src/codec/SkWebpCodec.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 "src/codec/SkWebpCodec.h"

#include "include/codec/SkCodec.h"
#include "include/codec/SkCodecAnimation.h"
#include "include/codec/SkWebpDecoder.h"
#include "include/core/SkAlphaType.h"
#include "include/core/SkBitmap.h"
#include "include/core/SkColorType.h"
#include "include/core/SkImageInfo.h"
#include "include/core/SkRect.h"
#include "include/core/SkSize.h"
#include "include/core/SkStream.h"
#include "include/private/base/SkAlign.h"
#include "include/private/base/SkMath.h"
#include "include/private/base/SkNoncopyable.h"
#include "include/private/base/SkTFitsIn.h"
#include "include/private/base/SkTemplates.h"
#include "include/private/base/SkTo.h"
#include "modules/skcms/skcms.h"
#include "src/codec/SkParseEncodedOrigin.h"
#include "src/codec/SkSampler.h"
#include "src/core/SkRasterPipeline.h"
#include "src/core/SkRasterPipelineOpContexts.h"
#include "src/core/SkRasterPipelineOpList.h"
#include "src/core/SkStreamPriv.h"

#include <algorithm>
#include <cstdint>
#include <cstring>
#include <optional>
#include <tuple>
#include <utility>

// 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"  // NO_G3_REWRITE
#include "webp/demux.h"  // NO_G3_REWRITE
#include "webp/mux_types.h"  // NO_G3_REWRITE

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);
}

// This gives the optimal amount of the stream as SkData to a WebPDemux object for
// decoding so that an SkCodec object can be made.
// Exif data is at the end so we will end up reading the whole stream in that case.
// Otherwise we stop until we reach the header bytes for VP8(L) data, and the first
// frame for animated data.
// Returns a bool indicating if only the header has been read and the data read from
// the stream as SkData. If incomplete/invalid data, return nullptr and ignore the boolean
// value.
static std::pair<bool, sk_sp<SkData>> get_header_from_stream(SkStream* stream) {
    const size_t kBufferSize = 4096;
    char buffer[kBufferSize];
    // "RIFF" (4) + file size (4) + "WEBP" (4) = 12
    const size_t kInitialHeaderSize = 12;

    SkDynamicMemoryWStream tempStream;
    size_t bytes_read = stream->read(buffer, kInitialHeaderSize);
    if (bytes_read < kInitialHeaderSize ||
        memcmp(buffer, "RIFF", 4) != 0 ||
        memcmp(&buffer[8], "WEBP", 4) != 0) {
        // Fail if we don't have valid webp data
        return {false, nullptr};
    }
    tempStream.write(buffer, bytes_read);
    bool isAnimated = false;
    bool firstChunkRead = false;

    while (!stream->isAtEnd()) {
        // Read the chunk's FourCC and payload size
        const size_t kChunkSizeHeader = 8;
        bytes_read = stream->read(buffer, kChunkSizeHeader);
        if (bytes_read < kChunkSizeHeader) {
            return {false, nullptr};
        }
        tempStream.write(buffer, bytes_read);

        // Return upon VP8 or VP8L chunk, keep reading and writing otherwise
        // Handle ANMF subchunks, if animated image read the first frame and return
        if (!memcmp(buffer, "VP8 ", 4)) {
            const size_t kVP8UncompressedChunkMinSize = 3;
            const size_t kVP8UncompressedChunkMaxSize = 10;
            bytes_read = stream->read(buffer, kVP8UncompressedChunkMaxSize);
            if (bytes_read < kVP8UncompressedChunkMinSize) {
                // Invalid webp
                return {false, nullptr};
            }
            tempStream.write(buffer, bytes_read);
            return {true, tempStream.detachAsData()};
        } else if (!memcmp(buffer, "VP8L", 4)) {
            const size_t kImageHeaderSize = 5;
            bytes_read = stream->read(buffer, kImageHeaderSize);
            if (bytes_read < kImageHeaderSize) {
                // Invalid webp
                return {false, nullptr};
            }
            tempStream.write(buffer, bytes_read);
            return {true, tempStream.detachAsData()};
        } else if (!memcmp(buffer, "VP8X", 4)) {
            if (firstChunkRead) {
                return {false, nullptr};
            } else {
                firstChunkRead = true;
            }
            // VP8X payload should always be 10
            uint32_t payloadSize;
            const size_t kVP8XPayloadSize = 10;
            memcpy(&payloadSize, &buffer[4], 4);
            if (payloadSize != kVP8XPayloadSize) {
                return {false, nullptr};
            }

