Option for SkCodec to treat dst as all zeroes.

include/codec/SkCodec.h

Index: include/codec/SkCodec.h
diff --git a/include/codec/SkCodec.h b/include/codec/SkCodec.h
index beb9cb97b32bdb51bed7cc4d76d24b968fe0858d..da55ea8d2044f008b79be1787c71743522c81134 100644
--- a/include/codec/SkCodec.h
+++ b/include/codec/SkCodec.h
@@ -48,6 +48,38 @@ public:
      */
     SkISize getScaledDimensions(float desiredScale) const;
 
+    /**
+     *  Whether or not the memory passed to getPixels is zero initialized.
+     */
+    enum ZeroInitialized {

[scroggo, 2015/03/05 16:12:23]

I decided to go with ZeroInitialized instead of SkipZeroes, since the decoder
may not skip zeroes. This seems more accurate as to what's going on.

That said, it may be that a caller happened to use zero initialized memory, but
there's very few zero pixels, so it's not worth skipping. In that case, they
could just not set it to kYes, even though it's technically not true.

+        /**
+         *  The memory passed to getPixels is zero initialized. The SkCodec
+         *  may take advantage of this by skipping writing zeroes.
+         */
+        kYes_ZeroInitialized,
+        /**
+         *  The memory passed to getPixels has not been initialized to zero,
+         *  so the SkCodec must write all zeroes to memory.
+         *
+         *  This is the default.
+         */
+        kNo_ZeroInitialized,
+    };
+
+    /**
+     *  Specify whether this SkCodec should treat the memory passed to
+     *  getPixels as zero initialized.
+     *
+     *  The default is No.
+     */
+    void setZeroInitialized(ZeroInitialized zero) { fZeroInitialized = zero; }

[scroggo, 2015/03/05 16:12:23]

It probably makes sense to include this as part of getPixels, although getPixels
already has a long parameter list, and I don't know that this is relevant for
other SkImageGenerators.

+
+    /**
+     *  Return whether this SkCodec considers memory passed to getPixels as
+     *  zero initialized.
+     */
+    ZeroInitialized getZeroInitialized() const { return fZeroInitialized; }
+
 protected:
     SkCodec(const SkImageInfo&, SkStream*);
 
@@ -85,8 +117,9 @@ protected:
     bool SK_WARN_UNUSED_RESULT rewindIfNeeded();
 
 private:
-    const SkImageInfo fInfo;
+    const SkImageInfo       fInfo;
     SkAutoTDelete<SkStream> fStream;
-    bool fNeedsRewind;
+    bool                    fNeedsRewind;
+    ZeroInitialized         fZeroInitialized;
 };
 #endif // SkCodec_DEFINED