SkScaledCodec class

include/codec/SkScanlineDecoder.h

Index: include/codec/SkScanlineDecoder.h
diff --git a/include/codec/SkScanlineDecoder.h b/include/codec/SkScanlineDecoder.h
index c233663dbdb2d216349eed791744e20eec060f3f..c547f6701f667d2ecfd61f7dca2154f164c19242 100644
--- a/include/codec/SkScanlineDecoder.h
+++ b/include/codec/SkScanlineDecoder.h
@@ -46,6 +46,18 @@ public:
     virtual ~SkScanlineDecoder() {}
 
     /**
+     *  Return a size that approximately supports the desired scale factor.
+     *  The codec may not be able to scale efficiently to the exact scale
+     *  factor requested, so return a size that approximates that scale.
+     *  The returned value is the codec's suggestion for the closest valid
+     *  scale that it can natively support
+     *  FIXME: share this with SkCodec
+     */
+    SkISize getScaledDimensions(float desiredScale) {
+        return this->onGetScaledDimensions(desiredScale);
+    }
+
+    /**
      *  Returns the default info, corresponding to the encoded data.
      */
     const SkImageInfo& getInfo() { return fSrcInfo; }
@@ -135,14 +147,44 @@ public:
         return this->onReallyHasAlpha();
     }
 
+    /**
+     *  Format of the encoded data.
+     */
+    SkEncodedFormat getEncodedFormat() const { return this->onGetEncodedFormat(); }
+
+    /**
+     * returns true if the image must be scaled, in the y direction, after reading, not during.
+     * To scale afterwards, we first decode every line and then sample the lines we want afterwards.
+     * An example is interlaced pngs, where calling getScanlines once (regardless of the count
+     * used) needs to read the entire image, therefore it is inefficient to call
+     * getScanlines more than once. Instead, it should only ever be called with all the
+     * rows needed.
+     */
+    bool requiresPostYSampling() {
+        return this->onRequiresPostYSampling();
+    }
+
 protected:
     SkScanlineDecoder(const SkImageInfo& srcInfo)
         : fSrcInfo(srcInfo)
         , fDstInfo()
         , fCurrScanline(0) {}
 
+    virtual SkISize onGetScaledDimensions(float /* desiredScale */) {
+        // By default, scaling is not supported.
+        return this->getInfo().dimensions();
+    }
+
+    virtual SkEncodedFormat onGetEncodedFormat() const = 0;
+
     virtual bool onReallyHasAlpha() const { return false; }
 
+    /**
+     * returns true if the image type is hard to sample and must be scaled after reading, not during
+     * An example is interlaced pngs, where the entire image must be read for each decode
+     */
+    virtual bool onRequiresPostYSampling() { return false; }
+
     const SkImageInfo& dstInfo() const { return fDstInfo; }
 
 private: