SkScaledCodec class

include/codec/SkScanlineDecoder.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkScanlineDecoder_DEFINED
 #define SkScanlineDecoder_DEFINED
 
@@ skipping 57 matching lines @@
      *  of the encoded data, but then never use any colors which have alpha
      *  less than 100%. This function can be called *after* decoding to
      *  determine if such an image truly had alpha. Calling it before decoding
      *  is undefined.
      *  FIXME: see skbug.com/3582.
      */
     bool reallyHasAlpha() const {
         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)
         , fCurrScanline(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 onIsHardToSample() { return false; }
+
     const SkImageInfo& dstInfo() const { return fDstInfo; }
 
 private:
     const SkImageInfo   fDstInfo;
     int                 fCurrScanline;
 
     // Naive default version just calls onGetScanlines on temp memory.
     virtual SkCodec::Result onSkipScanlines(int countLines) {
         SkAutoMalloc storage(fDstInfo.minRowBytes());
         // Note that we pass 0 to rowBytes so we continue to use the same memory.
         // Also note that while getScanlines checks that rowBytes is big enough,
         // onGetScanlines bypasses that check.
         // Calling the virtual method also means we do not double count
         // countLines.
         return this->onGetScanlines(storage.get(), countLines, 0);
     }
 
     virtual SkCodec::Result onGetScanlines(void* dst, int countLines,
                                                     size_t rowBytes) = 0;
 
 };
 #endif // SkScanlineDecoder_DEFINED