src/codec/SkSampledCodec.cpp - platform/external/skia - Gitiles

 /*
  * 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"
 #include "SkSampledCodec.h"
 #include "SkSampler.h"
 #include "SkTemplates.h"

 SkSampledCodec::SkSampledCodec(SkCodec* codec)
     : INHERITED(codec)
 {}

 SkISize SkSampledCodec::accountForNativeScaling(int* sampleSizePtr, int* nativeSampleSize) const {
     SkISize preSampledSize = this->codec()->getInfo().dimensions();
     int sampleSize = *sampleSizePtr;
     SkASSERT(sampleSize > 1);

     if (nativeSampleSize) {
         *nativeSampleSize = 1;
     }

     // Only JPEG supports native downsampling.
     if (this->codec()->getEncodedFormat() == SkEncodedImageFormat::kJPEG) {
         // See if libjpeg supports this scale directly
         switch (sampleSize) {
             case 2:
             case 4:
             case 8:
                 // This class does not need to do any sampling.
                 *sampleSizePtr = 1;
                 return this->codec()->getScaledDimensions(get_scale_from_sample_size(sampleSize));
             default:
                 break;
         }

         // Check if sampleSize is a multiple of something libjpeg can support.
         int remainder;
         const int sampleSizes[] = { 8, 4, 2 };
         for (int supportedSampleSize : sampleSizes) {
             int actualSampleSize;
             SkTDivMod(sampleSize, supportedSampleSize, &actualSampleSize, &remainder);
             if (0 == remainder) {
                 float scale = get_scale_from_sample_size(supportedSampleSize);

                 // this->codec() will scale to this size.
                 preSampledSize = this->codec()->getScaledDimensions(scale);

                 // And then this class will sample it.
                 *sampleSizePtr = actualSampleSize;
                 if (nativeSampleSize) {
                     *nativeSampleSize = supportedSampleSize;
                 }
                 break;
             }
         }
     }

     return preSampledSize;
 }

 SkISize SkSampledCodec::onGetSampledDimensions(int sampleSize) const {
     const SkISize size = this->accountForNativeScaling(&sampleSize);
     return SkISize::Make(get_scaled_dimension(size.width(), sampleSize),
                          get_scaled_dimension(size.height(), sampleSize));
 }

 SkCodec::Result SkSampledCodec::onGetAndroidPixels(const SkImageInfo& info, void* pixels,
         size_t rowBytes, const AndroidOptions& options) {
     // Create an Options struct for the codec.
     SkCodec::Options codecOptions;
     codecOptions.fZeroInitialized = options.fZeroInitialized;
     codecOptions.fPremulBehavior = SkTransferFunctionBehavior::kIgnore;

     SkIRect* subset = options.fSubset;
     if (!subset || subset->size() == this->codec()->getInfo().dimensions()) {
         if (this->codec()->dimensionsSupported(info.dimensions())) {
             return this->codec()->getPixels(info, pixels, rowBytes, &codecOptions);
         }

         // If the native codec does not support the requested scale, scale by sampling.
         return this->sampledDecode(info, pixels, rowBytes, options);
     }

     // We are performing a subset decode.
     int sampleSize = options.fSampleSize;
     SkISize scaledSize = this->getSampledDimensions(sampleSize);
     if (!this->codec()->dimensionsSupported(scaledSize)) {
         // If the native codec does not support the requested scale, scale by sampling.
         return this->sampledDecode(info, pixels, rowBytes, options);
     }

     // Calculate the scaled subset bounds.
     int scaledSubsetX = subset->x() / sampleSize;
     int scaledSubsetY = subset->y() / sampleSize;
     int scaledSubsetWidth = info.width();
     int scaledSubsetHeight = info.height();

     const SkImageInfo scaledInfo = info.makeWH(scaledSize.width(), scaledSize.height());

     {
         // Although startScanlineDecode expects the bottom and top to match the
         // SkImageInfo, startIncrementalDecode uses them to determine which rows to
         // decode.
         SkIRect incrementalSubset = SkIRect::MakeXYWH(scaledSubsetX, scaledSubsetY,
                                                       scaledSubsetWidth, scaledSubsetHeight);
         codecOptions.fSubset = &incrementalSubset;
         const SkCodec::Result startResult = this->codec()->startIncrementalDecode(
                 scaledInfo, pixels, rowBytes, &codecOptions);
         if (SkCodec::kSuccess == startResult) {
             int rowsDecoded;
             const SkCodec::Result incResult = this->codec()->incrementalDecode(&rowsDecoded);
             if (incResult == SkCodec::kSuccess) {
                 return SkCodec::kSuccess;
             }
             SkASSERT(SkCodec::kIncompleteInput == incResult);

             // FIXME: Can zero initialized be read from SkCodec::fOptions?
             this->codec()->fillIncompleteImage(scaledInfo, pixels, rowBytes,
                     options.fZeroInitialized, scaledSubsetHeight, rowsDecoded);
             return SkCodec::kIncompleteInput;
         } else if (startResult != SkCodec::kUnimplemented) {
             return startResult;
         }
         // Otherwise fall down to use the old scanline decoder.
         // codecOptions.fSubset will be reset below, so it will not continue to
         // point to the object that is no longer on the stack.
     }

     // Start the scanline decode.
     SkIRect scanlineSubset = SkIRect::MakeXYWH(scaledSubsetX, 0, scaledSubsetWidth,
             scaledSize.height());
     codecOptions.fSubset = &scanlineSubset;

     SkCodec::Result result = this->codec()->startScanlineDecode(scaledInfo,
             &codecOptions);
     if (SkCodec::kSuccess != result) {
         return result;
     }

     // At this point, we are only concerned with subsetting.  Either no scale was
     // requested, or the this->codec() is handling the scale.
     // Note that subsetting is only supported for kTopDown, so this code will not be
     // reached for other orders.
     SkASSERT(this->codec()->getScanlineOrder() == SkCodec::kTopDown_SkScanlineOrder);
     if (!this->codec()->skipScanlines(scaledSubsetY)) {
         this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
                 scaledSubsetHeight, 0);
         return SkCodec::kIncompleteInput;
     }

     int decodedLines = this->codec()->getScanlines(pixels, scaledSubsetHeight, rowBytes);
     if (decodedLines != scaledSubsetHeight) {
         return SkCodec::kIncompleteInput;
     }
     return SkCodec::kSuccess;
 }


 SkCodec::Result SkSampledCodec::sampledDecode(const SkImageInfo& info, void* pixels,
         size_t rowBytes, const AndroidOptions& options) {
     // We should only call this function when sampling.
     SkASSERT(options.fSampleSize > 1);

     // Create options struct for the codec.
     SkCodec::Options sampledOptions;
     sampledOptions.fZeroInitialized = options.fZeroInitialized;
     sampledOptions.fPremulBehavior = SkTransferFunctionBehavior::kIgnore;

     // FIXME: This was already called by onGetAndroidPixels. Can we reduce that?
     int sampleSize = options.fSampleSize;
     int nativeSampleSize;
     SkISize nativeSize = this->accountForNativeScaling(&sampleSize, &nativeSampleSize);

     // Check if there is a subset.
     SkIRect subset;
     int subsetY = 0;
     int subsetWidth = nativeSize.width();
     int subsetHeight = nativeSize.height();
     if (options.fSubset) {
         // We will need to know about subsetting in the y-dimension in order to use the
         // scanline decoder.
         // Update the subset to account for scaling done by this->codec().
         const SkIRect* subsetPtr = options.fSubset;

         // Do the divide ourselves, instead of calling get_scaled_dimension. If
         // X and Y are 0, they should remain 0, rather than being upgraded to 1
         // due to being smaller than the sampleSize.
         const int subsetX = subsetPtr->x() / nativeSampleSize;
         subsetY = subsetPtr->y() / nativeSampleSize;

         subsetWidth = get_scaled_dimension(subsetPtr->width(), nativeSampleSize);
         subsetHeight = get_scaled_dimension(subsetPtr->height(), nativeSampleSize);

         // The scanline decoder only needs to be aware of subsetting in the x-dimension.
         subset.setXYWH(subsetX, 0, subsetWidth, nativeSize.height());
         sampledOptions.fSubset = &subset;
     }

     // Since we guarantee that output dimensions are always at least one (even if the sampleSize
     // is greater than a given dimension), the input sampleSize is not always the sampleSize that
     // we use in practice.
     const int sampleX = subsetWidth / info.width();
     const int sampleY = subsetHeight / info.height();

     const int samplingOffsetY = get_start_coord(sampleY);
     const int startY = samplingOffsetY + subsetY;
     const int dstHeight = info.height();

     const SkImageInfo nativeInfo = info.makeWH(nativeSize.width(), nativeSize.height());

