src/codec/SkWebpCodec.cpp - skia - Git at Google

 /*
  * 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 "SkCodecPriv.h"
 #include "SkColorSpaceXform.h"
 #include "SkWebpCodec.h"
 #include "SkStreamPriv.h"
 #include "SkTemplates.h"

 // A WebP decoder on top of (subset of) libwebp
 // For more information on WebP image format, and libwebp library, see:
 //   https://code.google.com/speed/webp/
 //   http://www.webmproject.org/code/#libwebp-webp-image-library
 //   https://chromium.googlesource.com/webm/libwebp

 // If moving libwebp out of skia source tree, path for webp headers must be
 // updated accordingly. Here, we enforce using local copy in webp sub-directory.
 #include "webp/decode.h"
 #include "webp/demux.h"
 #include "webp/encode.h"

 bool SkWebpCodec::IsWebp(const void* buf, size_t bytesRead) {
     // WEBP starts with the following:
     // RIFFXXXXWEBPVP
     // Where XXXX is unspecified.
     const char* bytes = static_cast<const char*>(buf);
     return bytesRead >= 14 && !memcmp(bytes, "RIFF", 4) && !memcmp(&bytes[8], "WEBPVP", 6);
 }

 // Parse headers of RIFF container, and check for valid Webp (VP8) content.
 // NOTE: This calls peek instead of read, since onGetPixels will need these
 // bytes again.
 // Returns an SkWebpCodec on success;
 SkCodec* SkWebpCodec::NewFromStream(SkStream* stream) {
     SkAutoTDelete<SkStream> streamDeleter(stream);

     // Webp demux needs a contiguous data buffer.
     sk_sp<SkData> data = nullptr;
     if (stream->getMemoryBase()) {
         // It is safe to make without copy because we'll hold onto the stream.
         data = SkData::MakeWithoutCopy(stream->getMemoryBase(), stream->getLength());
     } else {
         data = SkCopyStreamToData(stream);

         // If we are forced to copy the stream to a data, we can go ahead and delete the stream.
         streamDeleter.reset(nullptr);
     }

     // It's a little strange that the |demux| will outlive |webpData|, though it needs the
     // pointer in |webpData| to remain valid.  This works because the pointer remains valid
     // until the SkData is freed.
     WebPData webpData = { data->bytes(), data->size() };
     SkAutoTCallVProc<WebPDemuxer, WebPDemuxDelete> demux(WebPDemuxPartial(&webpData, nullptr));
     if (nullptr == demux) {
         return nullptr;
     }

     WebPChunkIterator chunkIterator;
     SkAutoTCallVProc<WebPChunkIterator, WebPDemuxReleaseChunkIterator> autoCI(&chunkIterator);
     sk_sp<SkColorSpace> colorSpace = nullptr;
     if (WebPDemuxGetChunk(demux, "ICCP", 1, &chunkIterator)) {
         colorSpace = SkColorSpace::NewICC(chunkIterator.chunk.bytes, chunkIterator.chunk.size);
     }

     if (!colorSpace) {
         colorSpace = SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
     }

     // Since we do not yet support animation, we get the |width|, |height|, |color|, and |alpha|
     // from the first frame.  It's the only frame we will decode.
     //
     // TODO:
     // When we support animation, we'll want to report the canvas width and canvas height instead.
     // We can get these from the |demux| directly.
     // What |color| and |alpha| will we want to report though?  WebP allows different frames
     // to be encoded in different ways, making the encoded format difficult to describe.
     WebPIterator frame;
     SkAutoTCallVProc<WebPIterator, WebPDemuxReleaseIterator> autoFrame(&frame);
     if (!WebPDemuxGetFrame(demux, 1, &frame)) {
         return nullptr;
     }

     // Sanity check for image size that's about to be decoded.
     {
         const int64_t size = sk_64_mul(frame.width, frame.height);
         if (!sk_64_isS32(size)) {
             return nullptr;
         }
         // now check that if we are 4-bytes per pixel, we also don't overflow
         if (sk_64_asS32(size) > (0x7FFFFFFF >> 2)) {
             return nullptr;
         }
     }

