SkScaledCodec class

include/codec/SkCodec.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 SkCodec_DEFINED
 #define SkCodec_DEFINED
 
@@ skipping 34 matching lines @@
 
     /**
      *  Return the ImageInfo associated with this codec.
      */
     const SkImageInfo& getInfo() const { return fInfo; }
 
     /**
      *  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
      */
     SkISize getScaledDimensions(float desiredScale) const {
         return this->onGetScaledDimensions(desiredScale);
     }
 
+    /*
+     * Checks if we can patially natively scale to the desiredScale, and partially natively scales

[scroggo, 2015/08/04 20:05:21]

"partially" is missing r (the first time)

[emmaleer, 2015/08/05 14:47:51]

Acknowledged.

+     * the dimensions if possible.
+     * Returns the new sampleSize, which is used to finish scaling to the desiredScale.
+     * Ex: desiredScale = 1/6. Natively can scale by 1/2. New sampleSize = 3, as there is still
+     * 1/3 scaling left to do, which is done by sampling.
+     * Returns -1 if partial native scaling is not supported.
+     */
+    int partiallyNativelyScale(float desiredScale) {

[scroggo, 2015/08/04 20:05:21]

I'm not a huge fan of this name. I am not sure I have a better name though. This
does the following:

A) Tells the codec to scale
B) Returns the sample size needed afterwards

On a related note, this function behaves a lot differently from the other
functions. Although I've been arguing recently that SkCodec is not really
stateless, the only state it currently has is related to the stream - no other
APIs should change future function calls.

This function also feels like it leaks a lot of SkScaledCodec into SkCodec and
SkJpegCodec.

Right now I'm leaning towards removing the partial scaling, with a TODO and a
bug to do it later.

[emmaleer, 2015/08/05 14:47:51]

Okay, I'll first upload the changes for future reference, then remove partial
scaling. 

+        return this->onPartiallyNativelyScale(desiredScale);
+    }
+
     /**
      *  Return (via desiredSubset) a subset which can decoded from this codec,
      *  or false if this codec cannot decode subsets or anything similar to
      *  desiredSubset.
      *
      *  @param desiredSubset In/out parameter. As input, a desired subset of
      *      the original bounds (as specified by getInfo). If true is returned,
      *      desiredSubset may have been modified to a subset which is
      *      supported. Although a particular change may have been made to
      *      desiredSubset to create something supported, it is possible other
@@ skipping 175 matching lines @@
     }
 
 protected:
     SkCodec(const SkImageInfo&, SkStream*);
 
     virtual SkISize onGetScaledDimensions(float /* desiredScale */) const {
         // By default, scaling is not supported.
         return this->getInfo().dimensions();
     }
 
+    virtual int onPartiallyNativelyScale(float desiredScale) {
+        return -1;
+    }
     virtual SkEncodedFormat onGetEncodedFormat() const = 0;
 
     virtual Result onGetPixels(const SkImageInfo& info,
                                void* pixels, size_t rowBytes, const Options&,
                                SkPMColor ctable[], int* ctableCount) = 0;
 
     virtual bool onGetValidSubset(SkIRect* /* desiredSubset */) const {
         // By default, subsets are not supported.
         return false;
     }
@@ skipping 51 matching lines @@
     SkStream* stream() {
         return fStream.get();
     }
 
 private:
     const SkImageInfo       fInfo;
     SkAutoTDelete<SkStream> fStream;
     bool                    fNeedsRewind;
 };
 #endif // SkCodec_DEFINED