Add scaled subset API to SkCodec

include/codec/SkScaledCodec.h

Index: include/codec/SkScaledCodec.h
diff --git a/include/codec/SkScaledCodec.h b/include/codec/SkScaledCodec.h
index 028706bc9400bfb7028ba75699029d2454277484..969846b7b5633940e586aefbfbb95f046088e483 100644
--- a/include/codec/SkScaledCodec.h
+++ b/include/codec/SkScaledCodec.h
@@ -33,6 +33,9 @@ protected:
      */
     SkISize onGetScaledDimensions(float desiredScale) const override;
     bool onDimensionsSupported(const SkISize&) override;
+    bool onSubsetSupported(const SkIRect&, bool) override { return true; }
+    bool onScaledSubsetSupported(const Options&, bool) override;
+    bool onGetScaledSubsetDimensions(float desiredScale, const Options& options) const override;
 
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*, int*)
             override;
@@ -50,6 +53,42 @@ protected:
 
 private:
 
+    /**
+     * Perform the decode with scaling handled by the native codec.
+     * Assumes startScanlineDecoder() has already been called.
+     *
+     * @param scaledInfo       Destination image info, containing dimensions that
+     *                         represent the full size image, scaled to the desired
+     *                         scale, before any subset has been applied.
+     * @param dst              Pointer to destination pixel memory.
+     * @param rowBytes         Stride length in destination memory.
+     * @param scaledSubsetRect Desired subset in terms of the scaled dimensions.
+     * @param zeroInit         Indicates if destination memory is zero initialized.
+     * @param rowsDecoded      Out parameter to specify how many rows were
+     *                         successfully decoded on an incomplete decode.
+     */
+    Result nativeDecode(const SkImageInfo& scaledInfo, void* dst, size_t rowBytes,
+            const SkIRect& scaledSubsetRect, ZeroInitialized zeroInit, int* rowsDecoded);
+
+    /**
+     * Perform the decode with sampling as the scaling method.
+     * Assumes startScanlineDecoder() has already been called.
+     *
+     * @param scaledSubsetInfo Destination image info, containing dimensions that
+     *                         represent the scaled and subsetted result.
+     * @param dst              Pointer to destination pixel memory.
+     * @param rowBytes         Stride length in destination memory.
+     * @param subsetRect       Desired subset in terms of the original dimensions.
+     * @param sampleX          Sample factor in the x-dimension.
+     * @param sampleY          Sample factor in the y-dimension.
+     * @param zeroInit         Indicates if destination memory is zero initialized.
+     * @param rowsDecoded      Out parameter to specify how many rows were
+     *                         successfully decoded on an incomplete decode.
+     */
+    Result sampledDecode(const SkImageInfo& scaledSubsetInfo, void* dst, size_t rowBytes,
+            const SkIRect& subsetRect, int sampleX, int sampleY, ZeroInitialized zeroInit,
+            int* rowsDecoded);
+
     SkAutoTDelete<SkCodec> fCodec;
 
     explicit SkScaledCodec(SkCodec*);