, 2015/11/18 17:20:33]

Done.

+  return true;
+}
 
 LayerImpl* LayerTreeImpl::InnerViewportContainerLayer() const {
   return InnerViewportScrollLayer()