     // TODO:
     // The only reason we actually need to call WebPGetFeatures() is to get the |features.format|.
     // This call actually re-reads the frame header.  Should we suggest that libwebp expose
     // the format on the |frame|?
     WebPBitstreamFeatures features;
     VP8StatusCode status = WebPGetFeatures(frame.fragment.bytes, frame.fragment.size, &features);
     if (VP8_STATUS_OK != status) {
         return nullptr;
     }

     SkEncodedInfo::Color color;
     SkEncodedInfo::Alpha alpha;
     switch (features.format) {
         case 0:
             // This indicates a "mixed" format.  We would see this for
             // animated webps or for webps encoded in multiple fragments.
             // I believe that this is a rare case.
             // We could also guess kYUV here, but I think it makes more
             // sense to guess kBGRA which is likely closer to the final
             // output.  Otherwise, we might end up converting
             // BGRA->YUVA->BGRA.
             color = SkEncodedInfo::kBGRA_Color;
             alpha = SkEncodedInfo::kUnpremul_Alpha;
             break;
         case 1:
             // This is the lossy format (YUV).
             if (SkToBool(features.has_alpha)) {
                 color = SkEncodedInfo::kYUVA_Color;
                 alpha = SkEncodedInfo::kUnpremul_Alpha;
             } else {
                 color = SkEncodedInfo::kYUV_Color;
                 alpha = SkEncodedInfo::kOpaque_Alpha;
             }
             break;
         case 2:
             // This is the lossless format (BGRA).
             color = SkEncodedInfo::kBGRA_Color;
             alpha = SkEncodedInfo::kUnpremul_Alpha;
             break;
         default:
             return nullptr;
     }

     SkEncodedInfo info = SkEncodedInfo::Make(color, alpha, 8);
     return new SkWebpCodec(features.width, features.height, info, std::move(colorSpace),
                            streamDeleter.release(), demux.release(), std::move(data));
 }

 SkISize SkWebpCodec::onGetScaledDimensions(float desiredScale) const {
     SkISize dim = this->getInfo().dimensions();
     // SkCodec treats zero dimensional images as errors, so the minimum size
     // that we will recommend is 1x1.
     dim.fWidth = SkTMax(1, SkScalarRoundToInt(desiredScale * dim.fWidth));
     dim.fHeight = SkTMax(1, SkScalarRoundToInt(desiredScale * dim.fHeight));
     return dim;
 }

 bool SkWebpCodec::onDimensionsSupported(const SkISize& dim) {
     const SkImageInfo& info = this->getInfo();
     return dim.width() >= 1 && dim.width() <= info.width()
             && dim.height() >= 1 && dim.height() <= info.height();
 }

 static WEBP_CSP_MODE webp_decode_mode(SkColorType ct, bool premultiply) {
     switch (ct) {
         case kBGRA_8888_SkColorType:
             return premultiply ? MODE_bgrA : MODE_BGRA;
         case kRGBA_8888_SkColorType:
             return premultiply ? MODE_rgbA : MODE_RGBA;
         case kRGB_565_SkColorType:
             return MODE_RGB_565;
         default:
             return MODE_LAST;
     }
 }

 bool SkWebpCodec::onGetValidSubset(SkIRect* desiredSubset) const {
     if (!desiredSubset) {
         return false;
     }

     SkIRect dimensions  = SkIRect::MakeSize(this->getInfo().dimensions());
     if (!dimensions.contains(*desiredSubset)) {
         return false;
     }

     // As stated below, libwebp snaps to even left and top. Make sure top and left are even, so we
     // decode this exact subset.
     // Leave right and bottom unmodified, so we suggest a slightly larger subset than requested.
     desiredSubset->fLeft = (desiredSubset->fLeft >> 1) << 1;
     desiredSubset->fTop = (desiredSubset->fTop >> 1) << 1;
     return true;
 }

 SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
                                          const Options& options, SkPMColor*, int*,
                                          int* rowsDecodedPtr) {
     if (!conversion_possible(dstInfo, this->getInfo())) {
         return kInvalidConversion;
     }

     std::unique_ptr<SkColorSpaceXform> colorXform = nullptr;
     if (needs_color_xform(dstInfo, this->getInfo())) {
         colorXform = SkColorSpaceXform::New(sk_ref_sp(this->getInfo().colorSpace()),
                                             sk_ref_sp(dstInfo.colorSpace()));
         SkASSERT(colorXform);
     }

     WebPDecoderConfig config;
     if (0 == WebPInitDecoderConfig(&config)) {
         // ABI mismatch.
         // FIXME: New enum for this?
         return kInvalidInput;
     }

     // Free any memory associated with the buffer. Must be called last, so we declare it first.
     SkAutoTCallVProc<WebPDecBuffer, WebPFreeDecBuffer> autoFree(&(config.output));

     SkIRect bounds = SkIRect::MakeSize(this->getInfo().dimensions());
     if (options.fSubset) {
         // Caller is requesting a subset.
         if (!bounds.contains(*options.fSubset)) {
             // The subset is out of bounds.
             return kInvalidParameters;
         }

         bounds = *options.fSubset;

         // This is tricky. libwebp snaps the top and left to even values. We could let libwebp
         // do the snap, and return a subset which is a different one than requested. The problem
         // with that approach is that the caller may try to stitch subsets together, and if we
         // returned different subsets than requested, there would be artifacts at the boundaries.
         // Instead, we report that we cannot support odd values for top and left..
         if (!SkIsAlign2(bounds.fLeft) || !SkIsAlign2(bounds.fTop)) {
             return kInvalidParameters;
         }

 #ifdef SK_DEBUG
         {
             // Make a copy, since getValidSubset can change its input.
             SkIRect subset(bounds);
             // That said, getValidSubset should *not* change its input, in this case; otherwise
             // getValidSubset does not match the actual subsets we can do.
             SkASSERT(this->getValidSubset(&subset) && subset == bounds);
         }
 #endif

         config.options.use_cropping = 1;
         config.options.crop_left = bounds.fLeft;
         config.options.crop_top = bounds.fTop;
         config.options.crop_width = bounds.width();
         config.options.crop_height = bounds.height();
     }

     SkISize dstDimensions = dstInfo.dimensions();
     if (bounds.size() != dstDimensions) {
         // Caller is requesting scaling.
         config.options.use_scaling = 1;
         config.options.scaled_width = dstDimensions.width();
         config.options.scaled_height = dstDimensions.height();
     }

     // FIXME (msarett):
     // Lossless webp is encoded as BGRA.  In that case, it would be more efficient to
     // to decode BGRA and apply the color xform to a BGRA buffer.
     config.output.colorspace = colorXform ? MODE_RGBA :
             webp_decode_mode(dstInfo.colorType(), dstInfo.alphaType() == kPremul_SkAlphaType);
     config.output.is_external_memory = 1;

     // We will decode the entire image and then perform the color transform.  libwebp
     // does not provide a row-by-row API.  This is a shame particularly in the F16 case,
     // where we need to allocate an extra image-sized buffer.
     SkAutoTMalloc<uint32_t> pixels;
     if (kRGBA_F16_SkColorType == dstInfo.colorType()) {
         pixels.reset(dstDimensions.width() * dstDimensions.height());
         config.output.u.RGBA.rgba = (uint8_t*) pixels.get();
         config.output.u.RGBA.stride = (int) dstDimensions.width() * sizeof(uint32_t);
         config.output.u.RGBA.size = config.output.u.RGBA.stride * dstDimensions.height();
     } else {
         config.output.u.RGBA.rgba = (uint8_t*) dst;
         config.output.u.RGBA.stride = (int) rowBytes;
         config.output.u.RGBA.size = dstInfo.getSafeSize(rowBytes);
     }

