C++ SkImageInfo::makeWH方法代码示例

void SkCodec::fillIncompleteImage(const SkImageInfo& info, void* dst, size_t rowBytes,
        ZeroInitialized zeroInit, int linesRequested, int linesDecoded) {

    void* fillDst;
    const uint32_t fillValue = this->getFillValue(info.colorType(), info.alphaType());
    const int linesRemaining = linesRequested - linesDecoded;
    SkSampler* sampler = this->getSampler(false);

    switch (this->getScanlineOrder()) {
        case kTopDown_SkScanlineOrder:
        case kNone_SkScanlineOrder: {
            const SkImageInfo fillInfo = info.makeWH(info.width(), linesRemaining);
            fillDst = SkTAddOffset<void>(dst, linesDecoded * rowBytes);
            fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
            break;
        }
        case kBottomUp_SkScanlineOrder: {
            fillDst = dst;
            const SkImageInfo fillInfo = info.makeWH(info.width(), linesRemaining);
            fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
            break;
        }
        case kOutOfOrder_SkScanlineOrder: {
            SkASSERT(1 == linesRequested || this->getInfo().height() == linesRequested);
            const SkImageInfo fillInfo = info.makeWH(info.width(), 1);
            for (int srcY = linesDecoded; srcY < linesRequested; srcY++) {
                fillDst = SkTAddOffset<void>(dst, this->outputScanline(srcY) * rowBytes);
                fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
            }
            break;
        }
    }
}

bool SkPixmap::readPixels(const SkImageInfo& requestedDstInfo, void* dstPixels, size_t dstRB,
                          int x, int y) const {
    if (kUnknown_SkColorType == requestedDstInfo.colorType()) {
        return false;
    }
    if (nullptr == dstPixels || dstRB < requestedDstInfo.minRowBytes()) {
        return false;
    }
    if (0 == requestedDstInfo.width() || 0 == requestedDstInfo.height()) {
        return false;
    }
    
    SkIRect srcR = SkIRect::MakeXYWH(x, y, requestedDstInfo.width(), requestedDstInfo.height());
    if (!srcR.intersect(0, 0, this->width(), this->height())) {
        return false;
    }
    
    // the intersect may have shrunk info's logical size
    const SkImageInfo dstInfo = requestedDstInfo.makeWH(srcR.width(), srcR.height());
    
    // if x or y are negative, then we have to adjust pixels
    if (x > 0) {
        x = 0;
    }
    if (y > 0) {
        y = 0;
    }
    // here x,y are either 0 or negative
    dstPixels = ((char*)dstPixels - y * dstRB - x * dstInfo.bytesPerPixel());

    const SkImageInfo srcInfo = this->info().makeWH(dstInfo.width(), dstInfo.height());
    const void* srcPixels = this->addr(srcR.x(), srcR.y());
    return SkPixelInfo::CopyPixels(dstInfo, dstPixels, dstRB,
                                   srcInfo, srcPixels, this->rowBytes(), this->ctable());
}

/*
 * Performs the decoding
 */
int SkBmpMaskCodec::decodeRows(const SkImageInfo& dstInfo,
                                           void* dst, size_t dstRowBytes,
                                           const Options& opts) {
    // Iterate over rows of the image
    uint8_t* srcRow = fSrcBuffer.get();
    const int height = dstInfo.height();
    for (int y = 0; y < height; y++) {
        // Read a row of the input
        if (this->stream()->read(srcRow, this->srcRowBytes()) != this->srcRowBytes()) {
            SkCodecPrintf("Warning: incomplete input stream.\n");
            return y;
        }

        // Decode the row in destination format
        uint32_t row = this->getDstRow(y, height);
        void* dstRow = SkTAddOffset<void>(dst, row * dstRowBytes);

        if (this->colorXform()) {
            SkImageInfo xformInfo = dstInfo.makeWH(fMaskSwizzler->swizzleWidth(), dstInfo.height());
            fMaskSwizzler->swizzle(this->xformBuffer(), srcRow);
            this->applyColorXform(xformInfo, dstRow, this->xformBuffer());
        } else {
            fMaskSwizzler->swizzle(dstRow, srcRow);
        }
    }

