Move PixelRefMap and its Iterator out from Picture class

cc/resources/pixel_ref_map.h

Index: cc/resources/pixel_ref_map.h
diff --git a/cc/resources/pixel_ref_map.h b/cc/resources/pixel_ref_map.h
new file mode 100644
index 0000000000000000000000000000000000000000..fbc8953b58b479300304cf2173979cfaa693e7bd
--- /dev/null
+++ b/cc/resources/pixel_ref_map.h
@@ -0,0 +1,85 @@
+// Copyright 2015 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_RESOURCES_PIXEL_REF_MAP_H_
+#define CC_RESOURCES_PIXEL_REF_MAP_H_
+
+#include <utility>
+#include <vector>
+
+#include "base/containers/hash_tables.h"
+#include "base/lazy_instance.h"
+#include "base/memory/ref_counted.h"
+#include "cc/base/cc_export.h"
+#include "third_party/skia/include/core/SkPicture.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/size.h"
+
+class SkPixelRef;
+
+namespace cc {
+
+class Picture;
+
+typedef std::pair<int, int> PixelRefMapKey;
+typedef std::vector<SkPixelRef*> PixelRefs;
+
+// This class is used and owned by cc Picture class. It is used to gather pixel
+// refs which would happen after record. It takes in |cell_size| to decide how
+// big each grid cell should be.
+class CC_EXPORT PixelRefMap : public base::hash_map<PixelRefMapKey, PixelRefs> {

[vmpstr, 2015/03/05 19:31:44]

I find this kinda iffy. Is it difficult to have a private hash map instead and
provide some accessor functions that base::hash_map would provide? I don't think
we use too many of those, do we? 

The problem is that it would be possible to implicitly convert this to a
base::hash_map pointer (suppose someone assumes incorrectly that PixelRefMap is
a typedef to base::hash_map), and then destruction would yield UD, since I don't
think base::hash_map has a virtual dtor.

[weiliangc, 2015/03/09 18:50:21]

Accessing hash_map is way less often than I expected. Thanks for the point about
desctructor!

Done.

+ public:
+  explicit PixelRefMap(const gfx::Size& cell_size);
+  ~PixelRefMap();
+  void GatherPixelRefsFromPicture(SkPicture* picture);
+
+ private:
+  gfx::Point min_pixel_cell_;
+  gfx::Point max_pixel_cell_;
+  gfx::Size cell_size_;
+
+  friend class PixelRefMapIterator;
+};
+
+// This iterator imprecisely returns the set of pixel refs that are needed to
+// raster this layer rect from this picture.  Internally, pixel refs are
+// clumped into tile grid buckets, so there may be false positives.
+class CC_EXPORT PixelRefMapIterator {

[vmpstr, 2015/03/05 19:31:44]

This can also be PixelRefMap::Iterator, which might be more explicit in what it
iterates? Up to you though.

[weiliangc, 2015/03/09 18:50:21]

Moved to PixelRefMap::Iterator.

Before when PixelRefMap inherits hash_map compiler would complain about
::Iterator. So it works out.

+ public:
+  // Default iterator constructor that is used as place holder for invalid
+  // PixelRefMapIterator.
+  PixelRefMapIterator();
+  PixelRefMapIterator(const gfx::Rect& layer_rect, const Picture* picture);
+  ~PixelRefMapIterator();
+
+  SkPixelRef* operator->() const {
+    DCHECK_LT(current_index_, current_pixel_refs_->size());
+    return (*current_pixel_refs_)[current_index_];
+  }
+
+  SkPixelRef* operator*() const {
+    DCHECK_LT(current_index_, current_pixel_refs_->size());
+    return (*current_pixel_refs_)[current_index_];
+  }
+
+  PixelRefMapIterator& operator++();
+  operator bool() const { return current_index_ < current_pixel_refs_->size(); }
+
+ private:
+  static base::LazyInstance<PixelRefs> empty_pixel_refs_;
+  const PixelRefMap* map_;
+  const PixelRefs* current_pixel_refs_;
+  unsigned current_index_;
+
+  gfx::Rect layer_rect_;
+
+  gfx::Point min_point_;
+  gfx::Point max_point_;
+  int current_x_;
+  int current_y_;
+};
+
+}  // namespace cc
+
+#endif  // CC_RESOURCES_PIXEL_REF_MAP_H_