     {
         // Although startScanlineDecode expects the bottom and top to match the
         // SkImageInfo, startIncrementalDecode uses them to determine which rows to
         // decode.
         SkCodec::Options incrementalOptions = sampledOptions;
         SkIRect incrementalSubset;
         if (sampledOptions.fSubset) {
             incrementalSubset.fTop = subsetY;
             incrementalSubset.fBottom = subsetY + subsetHeight;
             incrementalSubset.fLeft = sampledOptions.fSubset->fLeft;
             incrementalSubset.fRight = sampledOptions.fSubset->fRight;
             incrementalOptions.fSubset = &incrementalSubset;
         }
         const SkCodec::Result startResult = this->codec()->startIncrementalDecode(nativeInfo,
                 pixels, rowBytes, &incrementalOptions);
         if (SkCodec::kSuccess == startResult) {
             SkSampler* sampler = this->codec()->getSampler(true);
             if (!sampler) {
                 return SkCodec::kUnimplemented;
             }

             if (sampler->setSampleX(sampleX) != info.width()) {
                 return SkCodec::kInvalidScale;
             }
             if (get_scaled_dimension(subsetHeight, sampleY) != info.height()) {
                 return SkCodec::kInvalidScale;
             }

             sampler->setSampleY(sampleY);

             int rowsDecoded;
             const SkCodec::Result incResult = this->codec()->incrementalDecode(&rowsDecoded);
             if (incResult == SkCodec::kSuccess) {
                 return SkCodec::kSuccess;
             }
             SkASSERT(incResult == SkCodec::kIncompleteInput || incResult == SkCodec::kErrorInInput);

             SkASSERT(rowsDecoded <= info.height());
             this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
                                                info.height(), rowsDecoded);
             return incResult;
         } 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);
     if (SkCodec::kSuccess != result) {
         return result;
     }

     SkSampler* sampler = this->codec()->getSampler(true);
     if (!sampler) {
         return SkCodec::kUnimplemented;
     }

     if (sampler->setSampleX(sampleX) != info.width()) {
         return SkCodec::kInvalidScale;
     }
     if (get_scaled_dimension(subsetHeight, sampleY) != info.height()) {
         return SkCodec::kInvalidScale;
     }

     switch(this->codec()->getScanlineOrder()) {
         case SkCodec::kTopDown_SkScanlineOrder: {
             if (!this->codec()->skipScanlines(startY)) {
                 this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
                         dstHeight, 0);
                 return SkCodec::kIncompleteInput;
             }
             void* pixelPtr = pixels;
             for (int y = 0; y < dstHeight; y++) {
                 if (1 != this->codec()->getScanlines(pixelPtr, 1, rowBytes)) {
                     this->codec()->fillIncompleteImage(info, pixels, rowBytes,
                             options.fZeroInitialized, dstHeight, y + 1);
                     return SkCodec::kIncompleteInput;
                 }
                 if (y < dstHeight - 1) {
                     if (!this->codec()->skipScanlines(sampleY - 1)) {
                         this->codec()->fillIncompleteImage(info, pixels, rowBytes,
                                 options.fZeroInitialized, dstHeight, y + 1);
                         return SkCodec::kIncompleteInput;
                     }
                 }
                 pixelPtr = SkTAddOffset<void>(pixelPtr, rowBytes);
             }
             return SkCodec::kSuccess;
         }
         case SkCodec::kBottomUp_SkScanlineOrder: {
             // Note that these modes do not support subsetting.
             SkASSERT(0 == subsetY && nativeSize.height() == subsetHeight);
             int y;
             for (y = 0; y < nativeSize.height(); y++) {
                 int srcY = this->codec()->nextScanline();
                 if (is_coord_necessary(srcY, sampleY, dstHeight)) {
                     void* pixelPtr = SkTAddOffset<void>(pixels,
                             rowBytes * get_dst_coord(srcY, sampleY));
                     if (1 != this->codec()->getScanlines(pixelPtr, 1, rowBytes)) {
                         break;
                     }
                 } else {
                     if (!this->codec()->skipScanlines(1)) {
                         break;
                     }
                 }
             }

             if (nativeSize.height() == y) {
                 return SkCodec::kSuccess;
             }

             // We handle filling uninitialized memory here instead of using this->codec().
             // this->codec() does not know that we are sampling.
             const uint64_t fillValue = this->codec()->getFillValue(info);
             const SkImageInfo fillInfo = info.makeWH(info.width(), 1);
             for (; y < nativeSize.height(); y++) {
                 int srcY = this->codec()->outputScanline(y);
                 if (!is_coord_necessary(srcY, sampleY, dstHeight)) {
                     continue;
                 }

                 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;
     }
 }
	/*
	* 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"
	#include "SkSampledCodec.h"
	#include "SkSampler.h"
	#include "SkTemplates.h"

	SkSampledCodec::SkSampledCodec(SkCodec* codec)
	: INHERITED(codec)
	{}

	SkISize SkSampledCodec::accountForNativeScaling(int* sampleSizePtr, int* nativeSampleSize) const {
	SkISize preSampledSize = this->codec()->getInfo().dimensions();
	int sampleSize = *sampleSizePtr;
	SkASSERT(sampleSize > 1);

	if (nativeSampleSize) {
	*nativeSampleSize = 1;
	}

	// Only JPEG supports native downsampling.
	if (this->codec()->getEncodedFormat() == SkEncodedImageFormat::kJPEG) {
	// See if libjpeg supports this scale directly
	switch (sampleSize) {
	case 2:
	case 4:
	case 8:
	// This class does not need to do any sampling.
	*sampleSizePtr = 1;
	return this->codec()->getScaledDimensions(get_scale_from_sample_size(sampleSize));
	default:
	break;
	}

	// Check if sampleSize is a multiple of something libjpeg can support.
	int remainder;
	const int sampleSizes[] = { 8, 4, 2 };
	for (int supportedSampleSize : sampleSizes) {
	int actualSampleSize;
	SkTDivMod(sampleSize, supportedSampleSize, &actualSampleSize, &remainder);
	if (0 == remainder) {
	float scale = get_scale_from_sample_size(supportedSampleSize);

	// this->codec() will scale to this size.
	preSampledSize = this->codec()->getScaledDimensions(scale);

	// And then this class will sample it.
	*sampleSizePtr = actualSampleSize;
	if (nativeSampleSize) {
	*nativeSampleSize = supportedSampleSize;
	}
	break;
	}
	}
	}

	return preSampledSize;
	}

	SkISize SkSampledCodec::onGetSampledDimensions(int sampleSize) const {
	const SkISize size = this->accountForNativeScaling(&sampleSize);
	return SkISize::Make(get_scaled_dimension(size.width(), sampleSize),
	get_scaled_dimension(size.height(), sampleSize));
	}

	SkCodec::Result SkSampledCodec::onGetAndroidPixels(const SkImageInfo& info, void* pixels,
	size_t rowBytes, const AndroidOptions& options) {
	// Create an Options struct for the codec.
	SkCodec::Options codecOptions;
	codecOptions.fZeroInitialized = options.fZeroInitialized;
	codecOptions.fPremulBehavior = SkTransferFunctionBehavior::kIgnore;

	SkIRect* subset = options.fSubset;
	if (!subset \|\| subset->size() == this->codec()->getInfo().dimensions()) {
	if (this->codec()->dimensionsSupported(info.dimensions())) {
	return this->codec()->getPixels(info, pixels, rowBytes, &codecOptions);
	}

	// If the native codec does not support the requested scale, scale by sampling.
	return this->sampledDecode(info, pixels, rowBytes, options);
	}

	// We are performing a subset decode.
	int sampleSize = options.fSampleSize;
	SkISize scaledSize = this->getSampledDimensions(sampleSize);
	if (!this->codec()->dimensionsSupported(scaledSize)) {
	// If the native codec does not support the requested scale, scale by sampling.
	return this->sampledDecode(info, pixels, rowBytes, options);
	}

	// Calculate the scaled subset bounds.
	int scaledSubsetX = subset->x() / sampleSize;
	int scaledSubsetY = subset->y() / sampleSize;
	int scaledSubsetWidth = info.width();
	int scaledSubsetHeight = info.height();

	const SkImageInfo scaledInfo = info.makeWH(scaledSize.width(), scaledSize.height());

	{
	// Although startScanlineDecode expects the bottom and top to match the
	// SkImageInfo, startIncrementalDecode uses them to determine which rows to
	// decode.
	SkIRect incrementalSubset = SkIRect::MakeXYWH(scaledSubsetX, scaledSubsetY,
	scaledSubsetWidth, scaledSubsetHeight);
	codecOptions.fSubset = &incrementalSubset;
	const SkCodec::Result startResult = this->codec()->startIncrementalDecode(
	scaledInfo, pixels, rowBytes, &codecOptions);
	if (SkCodec::kSuccess == startResult) {
	int rowsDecoded;
	const SkCodec::Result incResult = this->codec()->incrementalDecode(&rowsDecoded);
	if (incResult == SkCodec::kSuccess) {
	return SkCodec::kSuccess;
	}
	SkASSERT(SkCodec::kIncompleteInput == incResult);

