Break up SkLazyPixelRef functionally into class hierarchy.

src/lazy/SkCachingPixelRef.h

+/*
+ * Copyright 2012 Google Inc.

[scroggo, 2013/10/31 21:53:06]

2013

[hal.canary, 2013/11/01 03:29:24]

Done.

+ *
+ * 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"
+#include "SkFlattenable.h"
+#include "SkScaledImageCache.h"
+
+class SkColorTable;
+class SkImageCache;
+
+/**
+ *  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, the image will be

[scroggo, 2013/10/31 21:53:06]

or may not*

[hal.canary, 2013/11/01 03:29:24]

Done.

+ *  re-decoded.
+ *
+ *  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:
+    /**
+     *  Create a new SkCachingPixelRef.  If cache is NULL, use the
+     *  default global cache.
+     *
+     *  Allowing the use of a non-global cache is useful for testing.
+     */
+    explicit SkCachingPixelRef(SkScaledImageCache* cache = NULL);

[scroggo, 2013/10/31 21:53:06]

It may be obvious, but should we point out that SkCachingPixelRef does not take
ownership of cache?

[hal.canary, 2013/11/01 03:29:24]

Done.

+    virtual ~SkCachingPixelRef();
+
+    // No need to flatten this object. When flattening an SkBitmap,
+    // SkOrderedWriteBuffer will check the encoded data and write that

[scroggo, 2013/10/31 21:53:06]

This statement is only true if you have implemented onRefEncodedData.

[hal.canary, 2013/11/01 03:29:24]

I'll remove this section for now.  Since this is an abstract class, I'm not sure
it matters.

+    // instead.  Future implementations of SkFlattenableWriteBuffer
+    // will need to special case for onRefEncodedData as well.
+    SK_DECLARE_UNFLATTENABLE_OBJECT()
+
+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);
+
+    /**
+     * Return some information about the pixels, allowing this class
+     * to allocate pixels.  @return false if anything goes wrong.
+     */
+    virtual bool onDecodeInfo(SkISize*,
+                              SkBitmap::Config*,
+                              SkAlphaType*) = 0;
+    /**
+     * Decode into the given pixels, a block of memory of size
+     * (size->fHeight * fRowBytes) bytes.
+     * @return false if anything goes wrong.
+     */
+    virtual bool onDecode(void* pixels, size_t rowBytes) = 0;
+
+private:
+    bool                        fErrorInDecoding;
+    SkScaledImageCache*         fCache;
+    SkScaledImageCache::ID*     fScaledCacheId;
+    SkISize                     fBitmapSize;

[scroggo, 2013/10/31 21:53:06]

Why do you have these three instead of an SkImage::Info?

[hal.canary, 2013/11/01 03:29:24]

I wanted to keep the onDecodeInfo() interface simple.  These are exactly the
parameters I need to call bitmap.setConfig(...)

And I want this general-purpose interface to be able to produce any valid
bitmap.

[scroggo, 2013/11/01 15:48:00]

Wouldn't

bool onDecodeInfo(SkImage::Info*)

be simpler than

bool onDecodeInfo(SkISize*, SkBitmap::Config*, SkAlphaType*)

?
Does using an SkImage::Info mean that it's less general-purpose or it cannot
produce some valid bitmap?

+    SkBitmap::Config            fBitmapConfig;
+    SkAlphaType                 fBitmapAlphaType;
+
+    // lazily initialized our cached info. Returns NULL on failure.

[scroggo, 2013/10/31 21:53:06]

Returns false on failure.

[hal.canary, 2013/11/01 03:29:24]

Done.

+    bool updateInfo();
+
+    typedef SkPixelRef INHERITED;
+};
+
+#endif  // SkCachingPixelRef_DEFINED