     WebPIterator frame;
     SkAutoTCallVProc<WebPIterator, WebPDemuxReleaseIterator> autoFrame(&frame);
     // If this succeeded in NewFromStream(), it should succeed again here.
     SkAssertResult(WebPDemuxGetFrame(fDemux, 1, &frame));

     SkAutoTCallVProc<WebPIDecoder, WebPIDelete> idec(WebPIDecode(nullptr, 0, &config));
     if (!idec) {
         return kInvalidInput;
     }

     int rowsDecoded;
     SkCodec::Result result;
     switch (WebPIUpdate(idec, frame.fragment.bytes, frame.fragment.size)) {
         case VP8_STATUS_OK:
             rowsDecoded = dstInfo.height();
             result = kSuccess;
             break;
         case VP8_STATUS_SUSPENDED:
             WebPIDecGetRGB(idec, rowsDecodedPtr, nullptr, nullptr, nullptr);
             rowsDecoded = *rowsDecodedPtr;
             result = kIncompleteInput;
             break;
         default:
             return kInvalidInput;
     }

     if (colorXform) {
         SkColorSpaceXform::ColorFormat colorFormat = select_xform_format(dstInfo.colorType());
         SkAlphaType xformAlphaType = select_xform_alpha(dstInfo.alphaType(),
                                                         this->getInfo().alphaType());

         uint32_t* src = (uint32_t*) config.output.u.RGBA.rgba;
         size_t srcRowBytes = config.output.u.RGBA.stride;
         for (int y = 0; y < rowsDecoded; y++) {
             colorXform->apply(dst, src, dstInfo.width(), colorFormat, xformAlphaType);
             dst = SkTAddOffset<void>(dst, rowBytes);
             src = SkTAddOffset<uint32_t>(src, srcRowBytes);
         }
     }

     return result;
 }

 SkWebpCodec::SkWebpCodec(int width, int height, const SkEncodedInfo& info,
                          sk_sp<SkColorSpace> colorSpace, SkStream* stream, WebPDemuxer* demux,
                          sk_sp<SkData> data)
     : INHERITED(width, height, info, stream, std::move(colorSpace))
     , fDemux(demux)
     , fData(std::move(data))
 {}
	/*
	* 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 "SkCodecPriv.h"
	#include "SkColorSpaceXform.h"
	#include "SkWebpCodec.h"
	#include "SkStreamPriv.h"
	#include "SkTemplates.h"

	// A WebP decoder on top of (subset of) libwebp
	// For more information on WebP image format, and libwebp library, see:
	// https://code.google.com/speed/webp/
	// http://www.webmproject.org/code/#libwebp-webp-image-library
	// https://chromium.googlesource.com/webm/libwebp

	// If moving libwebp out of skia source tree, path for webp headers must be
	// updated accordingly. Here, we enforce using local copy in webp sub-directory.
	#include "webp/decode.h"
	#include "webp/demux.h"
	#include "webp/encode.h"

	bool SkWebpCodec::IsWebp(const void* buf, size_t bytesRead) {
	// WEBP starts with the following:
	// RIFFXXXXWEBPVP
	// Where XXXX is unspecified.
	const char* bytes = static_cast<const char*>(buf);
	return bytesRead >= 14 && !memcmp(bytes, "RIFF", 4) && !memcmp(&bytes[8], "WEBPVP", 6);
	}

	// Parse headers of RIFF container, and check for valid Webp (VP8) content.
	// NOTE: This calls peek instead of read, since onGetPixels will need these
	// bytes again.
	// Returns an SkWebpCodec on success;
	SkCodec* SkWebpCodec::NewFromStream(SkStream* stream) {
	SkAutoTDelete<SkStream> streamDeleter(stream);

	// Webp demux needs a contiguous data buffer.
	sk_sp<SkData> data = nullptr;
	if (stream->getMemoryBase()) {
	// It is safe to make without copy because we'll hold onto the stream.
	data = SkData::MakeWithoutCopy(stream->getMemoryBase(), stream->getLength());
	} else {
	data = SkCopyStreamToData(stream);

	// If we are forced to copy the stream to a data, we can go ahead and delete the stream.
	streamDeleter.reset(nullptr);
	}