            bytes_read = stream->read(buffer, payloadSize);
            if (bytes_read < payloadSize) {
              // Invalid webp
              return {false, nullptr};
            }
            tempStream.write(buffer, bytes_read);

            uint8_t vp8xFeatureFlags;
            memcpy(&vp8xFeatureFlags, buffer, 1);
            const bool hasExif = vp8xFeatureFlags & EXIF_FLAG;
            isAnimated = vp8xFeatureFlags & ANIMATION_FLAG;
            if (hasExif) {
                // If exif data, we have to read the whole stream because exif data
                // is at the end of the file and we want that in order to create
                // the SkCodec
                do {
                  bytes_read = stream->read(buffer, kBufferSize);
                  tempStream.write(buffer, bytes_read);
                } while (!stream->isAtEnd());
                return {false, tempStream.detachAsData()};
            }
        } else {
            if (!firstChunkRead) {
                // We only expect VP8, VP8L, or VP8X chunks to be the first.
                return {false, nullptr};
            }
            const bool animatedFrame = !memcmp(buffer, "ANMF", 4);

            // According to the RIFF document format, if 'payloadSize' is odd a single
            // padding byte -- which must be 0 to conform with RIFF -- is added.
            uint32_t payloadSize;
            memcpy(&payloadSize, &buffer[4], 4);
            if (payloadSize % 2 != 0) {
                payloadSize += 1;
            }

            // Read 'payload size' bytes ahead to get to the next chunk
            while (payloadSize) {
                bytes_read = stream->read(buffer, std::min((size_t)payloadSize, kBufferSize));
                if (!bytes_read) {
                    break;
                }
                tempStream.write(buffer, bytes_read);
                payloadSize -= bytes_read;
            }
            if (payloadSize) {
                SkASSERT(stream->isAtEnd());
                // Invalid webp
                return {false, nullptr};
            }

            if (animatedFrame && isAnimated) {
                // If this is an animated frame and we are expecting it, return
                // the whole frame (this is the first frame which we want in order to
                // create the SkCodec)
                return {true, tempStream.detachAsData()};
            }
        }
    }
    // We never reached image data but read the whole stream
    return {true, tempStream.detachAsData()};
}

bool SkWebpCodec::ensureAllData() {
    if (fOnlyHeaderParsed) {
        SkDynamicMemoryWStream newData;
        newData.write(fData->data(), fData->size());
        SkStreamCopy(&newData, this->stream());
        fData = newData.detachAsData();
        fOnlyHeaderParsed = false;

        WebPData webpData = { fData->bytes(), fData->size() };
        WebPDemuxState state;
        fDemux.reset(WebPDemuxPartial(&webpData, &state));
        // We know fDemux state is at least WEBP_DEMUX_PARSED_HEADER already which we allow
        if (state == WEBP_DEMUX_PARSE_ERROR) {
            return false;
        }
    }
    return true;
}

// Parse headers of RIFF container, and check for valid Webp (VP8) content.
// Returns an SkWebpCodec on success
std::unique_ptr<SkCodec> SkWebpCodec::MakeFromStream(std::unique_ptr<SkStream> stream,
                                                     Result* result) {
    SkASSERT(result);
    if (!stream) {
        *result = SkCodec::kInvalidInput;
        return nullptr;
    }
    // Webp demux needs a contiguous data buffer.
    sk_sp<SkData> data = nullptr;
    // If there is no memory base for the stream, we will attempt to only read necessary portions,
    // which we will read the rest later.
    bool onlyHeaderParsed = false;
    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 {
        std::tie(onlyHeaderParsed, data) = get_header_from_stream(stream.get());
        if (!data) {
            *result = kIncompleteInput;
            return nullptr;
        }

