diff -r 000000000000 -r 6474c204b198 gfx/skia/trunk/include/images/SkPageFlipper.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/skia/trunk/include/images/SkPageFlipper.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,62 @@
+
+/*
+ * Copyright 2008 The Android Open Source Project
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#ifndef SkPageFlipper_DEFINED
+#define SkPageFlipper_DEFINED
+
+#include "SkRegion.h"
+
+/** SkPageFlipper manages alternating inval/dirty regions for a rectangular area
+    (like a bitmap). You call inval() to accumulate inval areas, and then when
+    you're ready to "flip" pages (i.e. draw into the one you've been
+    invalidating) you call update, which swaps the inval regions, and returns
+    two things to you: 1) the final inval region to be drawn into, and 2) the
+    region of pixels that should be copied from the "front" page onto the one
+    you're about to draw into. This copyBits region will be disjoint from the
+    inval region, so both need to be handled.
+ */
+class SkPageFlipper {
+public:
+    SkPageFlipper();
+    SkPageFlipper(int width, int height);
+
+    int width() const { return fWidth; }
+    int height() const { return fHeight; }
+
+    void resize(int width, int height);
+
+    bool isDirty() const { return !fDirty1->isEmpty(); }
+    const SkRegion& dirtyRgn() const { return *fDirty1; }
+
+    void inval();
+    void inval(const SkIRect&);
+    void inval(const SkRegion&);
+    void inval(const SkRect&, bool antialias);
+
+    /** When you're ready to write to the back page, call update. The returned
+        region is the invalidate are that needs to be drawn to. The copyBits
+        region (provided by the caller) is the area that should be copied from
+        the front page to the back page (will not intersect with the returned
+        inval region.
+
+        Once this is called, the two internal regions are swapped, so the *new*
+        back inval region is ready to receive new inval calls.
+     */
+    const SkRegion& update(SkRegion* copyBits);
+
+private:
+    SkRegion*   fDirty0;
+    SkRegion*   fDirty1;
+    SkRegion    fDirty0Storage;
+    SkRegion    fDirty1Storage;
+    int         fWidth;
+    int         fHeight;
+};
+
+#endif