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 28 matching lines @@
     /**
      *  Clean up after reading/skipping scanlines.
      *
      *  It is possible that not all scanlines will have been read/skipped.  In
      *  fact, in the case of subset decodes, it is likely that there will be
      *  scanlines at the bottom of the image that have been ignored.
      */
     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; }
 
     /**
      *  Initialize on the first scanline, with the specified options.
      *
      *  This must be called in order to call getScanlnies or skipScanlines. If
      *  it has been called before, this will require rewinding the stream.
      *
@@ skipping 69 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();
     }
 
+    /**
+     *  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:
     const SkImageInfo   fSrcInfo;
     SkImageInfo         fDstInfo;
     int                 fCurrScanline;
 
     virtual SkCodec::Result onStart(const SkImageInfo& dstInfo,
                                     const SkCodec::Options& options,
                                     SkPMColor ctable[], int* ctableCount) = 0;
 
     // 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