        // If we are forced to copy the stream to a data, we can go ahead and delete the stream.
        if (!onlyHeaderParsed) {
            stream.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() };
    WebPDemuxState state;
    SkAutoTCallVProc<WebPDemuxer, WebPDemuxDelete> demux(WebPDemuxPartial(&webpData, &state));
    switch (state) {
        case WEBP_DEMUX_PARSE_ERROR:
            *result = kInvalidInput;
            return nullptr;
        case WEBP_DEMUX_PARSING_HEADER:
            *result = kIncompleteInput;
            return nullptr;
        case WEBP_DEMUX_PARSED_HEADER:
        case WEBP_DEMUX_DONE:
            SkASSERT(demux);
            break;
    }

    const int width = WebPDemuxGetI(demux, WEBP_FF_CANVAS_WIDTH);
    const int height = WebPDemuxGetI(demux, WEBP_FF_CANVAS_HEIGHT);

    // Validate the image size that's about to be decoded.
    {
        const int64_t size = sk_64_mul(width, height);
        // now check that if we are 4-bytes per pixel, we also don't overflow
        if (!SkTFitsIn<int32_t>(size) || SkTo<int32_t>(size) > (0x7FFFFFFF >> 2)) {
            *result = kInvalidInput;
            return nullptr;
        }
    }

    std::unique_ptr<SkEncodedInfo::ICCProfile> profile = nullptr;
    {
        WebPChunkIterator chunkIterator;
        SkAutoTCallVProc<WebPChunkIterator, WebPDemuxReleaseChunkIterator> autoCI(&chunkIterator);
        if (WebPDemuxGetChunk(demux, "ICCP", 1, &chunkIterator)) {
            // FIXME: I think this could be MakeWithoutCopy
            auto chunk = SkData::MakeWithCopy(chunkIterator.chunk.bytes, chunkIterator.chunk.size);
            profile = SkEncodedInfo::ICCProfile::Make(std::move(chunk));
        }
        if (profile && profile->profile()->data_color_space != skcms_Signature_RGB) {
            profile = nullptr;
        }
    }

    SkEncodedOrigin origin = kDefault_SkEncodedOrigin;
    {
        WebPChunkIterator chunkIterator;
        SkAutoTCallVProc<WebPChunkIterator, WebPDemuxReleaseChunkIterator> autoCI(&chunkIterator);
        if (WebPDemuxGetChunk(demux, "EXIF", 1, &chunkIterator)) {
            SkParseEncodedOrigin(chunkIterator.chunk.bytes, chunkIterator.chunk.size, &origin);
        }
    }

    // Get the first frame and its "features" to determine the color and alpha types.
    WebPIterator frame;
    SkAutoTCallVProc<WebPIterator, WebPDemuxReleaseIterator> autoFrame(&frame);
    if (!WebPDemuxGetFrame(demux, 1, &frame)) {
        *result = kIncompleteInput;
        return nullptr;
    }

    WebPBitstreamFeatures features;
    switch (WebPGetFeatures(frame.fragment.bytes, frame.fragment.size, &features)) {
        case VP8_STATUS_OK:
            break;
        case VP8_STATUS_SUSPENDED:
        case VP8_STATUS_NOT_ENOUGH_DATA:
            *result = kIncompleteInput;
            return nullptr;
        default:
            *result = kInvalidInput;
            return nullptr;
    }

    const bool hasAlpha = SkToBool(frame.has_alpha)
            || frame.width != width || frame.height != height;
    SkEncodedInfo::Color color;
    SkEncodedInfo::Alpha alpha;
    switch (features.format) {
        case 0:
            // This indicates a "mixed" format.  We could see this for
            // animated webps (multiple fragments).
            // 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.
            [[fallthrough]];
        case 2:
            // This is the lossless format (BGRA).
            if (hasAlpha) {
                color = SkEncodedInfo::kBGRA_Color;
                alpha = SkEncodedInfo::kUnpremul_Alpha;
            } else {
                color = SkEncodedInfo::kBGRX_Color;
                alpha = SkEncodedInfo::kOpaque_Alpha;
            }
            break;
        case 1:
            // This is the lossy format (YUV).
            if (hasAlpha) {
                color = SkEncodedInfo::kYUVA_Color;
                alpha = SkEncodedInfo::kUnpremul_Alpha;
            } else {
                color = SkEncodedInfo::kYUV_Color;
                alpha = SkEncodedInfo::kOpaque_Alpha;
            }
            break;
        default:
            *result = kInvalidInput;
            return nullptr;
    }


