cc: Add ReverseSpiralDifferenceIterator.

cc/base/tiling_data.h

Index: cc/base/tiling_data.h
diff --git a/cc/base/tiling_data.h b/cc/base/tiling_data.h
index a2e0a136967df3b4b2c77834adbfee08a2affdfa..08d421c47fe270c85a72602cf4ad156a9ac2bb3d 100644
--- a/cc/base/tiling_data.h
+++ b/cc/base/tiling_data.h
@@ -182,6 +182,66 @@ class CC_EXPORT TilingData {
     int vertical_step_count_;
   };
 
+  class CC_EXPORT ReverseSpiralDifferenceIterator : public BaseIterator {
+   public:
+    ReverseSpiralDifferenceIterator();
+    ReverseSpiralDifferenceIterator(const TilingData* tiling_data,
+                                    const gfx::Rect& consider_rect,
+                                    const gfx::Rect& ignore_rect,
+                                    const gfx::Rect& center_rect);
+    ReverseSpiralDifferenceIterator& operator++();
+
+   private:
+    bool in_consider_rect() const {
+      return index_x_ >= consider_left_ && index_x_ <= consider_right_ &&
+             index_y_ >= consider_top_ && index_y_ <= consider_bottom_;
+    }
+    bool in_around_rect() const {
+      return index_x_ >= around_left_ && index_x_ <= around_right_ &&
+             index_y_ >= around_top_ && index_y_ <= around_bottom_;
+    }
+    bool in_ignore_rect() const {
+      return index_x_ >= ignore_left_ && index_x_ <= ignore_right_ &&
+             index_y_ >= ignore_top_ && index_y_ <= ignore_bottom_;
+    }
+    bool valid_column() const {
+      return index_x_ >= consider_left_ && index_x_ <= consider_right_;
+    }
+    bool valid_row() const {
+      return index_y_ >= consider_top_ && index_y_ <= consider_bottom_;
+    }
+
+    int current_step_count() const {
+      return (direction_ == UP || direction_ == DOWN) ? vertical_step_count_
+                                                      : horizontal_step_count_;
+    }
+
+    bool needs_direction_switch() const;
+    void switch_direction();
+
+    int consider_left_;
+    int consider_top_;
+    int consider_right_;
+    int consider_bottom_;
+    int around_left_;
+    int around_top_;
+    int around_right_;
+    int around_bottom_;

[ajuma, 2014/10/15 17:56:52]

Just to make sure I'm understanding, the reason we need to store the around rect
for this iterator but not for the SpiralDifferenceIterator is that it determines
the end state of this iterator but just the start state of the
SpiralDifferenceIterator?

[vmpstr, 2014/10/15 18:10:46]

That's correct. In the outward spiral, we just start with around and set the
step counts in such a way that we don't ever enter the around rect. Here, we
kinda have to end up in the around rect, so hence storing the values.

+    int ignore_left_;
+    int ignore_top_;
+    int ignore_right_;
+    int ignore_bottom_;
+
+    enum Direction { LEFT, UP, RIGHT, DOWN };
+
+    Direction direction_;
+    int delta_x_;
+    int delta_y_;
+    int current_step_;
+    int horizontal_step_count_;
+    int vertical_step_count_;
+  };
+
  private:
   void AssertTile(int i, int j) const {
     DCHECK_GE(i,  0);