cc : Seperate adding clip node and setting render surface is_clipped

cc/trees/property_tree_builder.cc

 // Copyright 2014 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/property_tree_builder.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <set>
@@ skipping 35 matching lines @@
   const LayerType* inner_viewport_scroll_layer;
   const LayerType* outer_viewport_scroll_layer;
   const LayerType* overscroll_elasticity_layer;
   gfx::Vector2dF elastic_overscroll;
   float page_scale_factor;
   bool in_subtree_of_page_scale_layer;
   bool affected_by_inner_viewport_bounds_delta;
   bool affected_by_outer_viewport_bounds_delta;
   bool should_flatten;
   bool is_hidden;
+  bool apply_ancestor_clip;
   uint32_t main_thread_scrolling_reasons;
   bool scroll_tree_parent_created_by_uninheritable_criteria;
   const gfx::Transform* device_transform;
   gfx::Transform compound_transform_since_render_target;
   bool axis_align_since_render_target;
   SkColor safe_opaque_background_color;
 };
 
 template <typename LayerType>
 struct DataForRecursionFromChild {
@@ skipping 265 matching lines @@
 
 static Layer* Parent(Layer* layer) {
   return layer->parent();
 }
 
 static LayerImpl* Parent(LayerImpl* layer) {
   return layer->test_properties()->parent;
 }
 
 template <typename LayerType>
+static void SetSurfaceIsClipped(DataForRecursion<LayerType>* data_for_children,
+                                bool apply_ancestor_clip,
+                                LayerType* layer) {
+  // A surface with unclipped descendants cannot be clipped by its ancestor
+  // clip at draw time since the unclipped descendants aren't affected by the
+  // ancestor clip.
+  EffectNode* effect_node = data_for_children->property_trees->effect_tree.Node(
+      data_for_children->render_target);
+  DCHECK_EQ(effect_node->owner_id, layer->id());
+  effect_node->surface_is_clipped =
+      apply_ancestor_clip && !NumUnclippedDescendants(layer);
+  // The ancestor clip should propagate to children only if the surface doesn't
+  // apply the clip.
+  data_for_children->apply_ancestor_clip =
+      apply_ancestor_clip && !effect_node->surface_is_clipped;
+}
+
+template <typename LayerType>
 void AddClipNodeIfNeeded(const DataForRecursion<LayerType>& data_from_ancestor,
                          LayerType* layer,
                          bool created_render_surface,
                          bool created_transform_node,
                          DataForRecursion<LayerType>* data_for_children) {
   ClipNode* parent = GetClipParent(data_from_ancestor, layer);

[weiliangc, 2016/12/01 20:09:26]

Since GetClipParent() also has two code path depends on ClipParent(), maybe
remove this helper function and merge with apply_ancestor_clip calculation?

[jaydasika, 2016/12/02 05:20:56]

Done.

   int parent_id = parent->id;
 
-  bool is_root = !Parent(layer);
+  bool inherits_clip = !ClipParent(layer);
 
-  // Whether we have an ancestor clip that we might need to apply.
-  bool ancestor_clips_subtree = is_root || parent->layers_are_clipped;
+  bool apply_ancestor_clip = inherits_clip
+                                 ? data_from_ancestor.apply_ancestor_clip
+                                 : parent->layers_are_clipped;

[jaydasika, 2016/12/01 09:12:54]

apply_ancestor_clip here still depends on having a clip node for render surfaces
as it uses parent->layers_are_clipped. But, in the code where we do not create
clip nodes for render surfaces, it will not depend on it.

[weiliangc, 2016/12/01 20:09:26]

Could you clarify when apply_ancestor_clip would be different from old
ancestor_clips_subtree?

[jaydasika, 2016/12/02 05:20:56]

Its the same. Its just computed differently now.
This is required because when we stop creating clip nodes for render surfaces,
there won't be layers_are_clipped anymore (as it will always be true) and so we
have to track whether to apply ancestor clip using a recursion variable (which
this CL does).
When we have clip parent we still use parent's layers_are_clipped value here,
but it won't be the case in the new code path. 

 
   bool layers_are_clipped = false;
   bool has_unclipped_surface = false;
 
