cc : Clean up cc clip tree

cc/trees/clip_node.h

 // Copyright 2016 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.
 
 #ifndef CC_TREES_CLIP_NODE_H_
 #define CC_TREES_CLIP_NODE_H_
 
 #include <memory>
 
 #include "cc/base/cc_export.h"
@@ skipping 17 matching lines @@
   ~ClipNode();
 
   // The node index of this node in the clip tree node vector.
   int id;
   // The node index of the parent node in the clip tree node vector.
   int parent_id;
   // The layer id of the layer that owns this node.
   int owning_layer_id;
 
   enum class ClipType {
-    // The node doesn't contribute a new clip. It exists only for caching clips
-    // or for resetting clipping state.
-    NONE,
-
     // The node contributes a new clip (that is, |clip| needs to be applied).
     APPLIES_LOCAL_CLIP,
 
     // This node represents a space expansion. When computing visible rects,
     // the accumulated clip inherited by this node gets expanded. Similarly,
     // when mapping a rect in descendant space to the rect in ancestor space
     // that depends on the descendant rect's contents, this node expands the
     // descendant rect. This is used for effects like pixel-moving filters,
     // where clipped-out content can affect visible output.
     EXPANDS_CLIP
   };
 
   ClipType clip_type;
 
   // The clip rect that this node contributes, expressed in the space of its
   // transform node.
   gfx::RectF clip;
 
+  // Each element of this cache stores the accumulated clip from this clip
+  // node to a particular target.
+  mutable std::vector<ClipRectData> cached_clip_rects;
+
+  // This rect accumulates all clips from this node to the root in screen space.
+  // It is used in the computation of layer's visible rect.
+  gfx::RectF accumulated_rect_in_screen_space;

[weiliangc, 2017/03/14 22:04:29]

Is this also a cached value? Could this be expressed as cached_clip_rects where
the target is screen?

[jaydasika, 2017/03/16 20:33:30]

Yes, it is a cached value and it can be expressed in cached_clip_rects with
is_clipped = true and target_id = root_id, but I found that its faster to fetch
this when its stored separately (because we won't have to iterate through the
vector).

+
   // For nodes that expand, this represents the amount of expansion.
   std::unique_ptr<ClipExpander> clip_expander;
 
-  // Clip nodes are used for two reasons. First, they are used for determining
-  // which parts of each layer are visible. Second, they are used for
-  // determining whether a clip needs to be applied when drawing a layer, and if
-  // so, the rect that needs to be used. These can be different since not all
-  // clips need to be applied directly to each layer. For example, a layer is
-  // implicitly clipped by the bounds of its target render surface and by clips
-  // applied to this surface. |combined_clip_in_target_space| is used for
-  // computing visible rects, and |clip_in_target_space| is used for computing
-  // clips applied at draw time. Both rects are expressed in the space of the
-  // target transform node, and may include clips contributed by ancestors.
-  gfx::RectF combined_clip_in_target_space;
-  gfx::RectF clip_in_target_space;
-
   // The id of the transform node that defines the clip node's local space.
   int transform_id;
 
-  // The id of the transform node that defines the clip node's target space.
-  int target_transform_id;
-
-  // The id of the effect node that defines the clip node's target space.
-  // TODO(crbug.com/642581 crbug.com/642584): As we progress toward SPv2 and
-  // layer list mode, there may be layers having the same clip but draw onto
-  // different target. Target information shall be removed from here.
-  int target_effect_id;
-
-  // When true, |clip_in_target_space| does not include clips from ancestor
-  // nodes.
-  bool layer_clipping_uses_only_local_clip : 1;
-
-  // True if layers with this clip tree node need to be drawn with a clip
-  // applied.
-  bool layers_are_clipped : 1;
-  bool layers_are_clipped_when_surfaces_disabled : 1;
-
-  // Nodes that correspond to unclipped surfaces disregard ancestor clips.
-  bool resets_clip : 1;
-
   bool operator==(const ClipNode& other) const;
 
   void AsValueInto(base::trace_event::TracedValue* value) const;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_CLIP_NODE_H_