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..ffe032b26c60bc94fe1752c393ad25446ea70087 100644
--- a/include/codec/SkScanlineDecoder.h
+++ b/include/codec/SkScanlineDecoder.h
@@ -46,6 +46,17 @@ 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

[scroggo, 2015/08/06 15:09:10]

Maybe this should have a FIXME: share this with SkCodec?

I just filed skbug.com/4175 to track the changing relationship between SkCodec
and SkScanlineDecoder. Right now I'm toying with the idea of an abstract
interface that is implemented by both that holds the common methods etc (which I
also mention in that bug).

[emmaleer, 2015/08/06 18:59:52]

Acknowledged.

+     */
+    SkISize getScaledDimensions(float desiredScale) {
+        return this->onGetScaledDimensions(desiredScale);
+    }
+
+    /**
      *  Returns the default info, corresponding to the encoded data.
      */
     const SkImageInfo& getInfo() { return fSrcInfo; }
@@ -135,14 +146,44 @@ 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: