Break up SkLazyPixelRef functionally into class hierarchy.

src/lazy/SkCachingPixelRef.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 SkCachingPixelRef_DEFINED
+#define SkCachingPixelRef_DEFINED
+
+#include "SkImage.h"
+#include "SkPixelRef.h"
+
+class SkColorTable;
+
+/**
+ *  PixelRef which defers decoding until SkBitmap::lockPixels() is
+ *  called.  Caches the decoded images in the global
+ *  SkScaledImageCache.  When the pixels are unlocked, this cache may
+ *  or be destroyed before the next lock.  If so, onLockPixels will
+ *  attempt to re-decode.
+ *
+ *  Decoding is handled by the pure-virtual functions onDecodeInfo()
+ *  and onDecode().  Subclasses of this class need only provide those
+ *  two functions.
+ */
+class SkCachingPixelRef : public SkPixelRef {
+public:
+    explicit SkCachingPixelRef();

[reed1, 2013/11/04 14:49:06]

don't need this word if there is no parameter

[hal.canary, 2013/11/04 15:25:22]

Done.

+    virtual ~SkCachingPixelRef();
+
+protected:
+    virtual void* onLockPixels(SkColorTable** colorTable) SK_OVERRIDE;
+    virtual void onUnlockPixels() SK_OVERRIDE;
+    virtual bool onLockPixelsAreWritable() const SK_OVERRIDE { return false; }
+    virtual bool onImplementsDecodeInto() SK_OVERRIDE  { return true; }
+    virtual bool onDecodeInto(int pow2, SkBitmap*) SK_OVERRIDE;
+
+    /**
+     *  Configure the supplied bitmap for this pixelRef, based on
+     *  information provided by onDecodeInfo().  Does not set the
+     *  bitmap's pixelRef. */
+    bool configure(SkBitmap* bitmap);
+
+    /**
+     *  Cache info from onDecodeInfo(). Returns NULL on failure.
+     */
+    const SkImageInfo* getInfo();
+
+    /**
+     *  Return some information about the pixels, allowing this class
+     *  to allocate pixels.  @return false if anything goes wrong.
+     */
+    virtual bool onDecodeInfo(SkImageInfo* info) = 0;
+    /**
+     *  Decode into the given pixels, a block of memory of size
+     *  (info->fHeight * rowBytes) bytes.  Should follow the format
+     *  reported by onDecodeInfo().
+     *  @return false if anything goes wrong.
+     */
+    virtual bool onDecode(void* pixels, size_t rowBytes) = 0;

[reed1, 2013/11/04 14:49:06]

nit: I think onDecodePixels would be clearer, since we have been using modifiers
after onDecode... for other virtuals.

in a different conversation w/ leon, we discussed the idea of passing in Info as
input to this call, to help debugger so the impl can confirm that the caller
knows what its asking for (config, size).

e.g.

onDecodePixels(const SkImageInfo&, void* pixels, size_t rowBytes)

Such a contract also allows us to have the caller's info specify different
output-configs, which the impl can decide to support or not.

[hal.canary, 2013/11/04 15:25:22]

Done

+
+private:
+    bool                        fErrorInDecoding;
+    void*                       fScaledCacheId;
+    SkImageInfo                 fInfo;
+
+    typedef SkPixelRef INHERITED;
+};
+
+#endif  // SkCachingPixelRef_DEFINED
+