	// It's a little strange that the \|demux\| will outlive \|webpData\|, though it needs the
	// pointer in \|webpData\| to remain valid. This works because the pointer remains valid
	// until the SkData is freed.
	WebPData webpData = { data->bytes(), data->size() };
	SkAutoTCallVProc<WebPDemuxer, WebPDemuxDelete> demux(WebPDemuxPartial(&webpData, nullptr));
	if (nullptr == demux) {
	return nullptr;
	}

	WebPChunkIterator chunkIterator;
	SkAutoTCallVProc<WebPChunkIterator, WebPDemuxReleaseChunkIterator> autoCI(&chunkIterator);
	sk_sp<SkColorSpace> colorSpace = nullptr;
	if (WebPDemuxGetChunk(demux, "ICCP", 1, &chunkIterator)) {
	colorSpace = SkColorSpace::NewICC(chunkIterator.chunk.bytes, chunkIterator.chunk.size);
	}

	if (!colorSpace) {
	colorSpace = SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
	}

	// Since we do not yet support animation, we get the \|width\|, \|height\|, \|color\|, and \|alpha\|
	// from the first frame. It's the only frame we will decode.
	//
	// TODO:
	// When we support animation, we'll want to report the canvas width and canvas height instead.
	// We can get these from the \|demux\| directly.
	// What \|color\| and \|alpha\| will we want to report though? WebP allows different frames
	// to be encoded in different ways, making the encoded format difficult to describe.
	WebPIterator frame;
	SkAutoTCallVProc<WebPIterator, WebPDemuxReleaseIterator> autoFrame(&frame);
	if (!WebPDemuxGetFrame(demux, 1, &frame)) {
	return nullptr;
	}

	// Sanity check for image size that's about to be decoded.
	{
	const int64_t size = sk_64_mul(frame.width, frame.height);
	if (!sk_64_isS32(size)) {
	return nullptr;
	}
	// now check that if we are 4-bytes per pixel, we also don't overflow
	if (sk_64_asS32(size) > (0x7FFFFFFF >> 2)) {
	return nullptr;
	}
	}

	// TODO:
	// The only reason we actually need to call WebPGetFeatures() is to get the \|features.format\|.
	// This call actually re-reads the frame header. Should we suggest that libwebp expose
	// the format on the \|frame\|?
	WebPBitstreamFeatures features;
	VP8StatusCode status = WebPGetFeatures(frame.fragment.bytes, frame.fragment.size, &features);
	if (VP8_STATUS_OK != status) {
	return nullptr;
	}

	SkEncodedInfo::Color color;
	SkEncodedInfo::Alpha alpha;
	switch (features.format) {
	case 0:
	// This indicates a "mixed" format. We would see this for
	// animated webps or for webps encoded in multiple fragments.
	// I believe that this is a rare case.
	// We could also guess kYUV here, but I think it makes more
	// sense to guess kBGRA which is likely closer to the final
	// output. Otherwise, we might end up converting
	// BGRA->YUVA->BGRA.
	color = SkEncodedInfo::kBGRA_Color;
	alpha = SkEncodedInfo::kUnpremul_Alpha;
	break;
	case 1:
	// This is the lossy format (YUV).
	if (SkToBool(features.has_alpha)) {
	color = SkEncodedInfo::kYUVA_Color;
	alpha = SkEncodedInfo::kUnpremul_Alpha;
	} else {
	color = SkEncodedInfo::kYUV_Color;
	alpha = SkEncodedInfo::kOpaque_Alpha;
	}
	break;
	case 2:
	// This is the lossless format (BGRA).
	color = SkEncodedInfo::kBGRA_Color;
	alpha = SkEncodedInfo::kUnpremul_Alpha;
	break;
	default:
	return nullptr;
	}

	SkEncodedInfo info = SkEncodedInfo::Make(color, alpha, 8);
	return new SkWebpCodec(features.width, features.height, info, std::move(colorSpace),
	streamDeleter.release(), demux.release(), std::move(data));
	}