    // Finished decoding the entire image
    return height;
}

// Much of readPixels is exercised by copyTo testing, since readPixels is the backend for that
// method. Here we explicitly test subset copies.
//
DEF_TEST(BitmapReadPixels, reporter) {
    const int W = 4;
    const int H = 4;
    const size_t rowBytes = W * sizeof(SkPMColor);
    const SkImageInfo srcInfo = SkImageInfo::MakeN32Premul(W, H);
    SkPMColor srcPixels[16];
    fill_4x4_pixels(srcPixels);
    SkBitmap srcBM;
    srcBM.installPixels(srcInfo, srcPixels, rowBytes);

    SkImageInfo dstInfo = SkImageInfo::MakeN32Premul(W, H);
    SkPMColor dstPixels[16];

    const struct {
        bool     fExpectedSuccess;
        SkIPoint fRequestedSrcLoc;
        SkISize  fRequestedDstSize;
        // If fExpectedSuccess, check these, otherwise ignore
        SkIPoint fExpectedDstLoc;
        SkIRect  fExpectedSrcR;
    } gRec[] = {
        { true,  { 0, 0 }, { 4, 4 }, { 0, 0 }, { 0, 0, 4, 4 } },
        { true,  { 1, 1 }, { 2, 2 }, { 0, 0 }, { 1, 1, 3, 3 } },
        { true,  { 2, 2 }, { 4, 4 }, { 0, 0 }, { 2, 2, 4, 4 } },
        { true,  {-1,-1 }, { 2, 2 }, { 1, 1 }, { 0, 0, 1, 1 } },
        { false, {-1,-1 }, { 1, 1 }, { 0, 0 }, { 0, 0, 0, 0 } },
    };

    for (size_t i = 0; i < SK_ARRAY_COUNT(gRec); ++i) {
        clear_4x4_pixels(dstPixels);

        dstInfo = dstInfo.makeWH(gRec[i].fRequestedDstSize.width(),
                                 gRec[i].fRequestedDstSize.height());
        bool success = srcBM.readPixels(dstInfo, dstPixels, rowBytes,
                                        gRec[i].fRequestedSrcLoc.x(), gRec[i].fRequestedSrcLoc.y());

        REPORTER_ASSERT(reporter, gRec[i].fExpectedSuccess == success);
        if (success) {
            const SkIRect srcR = gRec[i].fExpectedSrcR;
            const int dstX = gRec[i].fExpectedDstLoc.x();
            const int dstY = gRec[i].fExpectedDstLoc.y();
            // Walk the dst pixels, and check if we got what we expected
            for (int y = 0; y < H; ++y) {
                for (int x = 0; x < W; ++x) {
                    SkPMColor dstC = dstPixels[y*4+x];
                    // get into src coordinates
                    int sx = x - dstX + srcR.x();
                    int sy = y - dstY + srcR.y();
                    if (srcR.contains(sx, sy)) {
                        REPORTER_ASSERT(reporter, check_4x4_pixel(dstC, sx, sy));
                    } else {
                        REPORTER_ASSERT(reporter, 0 == dstC);
                    }
                }
            }
        }
    }
}

static void test_newraster(skiatest::Reporter* reporter) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(10, 10);
    const size_t minRowBytes = info.minRowBytes();
    const size_t size = info.getSafeSize(minRowBytes);
    SkAutoMalloc storage(size);
    SkPMColor* baseAddr = static_cast<SkPMColor*>(storage.get());
    sk_bzero(baseAddr, size);

    SkCanvas* canvas = SkCanvas::NewRasterDirect(info, baseAddr, minRowBytes);
    REPORTER_ASSERT(reporter, canvas);

    SkImageInfo info2;
    size_t rowBytes;
    const SkPMColor* addr = (const SkPMColor*)canvas->peekPixels(&info2, &rowBytes);
    REPORTER_ASSERT(reporter, addr);
    REPORTER_ASSERT(reporter, info == info2);
    REPORTER_ASSERT(reporter, minRowBytes == rowBytes);
    for (int y = 0; y < info.height(); ++y) {
        for (int x = 0; x < info.width(); ++x) {
            REPORTER_ASSERT(reporter, 0 == addr[x]);
        }
        addr = (const SkPMColor*)((const char*)addr + rowBytes);
    }
    SkDELETE(canvas);

    // now try a deliberately bad info
    info = info.makeWH(-1, info.height());
    REPORTER_ASSERT(reporter, NULL == SkCanvas::NewRasterDirect(info, baseAddr, minRowBytes));

    // too big
    info = info.makeWH(1 << 30, 1 << 30);
    REPORTER_ASSERT(reporter, NULL == SkCanvas::NewRasterDirect(info, baseAddr, minRowBytes));

