cc: Fix hit-testing in zero-opacity layers.

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index 4095900fae18f839190a3d35ae01406e4a6cd6c4..73ce1d2257898375eb81a007a4725de61d37ecb5 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -63,6 +63,12 @@ static gfx::Vector2dF GetEffectiveTotalScrollOffset(LayerType* layer) {
   return offset;
 }
 
+template <typename LayerType>
+static inline bool LayerCanAcceptInput(LayerType* layer) {

[enne (OOO), 2013/10/29 23:54:22]

Maybe call this LayerHasEventHandler to be consistent?

[sadrul, 2013/10/30 15:44:42]

Done.

+  return !layer->touch_event_handler_region().IsEmpty() ||
+         layer->have_wheel_event_handlers();
+}
+
 inline gfx::Rect CalculateVisibleRectWithCachedLayerRect(
     gfx::Rect target_surface_rect,
     gfx::Rect layer_bound_rect,
@@ -437,10 +443,11 @@ static bool LayerShouldBeSkipped(LayerType* layer,
                                  bool layer_is_visible) {
   // Layers can be skipped if any of these conditions are met.
   //   - is not visible due to it or one of its ancestors being hidden.
+  //   - the layer itself and none of its descendants participate in hit testing
   //   - has empty bounds
   //   - the layer is not double-sided, but its back face is visible.
   //   - is transparent
-  //   - does not draw content and does not participate in hit testing.
+  //   - does not draw content
   //
   // Some additional conditions need to be computed at a later point after the
   // recursion is finished.
@@ -454,6 +461,9 @@ static bool LayerShouldBeSkipped(LayerType* layer,
   if (!layer_is_visible)
     return true;
 
+  if (layer->draw_properties().layer_or_descendant_has_event_handler)

[enne (OOO), 2013/10/29 23:54:22]

I don't think this is sufficient.  I feel like what I said in comment #24 is the
right way to go about this.

As you are processing layers recursively, there is a point of no return after
which all layers must be processed.  If you ever:
    * process a layer with a touch handler
    * process a layer that creates a 3d context with a touch handler descendant.
...then after that point no layer or subtree should be skipped for opacity
reasons.

(Are there other properties other than opacity that need to be considered? Can a
backfacing layer block input?)

Prior to that point of no return, no subtree with a touch handler descendant or
layer with a touch handler should be skipped.

[sadrul, 2013/10/30 05:20:21]

I am using DataForRecursion::subtree_has_event_handler to keep track of whether
a layer is part of a subtree that has a layer with an event handler. When
|subtree_has_event_handler| is set, the call to LayerShouldBeSkipped() or
SubtreeShouldBeSkipped() aren't made at all. So, essentially, no layer/subtree
in the entire tree is skipped when there is any layer that handles touch/wheel
events.

To explain with an example:

 Root
 +---> L1
 |     +----> L2
 +---> L3

L1 has opacity zero, L3 has an event handler. In this case, neither L1 nor L2
are skipped.

I may have misunderstood, but I believe this is what we want?

+    return false;
+
   if (layer->bounds().IsEmpty())
     return true;
 
@@ -471,11 +481,8 @@ static bool LayerShouldBeSkipped(LayerType* layer,
       IsLayerBackFaceVisible(backface_test_layer))
     return true;
 
-  // The layer is visible to events.  If it's subject to hit testing, then
-  // we can't skip it.
-  bool can_accept_input = !layer->touch_event_handler_region().IsEmpty() ||
-      layer->have_wheel_event_handlers();
-  if (!layer->DrawsContent() && !can_accept_input)
+  // The layer is visible to events.
+  if (!layer->DrawsContent())
     return true;
 
   return false;
@@ -498,10 +505,12 @@ static inline bool SubtreeShouldBeSkipped(LayerImpl* layer,
   if (layer->layer_tree_impl()->IsPendingTree() && layer->OpacityIsAnimating())
     return false;
 
+  if (layer->draw_properties().layer_or_descendant_has_event_handler)
+    return false;
+
   // The opacity of a layer always applies to its children (either implicitly
   // via a render surface or explicitly if the parent preserves 3D), so the
   // entire subtree can be skipped if this layer is fully transparent.
-  // TODO(sad): Don't skip layers used for hit testing crbug.com/295295.
   return !layer->opacity();
 }
 
@@ -516,13 +525,15 @@ static inline bool SubtreeShouldBeSkipped(Layer* layer,
   if (!layer_is_visible)
     return true;
 
+  if (layer->draw_properties().layer_or_descendant_has_event_handler)
+    return false;
+
   // If the opacity is being animated then the opacity on the main thread is
   // unreliable (since the impl thread may be using a different opacity), so it
   // should not be trusted.
   // In particular, it should not cause the subtree to be skipped.
   // Similarly, for layers that might animate opacity using an impl-only
   // animation, their subtree should also not be skipped.
-  // TODO(sad): Don't skip layers used for hit testing crbug.com/295295.
   return !layer->opacity() && !layer->OpacityIsAnimating() &&
          !layer->OpacityCanAnimateOnImplThread();
 }
@@ -1018,15 +1029,19 @@ static inline void RemoveSurfaceForEarlyExit(
 
 struct PreCalculateMetaInformationRecursiveData {
   bool layer_or_descendant_has_copy_request;
+  bool layer_or_descendant_has_event_handler;
   int num_unclipped_descendants;
 
   PreCalculateMetaInformationRecursiveData()
       : layer_or_descendant_has_copy_request(false),
+        layer_or_descendant_has_event_handler(false),
         num_unclipped_descendants(0) {}
 
   void Merge(const PreCalculateMetaInformationRecursiveData& data) {
     layer_or_descendant_has_copy_request |=
         data.layer_or_descendant_has_copy_request;
+    layer_or_descendant_has_event_handler |=
+        data.layer_or_descendant_has_event_handler;
     num_unclipped_descendants +=
         data.num_unclipped_descendants;
   }
@@ -1080,12 +1095,17 @@ static void PreCalculateMetaInformation(
   if (layer->HasCopyRequest())
     recursive_data->layer_or_descendant_has_copy_request = true;
 
+  if (LayerCanAcceptInput(layer))
+    recursive_data->layer_or_descendant_has_event_handler = true;
+
   layer->draw_properties().num_descendants_that_draw_content =
       num_descendants_that_draw_content;
   layer->draw_properties().num_unclipped_descendants =
       recursive_data->num_unclipped_descendants;
   layer->draw_properties().layer_or_descendant_has_copy_request =
       recursive_data->layer_or_descendant_has_copy_request;
+  layer->draw_properties().layer_or_descendant_has_event_handler =
+      recursive_data->layer_or_descendant_has_event_handler;
 }
 
 static void RoundTranslationComponents(gfx::Transform* transform) {
@@ -1142,6 +1162,7 @@ struct DataForRecursion {
   bool in_subtree_of_page_scale_application_layer;
   bool subtree_can_use_lcd_text;
   bool subtree_is_visible_from_ancestor;
+  bool subtree_has_event_handler;
 };
 
 template <typename LayerType>
@@ -1408,6 +1429,9 @@ static void CalculateDrawPropertiesInternal(
       data_from_ancestor.in_subtree_of_page_scale_application_layer;
   data_for_children.subtree_can_use_lcd_text =
       data_from_ancestor.subtree_can_use_lcd_text;
+  data_for_children.subtree_has_event_handler =
+      data_from_ancestor.subtree_has_event_handler ||
+      layer->draw_properties().layer_or_descendant_has_event_handler;
 
   // Layers with a copy request are always visible, as well as un-hiding their
   // subtree. Otherise, layers that are marked as hidden will hide themselves
@@ -1419,7 +1443,9 @@ static void CalculateDrawPropertiesInternal(
     layer_is_visible = true;
 
   // The root layer cannot skip CalcDrawProperties.
-  if (!IsRootLayer(layer) && SubtreeShouldBeSkipped(layer, layer_is_visible)) {
+  if (!IsRootLayer(layer) &&
+      !data_from_ancestor.subtree_has_event_handler &&
+      SubtreeShouldBeSkipped(layer, layer_is_visible)) {
     if (layer->render_surface())
       layer->ClearRenderSurface();
     return;
@@ -1847,7 +1873,8 @@ static void CalculateDrawPropertiesInternal(
   // and should be included in the sorting process.
   size_t sorting_start_index = descendants.size();
 
-  if (!LayerShouldBeSkipped(layer, layer_is_visible))
+  if (data_from_ancestor.subtree_has_event_handler ||
+      !LayerShouldBeSkipped(layer, layer_is_visible))
     descendants.push_back(layer);
 
   // Any layers that are appended after this point may need to be sorted if we
@@ -2145,6 +2172,9 @@ void LayerTreeHostCommon::CalculateDrawProperties(
 
   PreCalculateMetaInformationRecursiveData recursive_data;
   PreCalculateMetaInformation(inputs->root_layer, &recursive_data);
+  data_for_recursion.subtree_has_event_handler =
+      inputs->root_layer->draw_properties().
+          layer_or_descendant_has_event_handler;
   std::vector<AccumulatedSurfaceState<Layer> > accumulated_surface_state;
   CalculateDrawPropertiesInternal<Layer>(inputs->root_layer,
                                          globals,
@@ -2203,6 +2233,9 @@ void LayerTreeHostCommon::CalculateDrawProperties(
 
   PreCalculateMetaInformationRecursiveData recursive_data;
   PreCalculateMetaInformation(inputs->root_layer, &recursive_data);
+  data_for_recursion.subtree_has_event_handler =
+      inputs->root_layer->draw_properties().
+          layer_or_descendant_has_event_handler;
   std::vector<AccumulatedSurfaceState<LayerImpl> >
       accumulated_surface_state;
   CalculateDrawPropertiesInternal<LayerImpl>(inputs->root_layer,