	SkISize SkWebpCodec::onGetScaledDimensions(float desiredScale) const {
	SkISize dim = this->getInfo().dimensions();
	// SkCodec treats zero dimensional images as errors, so the minimum size
	// that we will recommend is 1x1.
	dim.fWidth = SkTMax(1, SkScalarRoundToInt(desiredScale * dim.fWidth));
	dim.fHeight = SkTMax(1, SkScalarRoundToInt(desiredScale * dim.fHeight));
	return dim;
	}

	bool SkWebpCodec::onDimensionsSupported(const SkISize& dim) {
	const SkImageInfo& info = this->getInfo();
	return dim.width() >= 1 && dim.width() <= info.width()
	&& dim.height() >= 1 && dim.height() <= info.height();
	}

	static WEBP_CSP_MODE webp_decode_mode(SkColorType ct, bool premultiply) {
	switch (ct) {
	case kBGRA_8888_SkColorType:
	return premultiply ? MODE_bgrA : MODE_BGRA;
	case kRGBA_8888_SkColorType:
	return premultiply ? MODE_rgbA : MODE_RGBA;
	case kRGB_565_SkColorType:
	return MODE_RGB_565;
	default:
	return MODE_LAST;
	}
	}

	bool SkWebpCodec::onGetValidSubset(SkIRect* desiredSubset) const {
	if (!desiredSubset) {
	return false;
	}

	SkIRect dimensions = SkIRect::MakeSize(this->getInfo().dimensions());
	if (!dimensions.contains(*desiredSubset)) {
	return false;
	}

	// As stated below, libwebp snaps to even left and top. Make sure top and left are even, so we
	// decode this exact subset.
	// Leave right and bottom unmodified, so we suggest a slightly larger subset than requested.
	desiredSubset->fLeft = (desiredSubset->fLeft >> 1) << 1;
	desiredSubset->fTop = (desiredSubset->fTop >> 1) << 1;
	return true;
	}

	SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
	const Options& options, SkPMColor, int,
	int* rowsDecodedPtr) {
	if (!conversion_possible(dstInfo, this->getInfo())) {
	return kInvalidConversion;
	}

	std::unique_ptr<SkColorSpaceXform> colorXform = nullptr;
	if (needs_color_xform(dstInfo, this->getInfo())) {
	colorXform = SkColorSpaceXform::New(sk_ref_sp(this->getInfo().colorSpace()),
	sk_ref_sp(dstInfo.colorSpace()));
	SkASSERT(colorXform);
	}

	WebPDecoderConfig config;
	if (0 == WebPInitDecoderConfig(&config)) {
	// ABI mismatch.
	// FIXME: New enum for this?
	return kInvalidInput;
	}

	// Free any memory associated with the buffer. Must be called last, so we declare it first.
	SkAutoTCallVProc<WebPDecBuffer, WebPFreeDecBuffer> autoFree(&(config.output));

	SkIRect bounds = SkIRect::MakeSize(this->getInfo().dimensions());
	if (options.fSubset) {
	// Caller is requesting a subset.
	if (!bounds.contains(*options.fSubset)) {
	// The subset is out of bounds.
	return kInvalidParameters;
	}

	bounds = *options.fSubset;

	// This is tricky. libwebp snaps the top and left to even values. We could let libwebp
	// do the snap, and return a subset which is a different one than requested. The problem
	// with that approach is that the caller may try to stitch subsets together, and if we
	// returned different subsets than requested, there would be artifacts at the boundaries.
	// Instead, we report that we cannot support odd values for top and left..
	if (!SkIsAlign2(bounds.fLeft) \|\| !SkIsAlign2(bounds.fTop)) {
	return kInvalidParameters;
	}

	#ifdef SK_DEBUG
	{
	// Make a copy, since getValidSubset can change its input.
	SkIRect subset(bounds);
	// That said, getValidSubset should not change its input, in this case; otherwise
	// getValidSubset does not match the actual subsets we can do.
	SkASSERT(this->getValidSubset(&subset) && subset == bounds);
	}
	#endif

	config.options.use_cropping = 1;
	config.options.crop_left = bounds.fLeft;
	config.options.crop_top = bounds.fTop;
	config.options.crop_width = bounds.width();
	config.options.crop_height = bounds.height();
	}