    // not a valid pixel type
    info = SkImageInfo::Make(10, 10, kUnknown_SkColorType, info.alphaType());
    REPORTER_ASSERT(reporter, NULL == SkCanvas::NewRasterDirect(info, baseAddr, minRowBytes));

    // We should succeed with a zero-sized valid info
    info = SkImageInfo::MakeN32Premul(0, 0);
    canvas = SkCanvas::NewRasterDirect(info, baseAddr, minRowBytes);
    REPORTER_ASSERT(reporter, canvas);
    SkDELETE(canvas);
}

static void check_fill(skiatest::Reporter* r,
                       const SkImageInfo& imageInfo,
                       uint32_t startRow,
                       uint32_t endRow,
                       size_t rowBytes,
                       uint32_t offset,
                       uint32_t colorOrIndex) {

    // Calculate the total size of the image in bytes.  Use the smallest possible size.
    // The offset value tells us to adjust the pointer from the memory we allocate in order
    // to test on different memory alignments.  If offset is nonzero, we need to increase the
    // size of the memory we allocate in order to make sure that we have enough.  We are
    // still allocating the smallest possible size.
    const size_t totalBytes = imageInfo.getSafeSize(rowBytes) + offset;

    // Create fake image data where every byte has a value of 0
    SkAutoTDeleteArray<uint8_t> storage(new uint8_t[totalBytes]);
    memset(storage.get(), 0, totalBytes);
    // Adjust the pointer in order to test on different memory alignments
    uint8_t* imageData = storage.get() + offset;
    uint8_t* imageStart = imageData + rowBytes * startRow;
    const SkImageInfo fillInfo = imageInfo.makeWH(imageInfo.width(), endRow - startRow + 1);
    SkSampler::Fill(fillInfo, imageStart, rowBytes, colorOrIndex, SkCodec::kNo_ZeroInitialized);

    // Ensure that the pixels are filled properly
    // The bots should catch any memory corruption
    uint8_t* indexPtr = imageData + startRow * rowBytes;
    uint8_t* grayPtr = indexPtr;
    uint32_t* colorPtr = (uint32_t*) indexPtr;
    uint16_t* color565Ptr = (uint16_t*) indexPtr;
    for (uint32_t y = startRow; y <= endRow; y++) {
        for (int32_t x = 0; x < imageInfo.width(); x++) {
            switch (imageInfo.colorType()) {
                case kIndex_8_SkColorType:
                    REPORTER_ASSERT(r, kFillIndex == indexPtr[x]);
                    break;
                case kN32_SkColorType:
                    REPORTER_ASSERT(r, kFillColor == colorPtr[x]);
                    break;
                case kGray_8_SkColorType:
                    REPORTER_ASSERT(r, kFillGray == grayPtr[x]);
                    break;
                case kRGB_565_SkColorType:
                    REPORTER_ASSERT(r, kFill565 == color565Ptr[x]);
                    break;
                default:
                    REPORTER_ASSERT(r, false);
                    break;
            }
        }
        indexPtr += rowBytes;
        colorPtr = (uint32_t*) indexPtr;
    }
}

static void test_newraster(skiatest::Reporter* reporter) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(10, 10);
    const size_t minRowBytes = info.minRowBytes();
    const size_t size = info.getSafeSize(minRowBytes);
    SkAutoTMalloc<SkPMColor> storage(size);
    SkPMColor* baseAddr = storage.get();
    sk_bzero(baseAddr, size);

    std::unique_ptr<SkCanvas> canvas = SkCanvas::MakeRasterDirect(info, baseAddr, minRowBytes);
    REPORTER_ASSERT(reporter, canvas);

    SkPixmap pmap;
    const SkPMColor* addr = canvas->peekPixels(&pmap) ? pmap.addr32() : nullptr;
    REPORTER_ASSERT(reporter, addr);
    REPORTER_ASSERT(reporter, info == pmap.info());
    REPORTER_ASSERT(reporter, minRowBytes == pmap.rowBytes());
    for (int y = 0; y < info.height(); ++y) {
        for (int x = 0; x < info.width(); ++x) {
            REPORTER_ASSERT(reporter, 0 == addr[x]);
        }
        addr = (const SkPMColor*)((const char*)addr + pmap.rowBytes());
    }

    // now try a deliberately bad info
    info = info.makeWH(-1, info.height());
    REPORTER_ASSERT(reporter, nullptr == SkCanvas::MakeRasterDirect(info, baseAddr, minRowBytes));

    // too big
    info = info.makeWH(1 << 30, 1 << 30);
    REPORTER_ASSERT(reporter, nullptr == SkCanvas::MakeRasterDirect(info, baseAddr, minRowBytes));

    // not a valid pixel type
    info = SkImageInfo::Make(10, 10, kUnknown_SkColorType, info.alphaType());
    REPORTER_ASSERT(reporter, nullptr == SkCanvas::MakeRasterDirect(info, baseAddr, minRowBytes));

    // We should succeed with a zero-sized valid info
    info = SkImageInfo::MakeN32Premul(0, 0);
    canvas = SkCanvas::MakeRasterDirect(info, baseAddr, minRowBytes);
    REPORTER_ASSERT(reporter, canvas);
}

   void setWHZ(int width, int height, int zoom) {
        fZoom = zoom;
        fBounds.set(0, 0, SkIntToScalar(width * zoom), SkIntToScalar(height * zoom));
        fMatrix.setScale(SkIntToScalar(zoom), SkIntToScalar(zoom));
        fInverse.setScale(SK_Scalar1 / zoom, SK_Scalar1 / zoom);
        fShader.reset(sk_tool_utils::create_checkerboard_shader(
                              0xFFCCCCCC, 0xFFFFFFFF, zoom));

        SkImageInfo info = SkImageInfo::MakeN32Premul(width, height);
        fMinSurface.reset(SkSurface::NewRaster(info));
        info = info.makeWH(width * zoom, height * zoom);
        fMaxSurface.reset(SkSurface::NewRaster(info));
    }

    bool getBitmapDeprecated(SkBitmap* result) const override {
        const SkImageInfo info = GrMakeInfoFromTexture(fTexture,
                                                       this->width(), this->height(),
                                                       this->isOpaque());
        if (!result->setInfo(info)) {
            return false;
        }

        const SkImageInfo prInfo = info.makeWH(fTexture->width(), fTexture->height());

        SkAutoTUnref<SkGrPixelRef> pixelRef(new SkGrPixelRef(prInfo, fTexture));
        result->setPixelRef(pixelRef, this->subset().fLeft, this->subset().fTop);
        return true;
    }

/*
 * Initiates the gif decode
 */
SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
                                        void* dst, size_t dstRowBytes,
                                        const Options& opts,
                                        SkPMColor* inputColorPtr,
                                        int* inputColorCount,
                                        int* rowsDecoded) {
    Result result = this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount, opts);
    if (kSuccess != result) {
        return result;
    }

    if (dstInfo.dimensions() != this->getInfo().dimensions()) {
        return gif_error("Scaling not supported.\n", kInvalidScale);
    }

    // Initialize the swizzler
    if (fFrameIsSubset) {
        const SkImageInfo subsetDstInfo = dstInfo.makeWH(fFrameRect.width(), fFrameRect.height());
        if (kSuccess != this->initializeSwizzler(subsetDstInfo, opts)) {
            return gif_error("Could not initialize swizzler.\n", kUnimplemented);
        }

        // Fill the background
        SkSampler::Fill(dstInfo, dst, dstRowBytes,
                this->getFillValue(dstInfo.colorType(), dstInfo.alphaType()),
                opts.fZeroInitialized);

        // Modify the dst pointer
        const int32_t dstBytesPerPixel = SkColorTypeBytesPerPixel(dstInfo.colorType());
        dst = SkTAddOffset<void*>(dst, dstRowBytes * fFrameRect.top() +
                dstBytesPerPixel * fFrameRect.left());
    } else {
        if (kSuccess != this->initializeSwizzler(dstInfo, opts)) {
            return gif_error("Could not initialize swizzler.\n", kUnimplemented);
        }
    }

