cc: Make visible rect computation aware of pixel-moving filters

cc/trees/clip_expander.h

Index: cc/trees/clip_expander.h
diff --git a/cc/trees/clip_expander.h b/cc/trees/clip_expander.h
new file mode 100644
index 0000000000000000000000000000000000000000..4ddad78ec8d02d173f969aa29a5dc2e9fd13c6c4
--- /dev/null
+++ b/cc/trees/clip_expander.h
@@ -0,0 +1,51 @@
+// 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_EXPANDER_H_
+#define CC_TREES_CLIP_EXPANDER_H_
+
+#include "cc/base/cc_export.h"
+#include "ui/gfx/geometry/rect.h"
+
+namespace gfx {
+class Transform;
+}
+
+namespace cc {
+
+class PropertyTrees;
+
+class CC_EXPORT ClipExpander {
+ public:
+  enum class ExpanderType { FILTER };
+
+  ClipExpander(ExpanderType type, int filter_effect_id);

[weiliangc, 2016/10/31 18:20:25]

Is there an expander type that is not Filter that we want to add later?

[ajuma, 2016/10/31 18:28:05]

Yeah, I believe there are other kinds of expanding effects we'll need to handle
(like the pixel-snapping type effects that the paint folks were mentioning a
couple weeks ago). Leaving in the type for now makes it easier to add those (and
if it turns out that none get added we can just delete it later).

+  ClipExpander(const ClipExpander& other);
+
+  bool operator==(const ClipExpander& other) const;
+
+  bool operator!=(const ClipExpander& other) const { return !(*this == other); }
+
+  // Maps "forward" to determine which pixels in a destination rect are affected
+  // by pixels in the given source rect.
+  gfx::Rect MapRect(const gfx::Rect& rect,
+                    const PropertyTrees* property_trees) const;
+
+  // Maps "backward" to determine which pixels in the source affect the pixels
+  // in the given destination rect.
+  gfx::Rect MapRectReverse(const gfx::Rect& rect,
+                           const PropertyTrees* property_trees) const;
+
+  // The id of the effect node in whose transform space the expansion happens.
+  int target_effect_id() const { return target_effect_id_; }
+
+ private:
+  ExpanderType expander_type_;
+
+  int target_effect_id_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_CLIP_EXPANDER_H_