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

cc/trees/layer_tree_host_common.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_common.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "cc/base/math_util.h"
@@ skipping 45 matching lines @@
 static gfx::Vector2dF GetEffectiveTotalScrollOffset(LayerType* layer) {
   gfx::Vector2dF offset = layer->TotalScrollOffset();
   // The scroll parent's total scroll offset (scroll offset + scroll delta)
   // can't be used because its scroll offset has already been applied to the
   // scroll children's positions by the main thread layer positioning code.
   if (layer->scroll_parent())
     offset += layer->scroll_parent()->ScrollDelta();
   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,
     gfx::Rect layer_rect_in_target_space,
     const gfx::Transform& transform) {
   if (layer_rect_in_target_space.IsEmpty())
     return gfx::Rect();
 
   // Is this layer fully contained within the target surface?
   if (target_surface_rect.Contains(layer_rect_in_target_space))
@@ skipping 369 matching lines @@
     backface_test_layer = layer->parent();
   }
 
   // The layer should not be drawn if (1) it is not double-sided and (2) the
   // back of the layer is known to be facing the screen.
   if (!backface_test_layer->double_sided() &&
       TransformToScreenIsKnown(backface_test_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;
 
-  return false;
+  return !layer->draw_opacity() && !layer->draw_opacity_is_animating();

[enne (OOO), 2013/10/07 17:27:23]

I'm not sure this is adequate.

If you have:
-A
  -B
  -C

...and C accepts input and A has zero opacity, then B will now appear in the
RSLL where it didn't before.  If B is a PictureLayerImpl then it'll go ahead and
create resources wastefully.

Does there need to be some "in skipped subtree" boolean that gets passed to
children and considered in LayerShouldBeSkipped? 

[danakj, 2013/10/07 17:37:35]

Can you make this a if () return true; and keep return false at the end of the
method?

[danakj, 2013/10/07 17:37:35]

PictureLayerImpl should probably consider its draw opacity the same way it
considers DrawsContent?

[enne (OOO), 2013/10/07 17:45:51]

It's more than that.  What if you've set a subtree to not be visible and some
descendant has a copy request?

I'm suggesting that maybe this could be generalized to a "this subtree could not
be skipped because of some descendant" property and then every layer in such a
tree is individually skipped except for those specific descendants.

[sadrul, 2013/10/07 18:37:24]

Done.

[sadrul, 2013/10/07 18:37:24]

I am going through the code to completely grok this suggestion.

 }
 
 static inline bool SubtreeShouldBeSkipped(LayerImpl* layer,
                                           bool layer_is_visible) {
   // 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)
     return false;
 
   // If the layer is not visible, then skip it and its subtree.
   if (!layer_is_visible)
     return true;
 
   // If layer is on the pending tree and opacity is being animated then
   // this subtree can't be skipped as we need to create, prioritize and
   // include tiles for this layer when deciding if tree can be activated.
   if (layer->layer_tree_impl()->IsPendingTree() && layer->OpacityIsAnimating())
     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();
+  // entire subtree can be skipped if this layer is fully transparent, and none
+  // of layers in the subtree has event handlers.
+  return !layer->opacity() &&
+         !layer->draw_properties().layer_or_descendant_has_event_handler;
 }
 
 static inline bool SubtreeShouldBeSkipped(Layer* layer,
                                           bool layer_is_visible) {
   // 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)
     return false;
 
   // If the layer is not visible, then skip it and its subtree.
   if (!layer_is_visible)
     return true;
 
   // 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();
+         !layer->OpacityCanAnimateOnImplThread() &&
+         !layer->draw_properties().layer_or_descendant_has_event_handler;

[enne (OOO), 2013/10/07 17:27:23]

Can you break out this condition from the rest of the opacity ones, since it's
not related to opacity? Same thing for the other function above?

[sadrul, 2013/10/07 18:37:24]

Done.

 }
 
 // Called on each layer that could be drawn after all information from
 // CalcDrawProperties has been updated on that layer.  May have some false
 // positives (e.g. layers get this called on them but don't actually get drawn).
 static inline void UpdateTilePrioritiesForLayer(LayerImpl* layer) {
   layer->UpdateTilePriorities();
 
   // Mask layers don't get this call, so explicitly update them so they can
   // kick off tile rasterization.
@@ skipping 488 matching lines @@
     render_surface_layer_list->back()->ClearRenderSurface();
     render_surface_layer_list->pop_back();
   }
   DCHECK_EQ(render_surface_layer_list->back(), layer_to_remove);
   render_surface_layer_list->pop_back();
   layer_to_remove->ClearRenderSurface();
 }
 
 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;
   }
 };
 
 // Recursively walks the layer tree to compute any information that is needed
 // before doing the main recursion.
 template <typename LayerType>
 static void PreCalculateMetaInformation(
     LayerType* layer,
@@ skipping 41 matching lines @@
 
   if (layer->clip_children()) {
     int num_clip_children = layer->clip_children()->size();
     DCHECK_GE(recursive_data->num_unclipped_descendants, num_clip_children);
     recursive_data->num_unclipped_descendants -= num_clip_children;
   }
 
   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().descendants_can_clip_selves =
       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) {
   transform->matrix().set(0, 3, MathUtil::Round(transform->matrix().get(0, 3)));
   transform->matrix().set(1, 3, MathUtil::Round(transform->matrix().get(1, 3)));
 }
 
 template <typename LayerType>
 struct SubtreeGlobals {
   LayerSorter* layer_sorter;
@@ skipping 1141 matching lines @@
   // At this point, we think the point does hit the touch event handler region
   // on the layer, but we need to walk up the parents to ensure that the layer
   // was not clipped in such a way that the hit point actually should not hit
   // the layer.
   if (PointIsClippedBySurfaceOrClipRect(screen_space_point, layer_impl))
     return false;
 
   return true;
 }
 }  // namespace cc