	SkISize dstDimensions = dstInfo.dimensions();
	if (bounds.size() != dstDimensions) {
	// Caller is requesting scaling.
	config.options.use_scaling = 1;
	config.options.scaled_width = dstDimensions.width();
	config.options.scaled_height = dstDimensions.height();
	}

	// FIXME (msarett):
	// Lossless webp is encoded as BGRA. In that case, it would be more efficient to
	// to decode BGRA and apply the color xform to a BGRA buffer.
	config.output.colorspace = colorXform ? MODE_RGBA :
	webp_decode_mode(dstInfo.colorType(), dstInfo.alphaType() == kPremul_SkAlphaType);
	config.output.is_external_memory = 1;

	// We will decode the entire image and then perform the color transform. libwebp
	// does not provide a row-by-row API. This is a shame particularly in the F16 case,
	// where we need to allocate an extra image-sized buffer.
	SkAutoTMalloc<uint32_t> pixels;
	if (kRGBA_F16_SkColorType == dstInfo.colorType()) {
	pixels.reset(dstDimensions.width() * dstDimensions.height());
	config.output.u.RGBA.rgba = (uint8_t*) pixels.get();
	config.output.u.RGBA.stride = (int) dstDimensions.width() * sizeof(uint32_t);
	config.output.u.RGBA.size = config.output.u.RGBA.stride * dstDimensions.height();
	} else {
	config.output.u.RGBA.rgba = (uint8_t*) dst;
	config.output.u.RGBA.stride = (int) rowBytes;
	config.output.u.RGBA.size = dstInfo.getSafeSize(rowBytes);
	}

	WebPIterator frame;
	SkAutoTCallVProc<WebPIterator, WebPDemuxReleaseIterator> autoFrame(&frame);
	// If this succeeded in NewFromStream(), it should succeed again here.
	SkAssertResult(WebPDemuxGetFrame(fDemux, 1, &frame));

	SkAutoTCallVProc<WebPIDecoder, WebPIDelete> idec(WebPIDecode(nullptr, 0, &config));
	if (!idec) {
	return kInvalidInput;
	}

	int rowsDecoded;
	SkCodec::Result result;
	switch (WebPIUpdate(idec, frame.fragment.bytes, frame.fragment.size)) {
	case VP8_STATUS_OK:
	rowsDecoded = dstInfo.height();
	result = kSuccess;
	break;
	case VP8_STATUS_SUSPENDED:
	WebPIDecGetRGB(idec, rowsDecodedPtr, nullptr, nullptr, nullptr);
	rowsDecoded = *rowsDecodedPtr;
	result = kIncompleteInput;
	break;
	default:
	return kInvalidInput;
	}

	if (colorXform) {
	SkColorSpaceXform::ColorFormat colorFormat = select_xform_format(dstInfo.colorType());
	SkAlphaType xformAlphaType = select_xform_alpha(dstInfo.alphaType(),
	this->getInfo().alphaType());

	uint32_t* src = (uint32_t*) config.output.u.RGBA.rgba;
	size_t srcRowBytes = config.output.u.RGBA.stride;
	for (int y = 0; y < rowsDecoded; y++) {
	colorXform->apply(dst, src, dstInfo.width(), colorFormat, xformAlphaType);
	dst = SkTAddOffset<void>(dst, rowBytes);
	src = SkTAddOffset<uint32_t>(src, srcRowBytes);
	}
	}

	return result;
	}

	SkWebpCodec::SkWebpCodec(int width, int height, const SkEncodedInfo& info,
	sk_sp<SkColorSpace> colorSpace, SkStream* stream, WebPDemuxer* demux,
	sk_sp<SkData> data)
	: INHERITED(width, height, info, stream, std::move(colorSpace))
	, fDemux(demux)
	, fData(std::move(data))
	{}