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) {

[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,
     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 354 matching lines @@
 
 static inline bool TransformToScreenIsKnown(Layer* layer) {
   return !layer->screen_space_transform_is_animating();
 }
 
 template <typename LayerType>
 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.
   //   - the intersection of render_surface content and layer clip_rect is empty
   //   - the visible_content_rect is empty
   //
   // Note, if the layer should not have been drawn due to being fully
   // transparent, we would have skipped the entire subtree and never made it
   // into this function, so it is safe to omit this check here.
 
   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;
 
   LayerType* backface_test_layer = layer;
   if (layer->use_parent_backface_visibility()) {
     DCHECK(layer->parent());
     DCHECK(!layer->parent()->use_parent_backface_visibility());
     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)
+  // The layer is visible to events.
+  if (!layer->DrawsContent())
     return true;
 
   return false;
 }
 
 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;
 
+  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();
 }
 
 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 (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();
 }
 
 static inline void SavePaintPropertiesLayer(LayerImpl* layer) {}
 
 static inline void SavePaintPropertiesLayer(Layer* layer) {
   layer->SavePaintProperties();
 
   if (layer->mask_layer())
@@ skipping 475 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 33 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().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 36 matching lines @@
   // while dealing with the parent layer, and then this precomputed value is
   // passed down the recursion to the children that actually use it.
   gfx::Rect clip_rect_of_target_surface_in_target_space;
 
   bool ancestor_clips_subtree;
   typename LayerType::RenderSurfaceType*
       nearest_ancestor_surface_that_moves_pixels;
   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>
 static LayerType* GetChildContainingLayer(const LayerType& parent,
                                           LayerType* layer) {
   for (LayerType* ancestor = layer; ancestor; ancestor = ancestor->parent()) {
     if (ancestor->parent() == &parent)
       return ancestor;
   }
   NOTREACHED();
@@ skipping 246 matching lines @@
          (globals.page_scale_factor == 1.f));
 
   DataForRecursion<LayerType> data_for_children;
   typename LayerType::RenderSurfaceType*
       nearest_ancestor_surface_that_moves_pixels =
           data_from_ancestor.nearest_ancestor_surface_that_moves_pixels;
   data_for_children.in_subtree_of_page_scale_application_layer =
       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
   // and their subtree.
   bool layer_is_visible =
       data_from_ancestor.subtree_is_visible_from_ancestor &&
       !layer->hide_layer_and_subtree();
   if (layer->HasCopyRequest())
     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;
   }
 
   // We need to circumvent the normal recursive flow of information for clip
   // children (they don't inherit their direct ancestor's clip information).
   // This is unfortunate, and would be unnecessary if we were to formally
   // separate the clipping hierarchy from the layer hierarchy.
   bool ancestor_clips_subtree = data_from_ancestor.ancestor_clips_subtree;
@@ skipping 407 matching lines @@
   }
 
   typename LayerType::RenderSurfaceListType& descendants =
       (layer->render_surface() ? layer->render_surface()->layer_list()
                                : *layer_list);
 
   // Any layers that are appended after this point are in the layer's subtree
   // 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
   // visit the children out of order.
   size_t render_surface_layer_list_child_sorting_start_index =
       render_surface_layer_list->size();
   size_t layer_list_child_sorting_start_index = descendants.size();
 
   if (!layer->children().empty()) {
     if (layer == globals.page_scale_application_layer) {
@@ skipping 277 matching lines @@
   data_for_recursion.clip_rect_of_target_surface_in_target_space =
       device_viewport_rect;
   data_for_recursion.ancestor_clips_subtree = true;
   data_for_recursion.nearest_ancestor_surface_that_moves_pixels = NULL;
   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;
 
   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,
                                          data_for_recursion,
                                          inputs->render_surface_layer_list,
                                          &dummy_layer_list,
                                          &accumulated_surface_state);
 
   // The dummy layer list should not have been used.
   DCHECK_EQ(0u, dummy_layer_list.size());
@@ skipping 38 matching lines @@
   data_for_recursion.clip_rect_of_target_surface_in_target_space =
       device_viewport_rect;
   data_for_recursion.ancestor_clips_subtree = true;
   data_for_recursion.nearest_ancestor_surface_that_moves_pixels = NULL;
   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;
 
   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,
                                              globals,
                                              data_for_recursion,
                                              inputs->render_surface_layer_list,
                                              &dummy_layer_list,
                                              &accumulated_surface_state);
 
   // The dummy layer list should not have been used.
@@ skipping 175 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