SkScaledCodec class

include/codec/SkScanlineDecoder.h

Index: include/codec/SkScanlineDecoder.h
diff --git a/include/codec/SkScanlineDecoder.h b/include/codec/SkScanlineDecoder.h
index 8376e57c09d84bb48c1d7ae295ccd441a7feab48..3854f05a7118397ef6a9795b9c554d8a2ef044f6 100644
--- a/include/codec/SkScanlineDecoder.h
+++ b/include/codec/SkScanlineDecoder.h
@@ -75,6 +75,18 @@ public:
         return this->onReallyHasAlpha();
     }
 
+    /**
+     * 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& requested)
         : fDstInfo(requested)
@@ -82,6 +94,12 @@ protected:
 
     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: