Revert of Delete SkImageDecoder

src/images/SkImageDecoder_libjpeg.cpp

 /*
  * Copyright 2007 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
+#include "SkImageDecoder.h"
 #include "SkImageEncoder.h"
 #include "SkJpegUtility.h"
 #include "SkColorPriv.h"
 #include "SkDither.h"
+#include "SkMSAN.h"
+#include "SkScaledBitmapSampler.h"
 #include "SkStream.h"
 #include "SkTemplates.h"
 #include "SkTime.h"
 #include "SkUtils.h"
 #include "SkRTConf.h"
 #include "SkRect.h"
 #include "SkCanvas.h"
 
 
 #include <stdio.h>
 extern "C" {
     #include "jpeglib.h"
     #include "jerror.h"
 }
 
-// These enable timing code that report milliseconds for an encoding
+// These enable timing code that report milliseconds for an encoding/decoding
 //#define TIME_ENCODE
+//#define TIME_DECODE
 
 // this enables our rgb->yuv code, which is faster than libjpeg on ARM
 #define WE_CONVERT_TO_YUV
 
+// If ANDROID_RGB is defined by in the jpeg headers it indicates that jpeg offers
+// support for two additional formats (1) JCS_RGBA_8888 and (2) JCS_RGB_565.
+
+#define DEFAULT_FOR_SUPPRESS_JPEG_IMAGE_DECODER_WARNINGS true
+#define DEFAULT_FOR_SUPPRESS_JPEG_IMAGE_DECODER_ERRORS true
+SK_CONF_DECLARE(bool, c_suppressJPEGImageDecoderWarnings,
+                "images.jpeg.suppressDecoderWarnings",
+                DEFAULT_FOR_SUPPRESS_JPEG_IMAGE_DECODER_WARNINGS,
+                "Suppress most JPG warnings when calling decode functions.");
+SK_CONF_DECLARE(bool, c_suppressJPEGImageDecoderErrors,
+                "images.jpeg.suppressDecoderErrors",
+                DEFAULT_FOR_SUPPRESS_JPEG_IMAGE_DECODER_ERRORS,
+                "Suppress most JPG error messages when decode "
+                "function fails.");
+
+//////////////////////////////////////////////////////////////////////////
+//////////////////////////////////////////////////////////////////////////
+
+static void do_nothing_emit_message(jpeg_common_struct*, int) {
+    /* do nothing */
+}
+static void do_nothing_output_message(j_common_ptr) {
+    /* do nothing */
+}
+
+static void initialize_info(jpeg_decompress_struct* cinfo, skjpeg_source_mgr* src_mgr) {
+    SkASSERT(cinfo != nullptr);
+    SkASSERT(src_mgr != nullptr);
+    jpeg_create_decompress(cinfo);
+    cinfo->src = src_mgr;
+    /* To suppress warnings with a SK_DEBUG binary, set the
+     * environment variable "skia_images_jpeg_suppressDecoderWarnings"
+     * to "true".  Inside a program that links to skia:
+     * SK_CONF_SET("images.jpeg.suppressDecoderWarnings", true); */
+    if (c_suppressJPEGImageDecoderWarnings) {
+        cinfo->err->emit_message = &do_nothing_emit_message;
+    }
+    /* To suppress error messages with a SK_DEBUG binary, set the
+     * environment variable "skia_images_jpeg_suppressDecoderErrors"
+     * to "true".  Inside a program that links to skia:
+     * SK_CONF_SET("images.jpeg.suppressDecoderErrors", true); */
+    if (c_suppressJPEGImageDecoderErrors) {
+        cinfo->err->output_message = &do_nothing_output_message;
+    }
+}
+
+class SkJPEGImageDecoder : public SkImageDecoder {
+public:
+
+    Format getFormat() const override {
+        return kJPEG_Format;
+    }
+
+protected:
+    Result onDecode(SkStream* stream, SkBitmap* bm, Mode) override;
+    bool onDecodeYUV8Planes(SkStream* stream, SkISize componentSizes[3],
+                            void* planes[3], size_t rowBytes[3],
+                            SkYUVColorSpace* colorSpace) override;
+
+private:
+
+    /**
+     *  Determine the appropriate bitmap colortype and out_color_space based on
+     *  both the preference of the caller and the jpeg_color_space on the
+     *  jpeg_decompress_struct passed in.
+     *  Must be called after jpeg_read_header.
+     */
+    SkColorType getBitmapColorType(jpeg_decompress_struct*);
+
+    typedef SkImageDecoder INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////
+
+/* Automatically clean up after throwing an exception */
+class JPEGAutoClean {
+public:
+    JPEGAutoClean(): cinfo_ptr(nullptr) {}
+    ~JPEGAutoClean() {
+        if (cinfo_ptr) {
+            jpeg_destroy_decompress(cinfo_ptr);
+        }
+    }
+    void set(jpeg_decompress_struct* info) {
+        cinfo_ptr = info;
+    }
+private:
+    jpeg_decompress_struct* cinfo_ptr;
+};
+
 ///////////////////////////////////////////////////////////////////////////////
 
