Teach Skia to use discardable memory

Source/core/platform/graphics/DecodingImageGenerator.h

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-#ifndef MockDiscardablePixelRef_h
+#ifndef DecodingImageGenerator_h
+#define DecodingImageGenerator_h
 
-#include "SkBitmap.h"
-#include "SkPixelRef.h"
+#include "SkImageGenerator.h"
+#include "SkImageInfo.h"
+
+#include "wtf/RefPtr.h"
+
+class SkData;
 
 namespace WebCore {
 
-class MockDiscardablePixelRef : public SkPixelRef {
+class ImageFrameGenerator;
+
+// Implements SkImageGenerator and used by SkPixelRef to populate a discardable
+// memory with decoded pixels.
+//
+// This class does not own an ImageDecode. It does not own encoded data. It serves
+// as and adapter to ImageFrameGenerator which actually performs decoding.

[Stephen White, 2013/12/05 21:52:14]

Naming nit: if it's an adapter, maybe it should have Adapter in the name?

[Alpha Left Google, 2013/12/08 00:30:11]

I prefer to keep this name. It sounds awkward to call this
ImageGeneratorAdapter. 

+class DecodingImageGenerator : public SkImageGenerator {
 public:
-    MockDiscardablePixelRef() : discarded(false) { setURI("discardable"); }
-    ~MockDiscardablePixelRef() { }
+    DecodingImageGenerator(PassRefPtr<ImageFrameGenerator>, const SkImageInfo&, size_t index);
+    virtual ~DecodingImageGenerator();
 
-    void discard()
-    {
-        ASSERT(!m_lockedMemory);
-        discarded = true;
-    }
-
-    SK_DECLARE_UNFLATTENABLE_OBJECT()
-
-protected:
-    // SkPixelRef implementation.
-    virtual void* onLockPixels(SkColorTable**)
-    {
-        if (discarded)
-            return 0;
-        m_lockedMemory = &discarded;
-        return m_lockedMemory;
-    }
-
-    virtual void onUnlockPixels()
-    {
-        m_lockedMemory = 0;
-    }
+    // SkImageGenerator implementation.
+    virtual SkData* refEncodedData();
+    virtual bool getInfo(SkImageInfo*);
+    virtual bool getPixels(const SkImageInfo&, void* pixels, size_t rowBytes);
 
 private:
-    void* m_lockedMemory;
-    bool discarded;
+    RefPtr<ImageFrameGenerator> m_frameGenerator;
+    SkImageInfo m_imageInfo;
+    size_t m_frameIndex;
 };
 
 } // namespace WebCore
 
-#endif // MockDiscardablePixelRef_h
+#endif // DecodingImageGenerator_h_