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 SkDiscardablePixelRef to decode and

[scroggo, 2013/11/20 14:21:53]

Since this is an interface that does not necessarily use an
SkDiscardablePixelRef, I think "purgeable PixelRef" is better.

+ *  re-decode an image as needed.
+ */
+class SkImageGenerator {
+public:
+    /**
+     *  The SkDiscardablePixelRef which takes ownership of this
+     *  SkImageGenerator will call the image generator's destructor.
+     */
+    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 of
+     *  this object 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

[scroggo, 2013/11/20 14:21:53]

I still think this line should be changed, since the interface does not require
info to be identical to the result of getInfo, and an implementation might allow
an info that is not identical.

+     *         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