    *result = kSuccess;
    SkEncodedInfo info = SkEncodedInfo::Make(width, height, color, alpha, 8, std::move(profile));
    return std::unique_ptr<SkCodec>(new SkWebpCodec(std::move(info), std::move(stream),
                                                    demux.release(), std::move(data), origin,
                                                    onlyHeaderParsed));
}

static WEBP_CSP_MODE webp_decode_mode(SkColorType dstCT, bool premultiply) {
    switch (dstCT) {
        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;
    }
}

SkWebpCodec::Frame* SkWebpCodec::FrameHolder::appendNewFrame(bool hasAlpha) {
    const int i = this->size();
    fFrames.emplace_back(i, hasAlpha ? SkEncodedInfo::kUnpremul_Alpha
                                     : SkEncodedInfo::kOpaque_Alpha);
    return &fFrames[i];
}

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

    if (!this->bounds().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;
}

int SkWebpCodec::onGetRepetitionCount() {
    auto flags = WebPDemuxGetI(fDemux.get(), WEBP_FF_FORMAT_FLAGS);
    if (!(flags & ANIMATION_FLAG)) {
        return 0;
    }

    int loopCount = WebPDemuxGetI(fDemux.get(), WEBP_FF_LOOP_COUNT);
    if (0 == loopCount) {
        return kRepetitionCountInfinite;
    }

    loopCount--;
    return loopCount;
}

SkCodec::IsAnimated SkWebpCodec::onIsAnimated() {
    auto flags = WebPDemuxGetI(fDemux.get(), WEBP_FF_FORMAT_FLAGS);
    return (flags & ANIMATION_FLAG) != 0 ? IsAnimated::kYes : IsAnimated::kNo;
}

bool SkWebpCodec::onRewind() {
    // We may have a stream, but we never need to rewind it because we hold our own
    // SkData copy.
    return true;
}

int SkWebpCodec::onGetFrameCount() {
    auto flags = WebPDemuxGetI(fDemux.get(), WEBP_FF_FORMAT_FLAGS);
    if (!(flags & ANIMATION_FLAG)) {
        return 1;
    }

    const uint32_t oldFrameCount = fFrameHolder.size();
    if (fFailed) {
        return oldFrameCount;
    }

    if (!ensureAllData()) {
        return 0;
    }

    const uint32_t frameCount = WebPDemuxGetI(fDemux, WEBP_FF_FRAME_COUNT);
    if (oldFrameCount == frameCount) {
        // We have already parsed this.
        return frameCount;
    }

    fFrameHolder.reserve(frameCount);

    for (uint32_t i = oldFrameCount; i < frameCount; i++) {
        WebPIterator iter;
        SkAutoTCallVProc<WebPIterator, WebPDemuxReleaseIterator> autoIter(&iter);

        if (!WebPDemuxGetFrame(fDemux.get(), i + 1, &iter)) {
            fFailed = true;
            break;
        }

        // libwebp only reports complete frames of an animated image.
        SkASSERT(iter.complete);

        Frame* frame = fFrameHolder.appendNewFrame(iter.has_alpha);
        frame->setXYWH(iter.x_offset, iter.y_offset, iter.width, iter.height);
        frame->setDisposalMethod(iter.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND ?
                SkCodecAnimation::DisposalMethod::kRestoreBGColor :
                SkCodecAnimation::DisposalMethod::kKeep);
        frame->setDuration(iter.duration);
        if (WEBP_MUX_BLEND != iter.blend_method) {
            frame->setBlend(SkCodecAnimation::Blend::kSrc);
        }
        fFrameHolder.setAlphaAndRequiredFrame(frame);
    }

    return fFrameHolder.size();

}

const SkFrame* SkWebpCodec::FrameHolder::onGetFrame(int i) const {
    return static_cast<const SkFrame*>(this->frame(i));
}

const SkWebpCodec::Frame* SkWebpCodec::FrameHolder::frame(int i) const {
    SkASSERT(i >= 0 && i < this->size());
    return &fFrames[i];
}

bool SkWebpCodec::onGetFrameInfo(int i, FrameInfo* frameInfo) const {
    if (i >= fFrameHolder.size()) {
        return false;
    }

    const Frame* frame = fFrameHolder.frame(i);
    if (!frame) {
        return false;
    }

    if (frameInfo) {
        // libwebp only reports fully received frames for an
        // animated image.
        frame->fillIn(frameInfo, true);
    }

    return true;
}

static bool is_8888(SkColorType colorType) {
    switch (colorType) {
        case kRGBA_8888_SkColorType:
        case kBGRA_8888_SkColorType:
            return true;
        default:
            return false;
    }
}

namespace {

// Requires that the src input be unpremultiplied (or opaque).
class RPBlender final : SkNoncopyable {
public:
    RPBlender(SkColorType dstCT, SkColorType srcCT, SkAlphaType dstAt, bool srcHasAlpha)
    {
        fRP.appendLoadDst(dstCT, &fDstCtx);
        if (kUnpremul_SkAlphaType == dstAt) {
            fRP.append(SkRasterPipelineOp::premul_dst);
        }

        fRP.appendLoad(srcCT, &fSrcCtx);
        if (srcHasAlpha) {
            fRP.append(SkRasterPipelineOp::premul);
        }

        fRP.append(SkRasterPipelineOp::srcover);

        if (kUnpremul_SkAlphaType == dstAt) {
            fRP.append(SkRasterPipelineOp::unpremul);
        }
        fRP.appendStore(dstCT, &fDstCtx);
    }

    void blendLine(void* dst, const void* src, int width) {
        fDstCtx = {                    dst, 0 };
        fSrcCtx = { const_cast<void*>(src), 0 };

        fRP.run(0, 0, width, 1);
    }

private:
    SkRasterPipelineContexts::MemoryCtx fDstCtx, fSrcCtx;

    SkRasterPipeline_<256> fRP;
};

}  // namespace

SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
                                         const Options& options, int* rowsDecodedPtr) {
    const int index = options.fFrameIndex;
    SkASSERT(0 == index || index < fFrameHolder.size());
    SkASSERT(0 == index || !options.fSubset);

    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));

    WebPIterator frame;
    SkAutoTCallVProc<WebPIterator, WebPDemuxReleaseIterator> autoFrame(&frame);
    // If this succeeded in onGetFrameCount(), it should succeed again here.
    if (!ensureAllData()) {
        return kInvalidInput;
    }
    SkAssertResult(WebPDemuxGetFrame(fDemux, index + 1, &frame));

    const bool independent = index == 0 ? true :
            (fFrameHolder.frame(index)->getRequiredFrame() == kNoFrame);
    // Get the frameRect.  libwebp will have already signaled an error if this is not fully
    // contained by the canvas.
    auto frameRect = SkIRect::MakeXYWH(frame.x_offset, frame.y_offset, frame.width, frame.height);
    SkASSERT(this->bounds().contains(frameRect));
    const bool frameIsSubset = frameRect != this->bounds();
    if (independent && frameIsSubset) {
        SkSampler::Fill(dstInfo, dst, rowBytes, options.fZeroInitialized);
    }

    int dstX = frameRect.x();
    int dstY = frameRect.y();
    int subsetWidth = frameRect.width();
    int subsetHeight = frameRect.height();
    if (options.fSubset) {
        SkIRect subset = *options.fSubset;
        SkASSERT(this->bounds().contains(subset));
        SkASSERT(SkIsAlign2(subset.fLeft) && SkIsAlign2(subset.fTop));
        SkASSERT(this->getValidSubset(&subset) && subset == *options.fSubset);

        if (!SkIRect::Intersects(subset, frameRect)) {
            return kSuccess;
        }

        int minXOffset = std::min(dstX, subset.x());
        int minYOffset = std::min(dstY, subset.y());
        dstX -= minXOffset;
        dstY -= minYOffset;
        frameRect.offset(-minXOffset, -minYOffset);
        subset.offset(-minXOffset, -minYOffset);