	// FIXME: Can zero initialized be read from SkCodec::fOptions?
	this->codec()->fillIncompleteImage(scaledInfo, pixels, rowBytes,
	options.fZeroInitialized, scaledSubsetHeight, rowsDecoded);
	return SkCodec::kIncompleteInput;
	} else if (startResult != SkCodec::kUnimplemented) {
	return startResult;
	}
	// Otherwise fall down to use the old scanline decoder.
	// codecOptions.fSubset will be reset below, so it will not continue to
	// point to the object that is no longer on the stack.
	}

	// Start the scanline decode.
	SkIRect scanlineSubset = SkIRect::MakeXYWH(scaledSubsetX, 0, scaledSubsetWidth,
	scaledSize.height());
	codecOptions.fSubset = &scanlineSubset;

	SkCodec::Result result = this->codec()->startScanlineDecode(scaledInfo,
	&codecOptions);
	if (SkCodec::kSuccess != result) {
	return result;
	}

	// At this point, we are only concerned with subsetting. Either no scale was
	// requested, or the this->codec() is handling the scale.
	// Note that subsetting is only supported for kTopDown, so this code will not be
	// reached for other orders.
	SkASSERT(this->codec()->getScanlineOrder() == SkCodec::kTopDown_SkScanlineOrder);
	if (!this->codec()->skipScanlines(scaledSubsetY)) {
	this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
	scaledSubsetHeight, 0);
	return SkCodec::kIncompleteInput;
	}

	int decodedLines = this->codec()->getScanlines(pixels, scaledSubsetHeight, rowBytes);
	if (decodedLines != scaledSubsetHeight) {
	return SkCodec::kIncompleteInput;
	}
	return SkCodec::kSuccess;
	}


	SkCodec::Result SkSampledCodec::sampledDecode(const SkImageInfo& info, void* pixels,
	size_t rowBytes, const AndroidOptions& options) {
	// We should only call this function when sampling.
	SkASSERT(options.fSampleSize > 1);

	// Create options struct for the codec.
	SkCodec::Options sampledOptions;
	sampledOptions.fZeroInitialized = options.fZeroInitialized;
	sampledOptions.fPremulBehavior = SkTransferFunctionBehavior::kIgnore;

	// FIXME: This was already called by onGetAndroidPixels. Can we reduce that?
	int sampleSize = options.fSampleSize;
	int nativeSampleSize;
	SkISize nativeSize = this->accountForNativeScaling(&sampleSize, &nativeSampleSize);

	// Check if there is a subset.
	SkIRect subset;
	int subsetY = 0;
	int subsetWidth = nativeSize.width();
	int subsetHeight = nativeSize.height();
	if (options.fSubset) {
	// We will need to know about subsetting in the y-dimension in order to use the
	// scanline decoder.
	// Update the subset to account for scaling done by this->codec().
	const SkIRect* subsetPtr = options.fSubset;

	// Do the divide ourselves, instead of calling get_scaled_dimension. If
	// X and Y are 0, they should remain 0, rather than being upgraded to 1
	// due to being smaller than the sampleSize.
	const int subsetX = subsetPtr->x() / nativeSampleSize;
	subsetY = subsetPtr->y() / nativeSampleSize;

	subsetWidth = get_scaled_dimension(subsetPtr->width(), nativeSampleSize);
	subsetHeight = get_scaled_dimension(subsetPtr->height(), nativeSampleSize);

	// The scanline decoder only needs to be aware of subsetting in the x-dimension.
	subset.setXYWH(subsetX, 0, subsetWidth, nativeSize.height());
	sampledOptions.fSubset = &subset;
	}

	// Since we guarantee that output dimensions are always at least one (even if the sampleSize
	// is greater than a given dimension), the input sampleSize is not always the sampleSize that
	// we use in practice.
	const int sampleX = subsetWidth / info.width();
	const int sampleY = subsetHeight / info.height();

	const int samplingOffsetY = get_start_coord(sampleY);
	const int startY = samplingOffsetY + subsetY;
	const int dstHeight = info.height();

	const SkImageInfo nativeInfo = info.makeWH(nativeSize.width(), nativeSize.height());

