Add SkImageGenerator Interface

include/core/SkImageGenerator.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkImageGenerator_DEFINED
+#define SkImageGenerator_DEFINED
+
+#include "SkImageInfo.h"
+
+class SkData;
+
+/**
+ * An interface that allows a purgable PixelRef to re-decode an image.
+ */
+class SkImageGenerator {
+public:
+    virtual ~SkImageGenerator();
+
+    /**
+     *  Return a ref to the encoded (i.e. compressed) representation,
+     *  of this data.
+     *
+     *  If non-NULL is returned, the caller is responsible for calling
+     *  unref() on the data when it is finished.
+     */
+    virtual SkData* refEncodedData() { return NULL; }
+
+    /**
+     *  Return some information about the image, allowing the owner fo
+     *  this ojbect to allocate pixels.
+     *
+     *  @return false if anything goes wrong.
+     */
+    virtual bool getInfo(SkImageInfo* info) = 0;
+
+    /**
+     *  Decode into the given pixels, a block of memory of size at
+     *  least (info.fHeight - 1) * rowBytes + (info.fWidth *
+     *  bytesPerPixel)
+     *
+     *  @param info Should be identical to the info returned by
+     *         getInfo so that the implementation can confirm that the
+     *         caller knows what it is asking for (config, size).
+     *         This contract also allows the caller to specify
+     *         different output-configs, which the implementation can
+     *         decide to support or not.
+     *
+     *  @return false if anything goes wrong.
+     */
+    virtual bool getPixels(const SkImageInfo& info,
+                           void* pixels,
+                           size_t rowBytes) = 0;
+};
+
+#endif  // SkImageGenerator_DEFINED