   if (created_render_surface) {
+    SetSurfaceIsClipped(data_for_children, apply_ancestor_clip, layer);
     // Clips can usually be applied to a surface's descendants simply by
     // clipping the surface (or applied implicitly by the surface's bounds).
     // However, if the surface has unclipped descendants (layers that aren't
     // affected by the ancestor clip), we cannot clip the surface itself, and
     // must instead apply clips to the clipped descendants.
-    if (ancestor_clips_subtree && NumUnclippedDescendants(layer) > 0) {
+    if (apply_ancestor_clip && NumUnclippedDescendants(layer) > 0) {
       layers_are_clipped = true;
-    } else if (!ancestor_clips_subtree) {
+    } else if (!apply_ancestor_clip) {
       // When there are no ancestor clips that need to be applied to a render
       // surface, we reset clipping state. The surface might contribute a clip
       // of its own, but clips from ancestor nodes don't need to be considered
       // when computing clip rects or visibility.
       has_unclipped_surface = true;
       DCHECK_NE(parent->clip_type, ClipNode::ClipType::APPLIES_LOCAL_CLIP);
     }
-    // A surface with unclipped descendants cannot be clipped by its ancestor
-    // clip at draw time since the unclipped descendants aren't affected by the
-    // ancestor clip.
-    EffectNode* effect_node =
-        data_for_children->property_trees->effect_tree.Node(
-            data_for_children->render_target);
-    DCHECK(effect_node->owner_id == layer->id());
-    effect_node->surface_is_clipped =
-        ancestor_clips_subtree && !NumUnclippedDescendants(layer);
   } else {
     // Without a new render surface, layer clipping state from ancestors needs
     // to continue to propagate.
-    layers_are_clipped = ancestor_clips_subtree;
+    layers_are_clipped = apply_ancestor_clip;
   }
 
   bool layer_clips_subtree = LayerClipsSubtree(layer);
-  if (layer_clips_subtree)
+  if (layer_clips_subtree) {
     layers_are_clipped = true;
+    data_for_children->apply_ancestor_clip = true;
+  }
 
   // Without surfaces, all non-viewport clips have to be applied using layer
   // clipping.
   bool layers_are_clipped_when_surfaces_disabled =
       layer_clips_subtree || parent->layers_are_clipped_when_surfaces_disabled;
 
   // Render surface's clip is needed during hit testing. So, we need to create
   // a clip node for every render surface.
   bool requires_node = layer_clips_subtree || created_render_surface;
 
@@ skipping 11 matching lines @@
     ClipNode node;
     node.clip = gfx::RectF(gfx::PointF() + layer->offset_to_transform_parent(),
                            gfx::SizeF(layer->bounds()));
     node.transform_id = transform_parent->transform_tree_index();
     node.target_effect_id = data_for_children->render_target;
     node.target_transform_id = data_for_children->property_trees->effect_tree
                                    .Node(data_for_children->render_target)
                                    ->transform_id;
     node.owner_id = layer->id();
 
-    if (ancestor_clips_subtree || layer_clips_subtree) {
+    if (apply_ancestor_clip || layer_clips_subtree) {
       // Surfaces reset the rect used for layer clipping. At other nodes, layer
       // clipping state from ancestors must continue to get propagated.
       node.layer_clipping_uses_only_local_clip =
           (created_render_surface && NumUnclippedDescendants(layer) == 0) ||
-          !ancestor_clips_subtree;
+          !apply_ancestor_clip;
     } else {
       // Otherwise, we're either unclipped, or exist only in order to apply our
       // parent's clips in our space.
       node.layer_clipping_uses_only_local_clip = false;
     }
 
     if (layer_clips_subtree)
       node.clip_type = ClipNode::ClipType::APPLIES_LOCAL_CLIP;
     else
       node.clip_type = ClipNode::ClipType::NONE;
@@ skipping 946 matching lines @@
   data_for_recursion.inner_viewport_scroll_layer = inner_viewport_scroll_layer;
   data_for_recursion.outer_viewport_scroll_layer = outer_viewport_scroll_layer;
   data_for_recursion.overscroll_elasticity_layer = overscroll_elasticity_layer;
   data_for_recursion.elastic_overscroll = elastic_overscroll;
   data_for_recursion.page_scale_factor = page_scale_factor;
   data_for_recursion.in_subtree_of_page_scale_layer = false;
   data_for_recursion.affected_by_inner_viewport_bounds_delta = false;
   data_for_recursion.affected_by_outer_viewport_bounds_delta = false;
   data_for_recursion.should_flatten = false;
   data_for_recursion.is_hidden = false;
+  // The root clip is always applied.
+  data_for_recursion.apply_ancestor_clip = true;
   data_for_recursion.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
   data_for_recursion.scroll_tree_parent_created_by_uninheritable_criteria =
       true;
   data_for_recursion.device_transform = &device_transform;
 
   data_for_recursion.property_trees->clear();
   data_for_recursion.compound_transform_since_render_target = gfx::Transform();
   data_for_recursion.axis_align_since_render_target = true;
   data_for_recursion.property_trees->transform_tree.set_device_scale_factor(
@@ skipping 92 matching lines @@
     color = SkColorSetA(color, 255);
   BuildPropertyTreesTopLevelInternal(
       root_layer, page_scale_layer, inner_viewport_scroll_layer,
       outer_viewport_scroll_layer, overscroll_elasticity_layer,
       elastic_overscroll, page_scale_factor, device_scale_factor, viewport,
       device_transform, property_trees, color);
   property_trees->ResetCachedData();
 }
 
 }  // namespace cc