Makes tile-creation lazy

cc/resources/picture_layer_tiling.h

Index: cc/resources/picture_layer_tiling.h
diff --git a/cc/resources/picture_layer_tiling.h b/cc/resources/picture_layer_tiling.h
index 7a71fa8c92768e19dc83e4896709d52717bddf68..ef6c3856e36e550fefb18e0e4f7462a7051fb286 100644
--- a/cc/resources/picture_layer_tiling.h
+++ b/cc/resources/picture_layer_tiling.h
@@ -26,11 +26,14 @@ class PictureLayerTilingClient {
   // tiling) This might return null if the client cannot create such a tile.
   virtual scoped_refptr<Tile> CreateTile(
     PictureLayerTiling* tiling,
-    gfx::Rect content_rect) = 0;
+    const gfx::Rect& content_rect,
+    const gfx::Rect& paint_rect) = 0;
   virtual void UpdatePile(Tile* tile) = 0;
   virtual gfx::Size CalculateTileSize(
     gfx::Size current_tile_size,
     gfx::Size content_bounds) = 0;
+  virtual const Region* GetInvalidation() = 0;
+  virtual const PictureLayerTiling* GetSibling(const PictureLayerTiling* tiling) = 0;
 };
 
 class CC_EXPORT PictureLayerTiling {
@@ -43,7 +46,6 @@ class CC_EXPORT PictureLayerTiling {
 
   gfx::Size layer_bounds() const { return layer_bounds_; }
   void SetLayerBounds(gfx::Size layer_bounds);
-  void Invalidate(const Region& layer_invalidation);
 
   // Add any tiles that intersect with |layer_rect|.  If any tiles already
   // exist, then this leaves them as-is.
@@ -146,22 +148,49 @@ class CC_EXPORT PictureLayerTiling {
   typedef base::hash_map<TileMapKey, scoped_refptr<Tile> > TileMap;
 
   PictureLayerTiling(float contents_scale);
+  PictureLayerTiling(const PictureLayerTiling& other, int);
   Tile* TileAt(int, int) const;
   void CreateTilesFromContentRect(gfx::Rect layer_rect);
   void CreateTile(int i, int j);
 
-  PictureLayerTilingClient* client_;
+  // Given properties.
   float contents_scale_;
   gfx::Size layer_bounds_;
-  gfx::Rect last_prioritized_rect_;
-  // It is not legal to have a NULL tile in the tiles_ map.
-  TileMap tiles_;
-  TilingData tiling_data_;
   TileResolution resolution_;
+  PictureLayerTilingClient* client_;
+
+  // Internal data.
+  TilingData tiling_data_;
+  TileMap tiles_;  // It is not legal to have a NULL tile in the tiles_ map.
+
+  // State saved for computing velocities based upon finite differences.
+  gfx::Rect interest_rect_;
+  gfx::Rect last_interest_rect_;
   int last_source_frame_number_;
   double last_impl_frame_time_;
 
-  friend class Iterator;
+  // An iterator that iterates over the TileMapKeys within a gfx::Rect.

[enne (OOO), 2013/03/27 16:16:27]

Do you need a new iterator class here? Why not just use TilingData::Iterator?

On a related note, I do agree with your offhand CL description suggestion that
PictureLayerTiling::Iterator and PictureLayerTilingSet::Iterator should probably
be named CoverageIterator.  I'll put up a quick patch to do that.

+  class CC_EXPORT SimpleIterator {
+   public:
+    SimpleIterator(const PictureLayerTiling* tiling,
+                   const gfx::Rect& rect);  // we assume rect is contained

[enne (OOO), 2013/03/27 16:16:27]

Please don't make multi-line comments at the end of a line of code.  They're
really awkward to reformat.

+                                            // within tiling's content
+
+    TileMapKey operator->() const { return key_; }
+    TileMapKey operator*() const { return key_; }
+
+    SimpleIterator& operator++();
+    operator bool() const { return key_.second < bottom_; }
+
+   private:
+    TileMapKey key_;
+    int left_;
+    int right_;  // left_ <= key_.first < right_
+    int bottom_;  // key_.second < bottom_
+  };
+
+  void ManageTiles(const gfx::Rect& old_interest_rect,
+                   const gfx::Rect& new_interest_rect);
 };
 
 }  // namespace cc