cc : Snap texture layers to pixel boundary

cc/trees/transform_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_TRANSFORM_NODE_H_
 #define CC_TREES_TRANSFORM_NODE_H_
 
 #include "cc/base/cc_export.h"
 #include "ui/gfx/geometry/point_f.h"
 #include "ui/gfx/geometry/scroll_offset.h"
@@ skipping 76 matching lines @@
 
   // This is true if the to_parent transform at every node on the path to the
   // root is flat.
   bool node_and_ancestors_are_flat : 1;
 
   // This is needed to know if a layer can use lcd text.
   bool node_and_ancestors_have_only_integer_translation : 1;
 
   bool scrolls : 1;
 
+  bool should_be_snapped : 1;
+
   bool needs_surface_contents_scale : 1;
 
   // These are used to position nodes wrt the right or bottom of the inner or
   // outer viewport.
   bool affected_by_inner_viewport_bounds_delta_x : 1;
   bool affected_by_inner_viewport_bounds_delta_y : 1;
   bool affected_by_outer_viewport_bounds_delta_x : 1;
   bool affected_by_outer_viewport_bounds_delta_y : 1;
 
   // Layer scale factor is used as a fallback when we either cannot adjust
   // raster scale or if the raster scale cannot be extracted from the screen
   // space transform. For layers in the subtree of the page scale layer, the
   // layer scale factor should include the page scale factor.
   bool in_subtree_of_page_scale_layer : 1;
 
   // We need to track changes to to_screen transform to compute the damage rect.
   bool transform_changed : 1;
 
   // TODO(vollick): will be moved when accelerated effects are implemented.
   float post_local_scale_factor;
 
   gfx::Vector2dF surface_contents_scale;
 
   // TODO(vollick): will be moved when accelerated effects are implemented.
   gfx::ScrollOffset scroll_offset;
 
-  // We scroll snap where possible, but this means fixed-pos elements must be
-  // adjusted.  This value stores the snapped amount for this purpose.
-  gfx::Vector2dF scroll_snap;
+  // This value stores the snapped amount whenever we snap. If the snap is due
+  // to a scroll, we need it to calculate fixed-pos elements adjustment, even
+  // otherwise we may need it to undo the snapping next frame.
+  gfx::Vector2dF snap_amount;
 
   // TODO(vollick): will be moved when accelerated effects are implemented.
   gfx::Vector2dF source_offset;
   gfx::Vector2dF source_to_parent;
 
   bool operator==(const TransformNode& other) const;
 
   void set_to_parent(const gfx::Transform& transform) {
     to_parent = transform;
     is_invertible = to_parent.IsInvertible();
@@ skipping 27 matching lines @@
 
   bool operator==(const TransformCachedNodeData& other) const;
 
   void ToProtobuf(proto::TransformCachedNodeData* proto) const;
   void FromProtobuf(const proto::TransformCachedNodeData& proto);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_TRANSFORM_NODE_H_