    // Iterate over rows of the input
    uint32_t height = fFrameRect.height();
    for (uint32_t y = 0; y < height; y++) {
        if (!this->readRow()) {
            *rowsDecoded = y;
            return gif_error("Could not decode line.\n", kIncompleteInput);
        }
        void* dstRow = SkTAddOffset<void>(dst, dstRowBytes * this->outputScanline(y));
        fSwizzler->swizzle(dstRow, fSrcBuffer.get());
    }
    return kSuccess;
}

    void setWHZ(int width, int height, int zoom) {
        fW = width;
        fH = height;
        fZoom = zoom;
        fBounds.set(0, 0, SkIntToScalar(width * zoom), SkIntToScalar(height * zoom));
        fMatrix.setScale(SkIntToScalar(zoom), SkIntToScalar(zoom));
        fInverse.setScale(SK_Scalar1 / zoom, SK_Scalar1 / zoom);
        fShader0 = sk_tool_utils::create_checkerboard_shader(0xFFDDDDDD, 0xFFFFFFFF, zoom);
        fShader1 = SkShader::MakeColorShader(SK_ColorWHITE);
        fShader = fShader0;

        SkImageInfo info = SkImageInfo::MakeN32Premul(width, height);
        fMinSurface = SkSurface::MakeRaster(info);
        info = info.makeWH(width * zoom, height * zoom);
        fMaxSurface = SkSurface::MakeRaster(info);
    }

bool SkInstallDiscardablePixelRef(SkImageGenerator* generator, const SkIRect* subset, SkBitmap* dst,
                                  SkDiscardableMemory::Factory* factory) {
    SkAutoTDelete<SkImageGenerator> autoGenerator(generator);
    if (NULL == autoGenerator.get()) {
        return false;
    }

    SkImageInfo prInfo = autoGenerator->getInfo();
    if (prInfo.isEmpty()) {
        return false;
    }

    SkIPoint origin = SkIPoint::Make(0, 0);
    SkImageInfo bmInfo = prInfo;
    if (subset) {
        const SkIRect prBounds = SkIRect::MakeWH(prInfo.width(), prInfo.height());
        if (subset->isEmpty() || !prBounds.contains(*subset)) {
            return false;
        }
        bmInfo = prInfo.makeWH(subset->width(), subset->height());
        origin.set(subset->x(), subset->y());
    }

    // must compute our desired rowBytes w.r.t. the pixelRef's dimensions, not ours, which may be
    // smaller.
    if (!dst->setInfo(bmInfo, prInfo.minRowBytes())) {
        return false;
    }

    // Since dst->setInfo() may have changed/fixed-up info, we check from the bitmap
    SkASSERT(dst->info().colorType() != kUnknown_SkColorType);

    if (dst->empty()) {  // Use a normal pixelref.
        return dst->tryAllocPixels();
    }
    SkAutoTUnref<SkDiscardablePixelRef> ref(
            new SkDiscardablePixelRef(prInfo, autoGenerator.detach(), dst->rowBytes(), factory));
    dst->setPixelRef(ref, origin.x(), origin.y());
    return true;
}

SkCodec::Result SkGifCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
        const SkCodec::Options& opts, SkPMColor inputColorPtr[], int* inputColorCount) {

    Result result = this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount, this->options());
    if (kSuccess != result) {
        return result;
    }

    // Initialize the swizzler
    if (fFrameIsSubset) {
        const SkImageInfo subsetDstInfo = dstInfo.makeWH(fFrameRect.width(), fFrameRect.height());
        if (kSuccess != this->initializeSwizzler(subsetDstInfo, opts)) {
            return gif_error("Could not initialize swizzler.\n", kUnimplemented);
        }
    } else {
        if (kSuccess != this->initializeSwizzler(dstInfo, opts)) {
            return gif_error("Could not initialize swizzler.\n", kUnimplemented);
        }
    }

    return kSuccess;
}

void SubsetSingleBench::onDraw(const int n, SkCanvas* canvas) {
    // When the color type is kIndex8, we will need to store the color table.  If it is
    // used, it will be initialized by the codec.
    int colorCount;
    SkPMColor colors[256];
    if (fUseCodec) {
        for (int count = 0; count < n; count++) {
            SkAutoTDelete<SkCodec> codec(SkCodec::NewFromStream(fStream->duplicate()));
            const SkImageInfo info = codec->getInfo().makeColorType(fColorType);
            SkAutoTDeleteArray<uint8_t> row(SkNEW_ARRAY(uint8_t, info.minRowBytes()));
            SkScanlineDecoder* scanlineDecoder = codec->getScanlineDecoder(
                    info, NULL, colors, &colorCount);

