Add support for multiple frames in SkCodec

src/codec/SkCodecAnimation.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/*
+ * Copyright (C) 2015 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef SkCodecAnimation_DEFINED
+#define SkCodecAnimation_DEFINED
+
+#include "SkCodec.h"
+#include "SkRect.h"
+
+class SkCodecAnimation {
+public:
+
+    // GIF and WebP support animation. The explanation below is in terms of GIF,
+    // but the same constants are used for WebP, too.
+    // GIFs have an optional 16-bit unsigned loop count that describes how an
+    // animated GIF should be cycled.  If the loop count is absent, the animation
+    // cycles once; if it is 0, the animation cycles infinitely; otherwise the
+    // animation plays n + 1 cycles (where n is the specified loop count).  If the
+    // GIF decoder defaults to kAnimationLoopOnce in the absence of any loop count
+    // and translates an explicit "0" loop count to kAnimationLoopInfinite, then we
+    // get a couple of nice side effects:
+    //   * By making kAnimationLoopOnce be 0, we allow the animation cycling code to
+    //     avoid special-casing it, and simply treat all non-negative loop counts
+    //     identically.
+    //   * By making the other two constants negative, we avoid conflicts with any
+    //     real loop count values.
+    static const int kAnimationLoopOnce = 0;
+    static const int kAnimationLoopInfinite = -1;
+    static const int kAnimationNone = -2;
+
+    /**
+     *  This specifies how the next frame is based on this frame.
+     *
+     *  Names are based on the GIF 89a spec.
+     *
+     *  The numbers correspond to values in a GIF.
+     */
+    enum DisposalMethod {
+        /**
+         *  The next frame should be drawn on top of this one.
+         *
+         *  In a GIF, a value of 0 (not specified) is also treated as Keep.
+         */
+        Keep_DisposalMethod             = 1,
+
+        /**
+         *  Similar to Keep, except the area inside this frame's rectangle
+         *  should be cleared to the BackGround color (transparent) before
+         *  drawing the next frame.
+         */
+        RestoreBGColor_DisposalMethod   = 2,
+
+        /**
+         *  The next frame should be drawn on top of the previous frame - i.e.
+         *  disregarding this one.
+         *
+         *  In a GIF, a value of 4 is also treated as RestorePrevious.
+         */
+        RestorePrevious_DisposalMethod  = 3,
+    };
+
+private:
+    SkCodecAnimation();
+};
+#endif // SkCodecAnimation_DEFINED