	{
	// Although startScanlineDecode expects the bottom and top to match the
	// SkImageInfo, startIncrementalDecode uses them to determine which rows to
	// decode.
	SkCodec::Options incrementalOptions = sampledOptions;
	SkIRect incrementalSubset;
	if (sampledOptions.fSubset) {
	incrementalSubset.fTop = subsetY;
	incrementalSubset.fBottom = subsetY + subsetHeight;
	incrementalSubset.fLeft = sampledOptions.fSubset->fLeft;
	incrementalSubset.fRight = sampledOptions.fSubset->fRight;
	incrementalOptions.fSubset = &incrementalSubset;
	}
	const SkCodec::Result startResult = this->codec()->startIncrementalDecode(nativeInfo,
	pixels, rowBytes, &incrementalOptions);
	if (SkCodec::kSuccess == startResult) {
	SkSampler* sampler = this->codec()->getSampler(true);
	if (!sampler) {
	return SkCodec::kUnimplemented;
	}

	if (sampler->setSampleX(sampleX) != info.width()) {
	return SkCodec::kInvalidScale;
	}
	if (get_scaled_dimension(subsetHeight, sampleY) != info.height()) {
	return SkCodec::kInvalidScale;
	}

	sampler->setSampleY(sampleY);

	int rowsDecoded;
	const SkCodec::Result incResult = this->codec()->incrementalDecode(&rowsDecoded);
	if (incResult == SkCodec::kSuccess) {
	return SkCodec::kSuccess;
	}
	SkASSERT(incResult == SkCodec::kIncompleteInput \|\| incResult == SkCodec::kErrorInInput);

	SkASSERT(rowsDecoded <= info.height());
	this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
	info.height(), rowsDecoded);
	return incResult;
	} 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);
	if (SkCodec::kSuccess != result) {
	return result;
	}

	SkSampler* sampler = this->codec()->getSampler(true);
	if (!sampler) {
	return SkCodec::kUnimplemented;
	}

	if (sampler->setSampleX(sampleX) != info.width()) {
	return SkCodec::kInvalidScale;
	}
	if (get_scaled_dimension(subsetHeight, sampleY) != info.height()) {
	return SkCodec::kInvalidScale;
	}

	switch(this->codec()->getScanlineOrder()) {
	case SkCodec::kTopDown_SkScanlineOrder: {
	if (!this->codec()->skipScanlines(startY)) {
	this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
	dstHeight, 0);
	return SkCodec::kIncompleteInput;
	}
	void* pixelPtr = pixels;
	for (int y = 0; y < dstHeight; y++) {
	if (1 != this->codec()->getScanlines(pixelPtr, 1, rowBytes)) {
	this->codec()->fillIncompleteImage(info, pixels, rowBytes,
	options.fZeroInitialized, dstHeight, y + 1);
	return SkCodec::kIncompleteInput;
	}
	if (y < dstHeight - 1) {
	if (!this->codec()->skipScanlines(sampleY - 1)) {
	this->codec()->fillIncompleteImage(info, pixels, rowBytes,
	options.fZeroInitialized, dstHeight, y + 1);
	return SkCodec::kIncompleteInput;
	}
	}
	pixelPtr = SkTAddOffset<void>(pixelPtr, rowBytes);
	}
	return SkCodec::kSuccess;
	}
	case SkCodec::kBottomUp_SkScanlineOrder: {
	// Note that these modes do not support subsetting.
	SkASSERT(0 == subsetY && nativeSize.height() == subsetHeight);
	int y;
	for (y = 0; y < nativeSize.height(); y++) {
	int srcY = this->codec()->nextScanline();
	if (is_coord_necessary(srcY, sampleY, dstHeight)) {
	void* pixelPtr = SkTAddOffset<void>(pixels,
	rowBytes * get_dst_coord(srcY, sampleY));
	if (1 != this->codec()->getScanlines(pixelPtr, 1, rowBytes)) {
	break;
	}
	} else {
	if (!this->codec()->skipScanlines(1)) {
	break;
	}
	}
	}

	if (nativeSize.height() == y) {
	return SkCodec::kSuccess;
	}

	// We handle filling uninitialized memory here instead of using this->codec().
	// this->codec() does not know that we are sampling.
	const uint64_t fillValue = this->codec()->getFillValue(info);
	const SkImageInfo fillInfo = info.makeWH(info.width(), 1);
	for (; y < nativeSize.height(); y++) {
	int srcY = this->codec()->outputScanline(y);
	if (!is_coord_necessary(srcY, sampleY, dstHeight)) {
	continue;
	}

	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;
	}
	}