        // Just like we require that the requested subset x and y offset are even, libwebp
        // guarantees that the frame x and y offset are even (it's actually impossible to specify
        // an odd frame offset).  So we can still guarantee that the adjusted offsets are even.
        SkASSERT(SkIsAlign2(subset.fLeft) && SkIsAlign2(subset.fTop));

        SkIRect intersection;
        SkAssertResult(intersection.intersect(frameRect, subset));
        subsetWidth = intersection.width();
        subsetHeight = intersection.height();

        config.options.use_cropping = 1;
        config.options.crop_left = subset.x();
        config.options.crop_top = subset.y();
        config.options.crop_width = subsetWidth;
        config.options.crop_height = subsetHeight;
    }

    // Ignore the frame size and offset when determining if scaling is necessary.
    int scaledWidth = subsetWidth;
    int scaledHeight = subsetHeight;
    SkISize srcSize = options.fSubset ? options.fSubset->size() : this->dimensions();
    if (srcSize != dstInfo.dimensions()) {
        config.options.use_scaling = 1;

        if (frameIsSubset) {
            float scaleX = ((float) dstInfo.width()) / srcSize.width();
            float scaleY = ((float) dstInfo.height()) / srcSize.height();

            // We need to be conservative here and floor rather than round.
            // Otherwise, we may find ourselves decoding off the end of memory.
            dstX = scaleX * dstX;
            scaledWidth = scaleX * scaledWidth;
            dstY = scaleY * dstY;
            scaledHeight = scaleY * scaledHeight;
            if (0 == scaledWidth || 0 == scaledHeight) {
                return kSuccess;
            }
        } else {
            scaledWidth = dstInfo.width();
            scaledHeight = dstInfo.height();
        }

        config.options.scaled_width = scaledWidth;
        config.options.scaled_height = scaledHeight;
    }

    const bool blendWithPrevFrame = !independent && frame.blend_method == WEBP_MUX_BLEND
        && frame.has_alpha;

    auto webpInfo = dstInfo;
    if (!frame.has_alpha) {
        webpInfo = webpInfo.makeAlphaType(kOpaque_SkAlphaType);
    } else if (this->colorXform() || blendWithPrevFrame) {
        // the colorXform and blend_line expect unpremul.
        webpInfo = webpInfo.makeAlphaType(kUnpremul_SkAlphaType);
    }
    if (this->colorXform()) {
        // Swizzling between RGBA and BGRA is zero cost in a color transform.  So when we have a
        // color transform, we should decode to whatever is easiest for libwebp, and then let the
        // color transform swizzle if necessary.
        // Lossy webp is encoded as YUV (so RGBA and BGRA are the same cost).  Lossless webp is
        // encoded as BGRA. This means decoding to BGRA is either faster or the same cost as RGBA.
        webpInfo = webpInfo.makeColorType(kBGRA_8888_SkColorType);
    }

    SkBitmap webpDst;
    if ((this->colorXform() && !is_8888(dstInfo.colorType())) || blendWithPrevFrame) {
        // 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 when we do not want
        // 8888, since we will need to create another image sized buffer.
        webpDst.allocPixels(webpInfo);
    } else {
        // libwebp can decode directly into the output memory.
        webpDst.installPixels(webpInfo, dst, rowBytes);
    }

    config.output.colorspace = webp_decode_mode(webpInfo.colorType(),
            webpInfo.alphaType() == kPremul_SkAlphaType);
    config.output.is_external_memory = 1;

    config.output.u.RGBA.rgba = reinterpret_cast<uint8_t*>(webpDst.getAddr(dstX, dstY));
    config.output.u.RGBA.stride = static_cast<int>(webpDst.rowBytes());
    config.output.u.RGBA.size = webpDst.computeByteSize();

