Add subsetting to SkScanlineDecoder

src/codec/SkCodecPriv.h

 /*
  * Copyright 2015 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCodecPriv_DEFINED
 #define SkCodecPriv_DEFINED
 
@@ skipping 13 matching lines @@
     uint8_t zeroAlpha = 0;                      \
     uint8_t maxAlpha = 0xFF;
 
 #define UPDATE_RESULT_ALPHA(alpha)              \
     zeroAlpha |= (alpha);                       \
     maxAlpha  &= (alpha);
 
 #define COMPUTE_RESULT_ALPHA                    \
     SkSwizzler::GetResult(zeroAlpha, maxAlpha);
 
+inline float get_scale_from_sample_size(uint32_t sampleSize) { return 1.0f / (float) sampleSize; }

[scroggo, 2015/10/08 20:16:07]

This change (moving this function here, removing SkCodecTools, and including
SkCodecPriv where you previously included SkCodecTools) seems like it should be
its own change. It doesn't appear to be newly used by anything else here.

That said, I'm not sure it's the right thing to do. Not sure if dm etc should
rely on src/codec. (I think we do rely on other private includes, so it's at
least no worse than we already do.)

[msarett, 2015/10/09 20:03:44]

I'll remove this from the change.

Right now, get_scale_from_sample_size is used in dm and nanobench.  My thought
process was that anything that is used by more than one of dm, nanobench, tools
should go in SkCodecPriv.h but maybe that is wrong.

+
 /*
  * returns a scaled dimension based on the original dimension and the sampleSize
  * NOTE: we round down here for scaled dimension to match the behavior of SkImageDecoder
  */
 inline int get_scaled_dimension(int srcDimension, int sampleSize) {
     if (sampleSize > srcDimension) {
         return 1;
     }
     return srcDimension / sampleSize;
 }
@@ skipping 193 matching lines @@
 #endif
 }
 
 #ifdef SK_PRINT_CODEC_MESSAGES
     #define SkCodecPrintf SkDebugf
 #else
     #define SkCodecPrintf(...)
 #endif
 
 #endif // SkCodecPriv_DEFINED