            SkBitmap bitmap;
            bitmap.allocPixels(info.makeWH(fSubsetWidth, fSubsetHeight));

            scanlineDecoder->skipScanlines(fOffsetTop);
            uint32_t bpp = info.bytesPerPixel();
            for (uint32_t y = 0; y < fSubsetHeight; y++) {
                scanlineDecoder->getScanlines(row.get(), 1, 0);
                memcpy(bitmap.getAddr(0, y), row.get() + fOffsetLeft * bpp,
                        fSubsetWidth * bpp);
            }
        }
    } else {
        for (int count = 0; count < n; count++) {
            SkAutoTDelete<SkImageDecoder> decoder(SkImageDecoder::Factory(fStream));
            int width, height;
            decoder->buildTileIndex(fStream->duplicate(), &width, &height);
            SkBitmap bitmap;
            SkIRect rect = SkIRect::MakeXYWH(fOffsetLeft, fOffsetTop, fSubsetWidth,
                    fSubsetHeight);
            decoder->decodeSubset(&bitmap, rect, fColorType);
        }
    }
}

void SubsetTranslateBench::onDraw(const int n, SkCanvas* canvas) {
    // When the color type is kIndex8, we will need to store the color table.  If it is
    // used, it will be initialized by the codec.
    int colorCount;
    SkPMColor colors[256];
    if (fUseCodec) {
        for (int count = 0; count < n; count++) {
            SkAutoTDelete<SkScanlineDecoder> scanlineDecoder(
                    SkScanlineDecoder::NewFromStream(fStream->duplicate()));
            const SkImageInfo info = scanlineDecoder->getInfo().makeColorType(fColorType);
            SkAutoTDeleteArray<uint8_t> row(new uint8_t[info.minRowBytes()]);
            scanlineDecoder->start(info, nullptr, colors, &colorCount);

            SkBitmap bitmap;
            // Note that we use the same bitmap for all of the subsets.
            // It might be larger than necessary for the end subsets.
            SkImageInfo subsetInfo = info.makeWH(fSubsetWidth, fSubsetHeight);
            alloc_pixels(&bitmap, subsetInfo, colors, colorCount);

            for (int x = 0; x < info.width(); x += fSubsetWidth) {
                for (int y = 0; y < info.height(); y += fSubsetHeight) {
                    scanlineDecoder->skipScanlines(y);
                    const uint32_t currSubsetWidth =
                            x + (int) fSubsetWidth > info.width() ?
                            info.width() - x : fSubsetWidth;
                    const uint32_t currSubsetHeight =
                            y + (int) fSubsetHeight > info.height() ?
                            info.height() - y : fSubsetHeight;
                    const uint32_t bpp = info.bytesPerPixel();
                    for (uint32_t y = 0; y < currSubsetHeight; y++) {
                        scanlineDecoder->getScanlines(row.get(), 1, 0);
                        memcpy(bitmap.getAddr(0, y), row.get() + x * bpp,
                                currSubsetWidth * bpp);
                    }
                }
            }
        }
    } else {
        // We create a color table here to satisfy allocPixels() when the output
        // type is kIndex8.  It's okay that this is uninitialized since we never
        // use it.
        SkColorTable* colorTable = new SkColorTable(colors, 0);
        for (int count = 0; count < n; count++) {
            int width, height;
            SkAutoTDelete<SkImageDecoder> decoder(SkImageDecoder::Factory(fStream));
            decoder->buildTileIndex(fStream->duplicate(), &width, &height);
            SkBitmap bitmap;
            // Note that we use the same bitmap for all of the subsets.
            // It might be larger than necessary for the end subsets.
            // If we do not include this step, decodeSubset() would allocate space
            // for the pixels automatically, but this would not allow us to reuse the
            // same bitmap as the other subsets.  We want to reuse the same bitmap
            // because it gives a more fair comparison with SkCodec and is a common
            // use case of BitmapRegionDecoder.
            bitmap.allocPixels(SkImageInfo::Make(fSubsetWidth, fSubsetHeight,
                    fColorType, kOpaque_SkAlphaType), nullptr, colorTable);

            for (int x = 0; x < width; x += fSubsetWidth) {
                for (int y = 0; y < height; y += fSubsetHeight) {
                    const uint32_t currSubsetWidth = x + (int) fSubsetWidth > width ?
                            width - x : fSubsetWidth;
                    const uint32_t currSubsetHeight = y + (int) fSubsetHeight > height ?
                            height - y : fSubsetHeight;
                    SkIRect rect = SkIRect::MakeXYWH(x, y, currSubsetWidth,
                            currSubsetHeight);
                    decoder->decodeSubset(&bitmap, rect, fColorType);
                }
            }
        }
    }
}