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

    int rowsDecoded = 0;
    SkCodec::Result result;
    switch (WebPIUpdate(idec, frame.fragment.bytes, frame.fragment.size)) {
        case VP8_STATUS_OK:
            rowsDecoded = scaledHeight;
            result = kSuccess;
            break;
        case VP8_STATUS_SUSPENDED:
            if (!WebPIDecGetRGB(idec, &rowsDecoded, nullptr, nullptr, nullptr)
                    || rowsDecoded <= 0) {
                return kInvalidInput;
            }
            *rowsDecodedPtr = rowsDecoded + dstY;
            result = kIncompleteInput;
            break;
        default:
            return kInvalidInput;
    }

    const size_t dstBpp = dstInfo.bytesPerPixel();
    dst = SkTAddOffset<void>(dst, dstBpp * dstX + rowBytes * dstY);
    const size_t srcRowBytes = config.output.u.RGBA.stride;

    const auto dstCT = dstInfo.colorType();
    if (this->colorXform()) {
        uint32_t* xformSrc = (uint32_t*) config.output.u.RGBA.rgba;
        SkBitmap tmp;
        void* xformDst;

        if (blendWithPrevFrame) {
            // Xform into temporary bitmap big enough for one row.
            tmp.allocPixels(dstInfo.makeWH(scaledWidth, 1));
            xformDst = tmp.getPixels();
        } else {
            xformDst = dst;
        }

        std::optional<RPBlender> blender;
        if (blendWithPrevFrame) {
            blender.emplace(dstCT, dstCT, dstInfo.alphaType(), frame.has_alpha);
        }

        for (int y = 0; y < rowsDecoded; y++) {
            this->applyColorXform(xformDst, xformSrc, scaledWidth);
            if (blendWithPrevFrame) {
                blender->blendLine(dst, xformDst, scaledWidth);
                dst = SkTAddOffset<void>(dst, rowBytes);
            } else {
                xformDst = SkTAddOffset<void>(xformDst, rowBytes);
            }
            xformSrc = SkTAddOffset<uint32_t>(xformSrc, srcRowBytes);
        }
    } else if (blendWithPrevFrame) {
        RPBlender blender(dstCT, webpDst.colorType(), dstInfo.alphaType(), frame.has_alpha);

        const uint8_t* src = config.output.u.RGBA.rgba;

        for (int y = 0; y < rowsDecoded; y++) {
            blender.blendLine(dst, src, scaledWidth);
            src = SkTAddOffset<const uint8_t>(src, srcRowBytes);
            dst = SkTAddOffset<void>(dst, rowBytes);
        }
    }

    return result;
}

SkWebpCodec::SkWebpCodec(SkEncodedInfo&& info, std::unique_ptr<SkStream> stream,
                         WebPDemuxer* demux, sk_sp<SkData> data, SkEncodedOrigin origin,
                         bool onlyHeaderParsed)
    : INHERITED(std::move(info), skcms_PixelFormat_BGRA_8888, std::move(stream),
                origin)
    , fDemux(demux)
    , fData(std::move(data))
    , fFailed(false)
    , fOnlyHeaderParsed(onlyHeaderParsed)
{
    const auto& eInfo = this->getEncodedInfo();
    fFrameHolder.setScreenSize(eInfo.width(), eInfo.height());
}

namespace SkWebpDecoder {
bool IsWebp(const void* data, size_t len) {
    return SkWebpCodec::IsWebp(data, len);
}

std::unique_ptr<SkCodec> Decode(std::unique_ptr<SkStream> stream,
                                SkCodec::Result* outResult,
                                SkCodecs::DecodeContext) {
    SkCodec::Result resultStorage;
    if (!outResult) {
        outResult = &resultStorage;
    }
    return SkWebpCodec::MakeFromStream(std::move(stream), outResult);
}

std::unique_ptr<SkCodec> Decode(sk_sp<SkData> data,
                                SkCodec::Result* outResult,
                                SkCodecs::DecodeContext) {
    if (!data) {
        if (outResult) {
            *outResult = SkCodec::kInvalidInput;
        }
        return nullptr;
    }
    return Decode(SkMemoryStream::Make(std::move(data)), outResult, nullptr);
}
}  // namespace SkWebpDecoder