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..2dd63639bebc755b4659115175fe2df8e5d9623f 100644
--- a/include/codec/SkScanlineDecoder.h
+++ b/include/codec/SkScanlineDecoder.h
@@ -75,6 +75,17 @@ public:
         return this->onReallyHasAlpha();
     }
 
+    /**
+     * returns true if the image type is hard to sample and must be scaled after reading, not during
+     * 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 isHardToSample() {

[djsollen, 2015/08/03 13:13:59]

isInterlaced?

[emmaleer, 2015/08/03 14:29:41]

This function return's whether we can sample normally, or if we have to decode
every line and then sample afterwards.
Interlaced png's is one example, but there may be others in the future.
Also, other types of interlaced images, such as gif and jpeg, can be scaled
normally.
Options for the name so far are: canSampleMidway, requiresPostSampling, and
isHardToSample.
Matt and I were talking, and think requiresPostSampling might work.
I'm going to ask Leon what he thinks, and then will change the name.
If you have any better suggestions for a name, please let me know.

+        return this->onIsHardToSample();
+    }
+
 protected:
     SkScanlineDecoder(const SkImageInfo& requested)
         : fDstInfo(requested)
@@ -82,6 +93,12 @@ 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 onIsHardToSample() { return false; }
+
     const SkImageInfo& dstInfo() const { return fDstInfo; }
 
 private: