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 d483cc697bd76d44e0b7d9353dbb0974c6fdfc5d..b496ee5da9c1a65049bd8d9bb0807bd07de57cdc 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) {
+  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,
@@ -415,7 +421,16 @@ static inline bool TransformToScreenIsKnown(Layer* layer) {
 
 template <typename LayerType>
 static bool LayerShouldBeSkipped(LayerType* layer,
-                                 bool layer_is_visible) {
+                                 bool layer_is_visible,
+                                 bool visit_for_event_handler_only) {

[danakj, 2013/10/08 18:32:32]

how about bool "layer_has_zero_opacity"? only is a bit of a loaded term here,
you might be here for event handlers and also for copy requests.

+  // If an ancestor node was going to be skipped, but wasn't only because it had
+  // event handlers in the subtree, and there are not event handlers in the
+  // subtree rooted at |layer|, then skip this layer.
+  if (visit_for_event_handler_only &&

[danakj, 2013/10/08 18:32:32]

Move this down below the big intro comment, and update the intro comment to
accomodate this.

+      !layer->draw_properties().layer_or_descendant_has_event_handler) {
+    return true;
+  }
+
   // Layers can be skipped if any of these conditions are met.
   //   - is not visible due to it or one of its ancestors being hidden.
   //   - has empty bounds
@@ -452,18 +467,27 @@ 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)
+  // A layer cannot be skipped if it is subject to hit-testing.
+  if (LayerCanAcceptInput(layer))
+    return false;
+
+  if (!layer->DrawsContent())
+    return true;
+
+  if (!layer->draw_opacity() && !layer->draw_opacity_is_animating())

[danakj, 2013/10/08 18:32:32]

Animating only matters on the main thread. On the impl thread we should ignore
it. This needs to be covered by a test.

If the layer owns a surface, it'll have draw opacity of 1 and I believe that
visit_for_event_handler_only will be false. But it should be skipped since its
surface has opacity 0. This needs to be covered by a test.

     return true;
 
   return false;
 }
 
 static inline bool SubtreeShouldBeSkipped(LayerImpl* layer,
-                                          bool layer_is_visible) {
+                                          bool layer_is_visible,
+                                          bool *visit_for_event_handler_only) {
+  if (*visit_for_event_handler_only &&
+      !layer->draw_properties().layer_or_descendant_has_event_handler) {
+    return true;
+  }
+
   // When we need to do a readback/copy of a layer's output, we can not skip
   // it or any of its ancestors.
   if (layer->draw_properties().layer_or_descendant_has_copy_request)
@@ -479,15 +503,30 @@ static inline bool SubtreeShouldBeSkipped(LayerImpl* layer,
   if (layer->layer_tree_impl()->IsPendingTree() && layer->OpacityIsAnimating())
     return false;
 
+  bool skip_if_no_event_handler = !layer->opacity();
+
+  // If the layer (or any of its descendant) is subject to hit-testing, then the
+  // subtree cannot be skipped.
+  if (layer->draw_properties().layer_or_descendant_has_event_handler) {
+    if (skip_if_no_event_handler)
+      *visit_for_event_handler_only = true;
+    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();
+  return skip_if_no_event_handler;
 }
 
 static inline bool SubtreeShouldBeSkipped(Layer* layer,
-                                          bool layer_is_visible) {
+                                          bool layer_is_visible,
+                                          bool* visit_for_event_handler_only) {
+  if (*visit_for_event_handler_only &&
+      !layer->draw_properties().layer_or_descendant_has_event_handler) {
+    return true;
+  }
+
   // When we need to do a readback/copy of a layer's output, we can not skip
   // it or any of its ancestors.
   if (layer->draw_properties().layer_or_descendant_has_copy_request)
@@ -503,9 +542,19 @@ static inline bool SubtreeShouldBeSkipped(Layer* layer,
   // 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();
+  bool skip_if_no_event_handler =
+      !layer->opacity() && !layer->OpacityIsAnimating() &&
+      !layer->OpacityCanAnimateOnImplThread();
+
+  // If the layer (or any of its descendant) is subject to hit-testing, then the
+  // subtree cannot be skipped.
+  if (layer->draw_properties().layer_or_descendant_has_event_handler) {
+    if (skip_if_no_event_handler)
+      *visit_for_event_handler_only = true;
+    return false;
+  }
+
+  return skip_if_no_event_handler;
 }
 
 // Called on each layer that could be drawn after all information from
@@ -1014,15 +1063,19 @@ 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;
   }
@@ -1084,6 +1137,9 @@ 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 =
@@ -1092,6 +1148,8 @@ static void PreCalculateMetaInformation(
       descendants_can_clip_selves;
   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) {
@@ -1147,6 +1205,8 @@ struct DataForRecursion {
   bool in_subtree_of_page_scale_application_layer;
   bool subtree_can_use_lcd_text;
   bool subtree_is_visible_from_ancestor;
+
+  bool visit_for_event_handler_only;
 };
 
 // Recursively walks the layer tree starting at the given node and computes all
@@ -1306,12 +1366,17 @@ static void CalculateDrawPropertiesInternal(
   if (layer->HasCopyRequest())
     layer_is_visible = true;
 
+  bool visit_for_event_handler_only =
+      data_from_ancestor.visit_for_event_handler_only;
   // The root layer cannot skip CalcDrawProperties.
-  if (!IsRootLayer(layer) && SubtreeShouldBeSkipped(layer, layer_is_visible)) {
+  if (!IsRootLayer(layer) &&
+      SubtreeShouldBeSkipped(layer, layer_is_visible,
+                             &visit_for_event_handler_only)) {
     if (layer->render_surface())
       layer->ClearRenderSurface();
     return;
   }
+  data_for_children.visit_for_event_handler_only = visit_for_event_handler_only;
 
   // We need to circumvent the normal recursive flow of information for clip
   // children (they don't inherit their direct ancestor's clip information).
@@ -1729,7 +1794,8 @@ 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 (!LayerShouldBeSkipped(layer, layer_is_visible,
+                            data_from_ancestor.visit_for_event_handler_only))
     descendants.push_back(layer);
 
   if (!layer->children().empty()) {
@@ -1826,7 +1892,8 @@ static void CalculateDrawPropertiesInternal(
   }
 
   // Compute the layer's visible content rect (the rect is in content space).
-  layer_draw_properties.visible_content_rect = CalculateVisibleContentRect(
+  layer_draw_properties.visible_content_rect =

[danakj, 2013/10/08 18:32:32]

Leave this rect alone. If the layer has 0 opacity but is going to animate to be
visible, we'd like to not destroy our chances of knowing what to raster.

+      visit_for_event_handler_only ? gfx::Rect() : CalculateVisibleContentRect(
       layer, clip_rect_of_target_surface_in_target_space, rect_in_target_space);
 
   // Compute the remaining properties for the render surface, if the layer has
@@ -1982,6 +2049,7 @@ void LayerTreeHostCommon::CalculateDrawProperties(
   data_for_recursion.in_subtree_of_page_scale_application_layer = false;
   data_for_recursion.subtree_can_use_lcd_text = inputs->can_use_lcd_text;
   data_for_recursion.subtree_is_visible_from_ancestor = true;
+  data_for_recursion.visit_for_event_handler_only = false;
 
   PreCalculateMetaInformationRecursiveData recursive_data;
   PreCalculateMetaInformation(inputs->root_layer, &recursive_data);
@@ -2041,6 +2109,7 @@ void LayerTreeHostCommon::CalculateDrawProperties(
   data_for_recursion.in_subtree_of_page_scale_application_layer = false;
   data_for_recursion.subtree_can_use_lcd_text = inputs->can_use_lcd_text;
   data_for_recursion.subtree_is_visible_from_ancestor = true;
+  data_for_recursion.visit_for_event_handler_only = false;
 
   PreCalculateMetaInformationRecursiveData recursive_data;
   PreCalculateMetaInformation(inputs->root_layer, &recursive_data);