Fix filling of incomplete images in SkSampledCodec

src/codec/SkSampledCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec.h"
 #include "SkCodecPriv.h"
 #include "SkMath.h"
@@ skipping 239 matching lines @@
             }
 
             sampler->setSampleY(sampleY);
 
             int rowsDecoded;
             const SkCodec::Result incResult = this->codec()->incrementalDecode(&rowsDecoded);
             if (incResult == SkCodec::kSuccess) {
                 return SkCodec::kSuccess;
             }
             SkASSERT(incResult == SkCodec::kIncompleteInput);
-            const int lastRowInOutput = (rowsDecoded - startY) / sampleY;
-            // FIXME: Should this be info or nativeInfo? Does it make a difference?
+
+            // Count the rows that we decoded, and also did not skip.
+            const int trueRowsDecoded = (rowsDecoded + sampleY - 1) / sampleY;
             this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
-                                               info.height(), lastRowInOutput);
+                                               info.height(), trueRowsDecoded);
             return SkCodec::kIncompleteInput;
         } else if (startResult != SkCodec::kUnimplemented) {
             return startResult;
         } // kUnimplemented means use the old method.
     }
 
     // Start the scanline decode.
     SkCodec::Result result = this->codec()->startScanlineDecode(nativeInfo,
             &sampledOptions, options.fColorPtr, options.fColorCount);
     if (SkCodec::kSuccess != result) {
@@ skipping 74 matching lines @@
                 void* rowPtr = SkTAddOffset<void>(pixels, rowBytes * get_dst_coord(srcY, sampleY));
                 SkSampler::Fill(fillInfo, rowPtr, rowBytes, fillValue, options.fZeroInitialized);
             }
             return SkCodec::kIncompleteInput;
         }
         default:
             SkASSERT(false);
             return SkCodec::kUnimplemented;
     }
 }