+/*  If we need to better match the request, we might examine the image and
+     output dimensions, and determine if the downsampling jpeg provided is
+     not sufficient. If so, we can recompute a modified sampleSize value to
+     make up the difference.
+
+     To skip this additional scaling, just set sampleSize = 1; below.
+ */
+static int recompute_sampleSize(int sampleSize,
+                                const jpeg_decompress_struct& cinfo) {
+    return sampleSize * cinfo.output_width / cinfo.image_width;
+}
+
+static bool valid_output_dimensions(const jpeg_decompress_struct& cinfo) {
+    /* These are initialized to 0, so if they have non-zero values, we assume
+       they are "valid" (i.e. have been computed by libjpeg)
+     */
+    return 0 != cinfo.output_width && 0 != cinfo.output_height;
+}
+
+static bool skip_src_rows(jpeg_decompress_struct* cinfo, void* buffer, int count) {
+    for (int i = 0; i < count; i++) {
+        JSAMPLE* rowptr = (JSAMPLE*)buffer;
+        int row_count = jpeg_read_scanlines(cinfo, &rowptr, 1);
+        if (1 != row_count) {
+            return false;
+        }
+    }
+    return true;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+// This guy exists just to aid in debugging, as it allows debuggers to just
+// set a break-point in one place to see all error exists.
+static void print_jpeg_decoder_errors(const jpeg_decompress_struct& cinfo,
+                         int width, int height, const char caller[]) {
+    if (!(c_suppressJPEGImageDecoderErrors)) {
+        char buffer[JMSG_LENGTH_MAX];
+        cinfo.err->format_message((const j_common_ptr)&cinfo, buffer);
+        SkDebugf("libjpeg error %d <%s> from %s [%d %d]\n",
+                 cinfo.err->msg_code, buffer, caller, width, height);
+    }
+}
+
+static bool return_false(const jpeg_decompress_struct& cinfo,
+                         const char caller[]) {
+    print_jpeg_decoder_errors(cinfo, 0, 0, caller);
+    return false;
+}
+
+static SkImageDecoder::Result return_failure(const jpeg_decompress_struct& cinfo,
+                                             const SkBitmap& bm, const char caller[]) {
+    print_jpeg_decoder_errors(cinfo, bm.width(), bm.height(), caller);
+    return SkImageDecoder::kFailure;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+// Convert a scanline of CMYK samples to RGBX in place. Note that this
+// method moves the "scanline" pointer in its processing
+static void convert_CMYK_to_RGB(uint8_t* scanline, unsigned int width) {
+    // At this point we've received CMYK pixels from libjpeg. We
+    // perform a crude conversion to RGB (based on the formulae
+    // from easyrgb.com):
+    //  CMYK -> CMY
+    //    C = ( C * (1 - K) + K )      // for each CMY component
+    //  CMY -> RGB
+    //    R = ( 1 - C ) * 255          // for each RGB component
+    // Unfortunately we are seeing inverted CMYK so all the original terms
+    // are 1-. This yields:
+    //  CMYK -> CMY
+    //    C = ( (1-C) * (1 - (1-K) + (1-K) ) -> C = 1 - C*K
+    // The conversion from CMY->RGB remains the same
+    for (unsigned int x = 0; x < width; ++x, scanline += 4) {
+        scanline[0] = SkMulDiv255Round(scanline[0], scanline[3]);
+        scanline[1] = SkMulDiv255Round(scanline[1], scanline[3]);
+        scanline[2] = SkMulDiv255Round(scanline[2], scanline[3]);
+        scanline[3] = 255;
+    }
+}
+
+/**
+ *  Common code for setting the error manager.
+ */
+static void set_error_mgr(jpeg_decompress_struct* cinfo, skjpeg_error_mgr* errorManager) {
+    SkASSERT(cinfo != nullptr);
+    SkASSERT(errorManager != nullptr);
+    cinfo->err = jpeg_std_error(errorManager);
+    errorManager->error_exit = skjpeg_error_exit;
+}
+
+/**
+ * Common code for setting the dct method.
+ */
+static void set_dct_method(const SkImageDecoder& decoder, jpeg_decompress_struct* cinfo) {
+    SkASSERT(cinfo != nullptr);
+    cinfo->dct_method = JDCT_ISLOW;
+}
+
+SkColorType SkJPEGImageDecoder::getBitmapColorType(jpeg_decompress_struct* cinfo) {
+    SkASSERT(cinfo != nullptr);
+
+    SrcDepth srcDepth = k32Bit_SrcDepth;
+    if (JCS_GRAYSCALE == cinfo->jpeg_color_space) {
+        srcDepth = k8BitGray_SrcDepth;
+    }
+
+    SkColorType colorType = this->getPrefColorType(srcDepth, /*hasAlpha*/ false);
+    switch (colorType) {
+        case kAlpha_8_SkColorType:
+            // Only respect A8 colortype if the original is grayscale,
+            // in which case we will treat the grayscale as alpha
+            // values.
+            if (cinfo->jpeg_color_space != JCS_GRAYSCALE) {
+                colorType = kN32_SkColorType;
+            }
+            break;
+        case kN32_SkColorType:
+            // Fall through.
+        case kARGB_4444_SkColorType:
+            // Fall through.
+        case kRGB_565_SkColorType:
+            // These are acceptable destination colortypes.
+            break;
+        default:
+            // Force all other colortypes to 8888.
+            colorType = kN32_SkColorType;
+            break;
+    }
+
+    switch (cinfo->jpeg_color_space) {
+        case JCS_CMYK:
+            // Fall through.
+        case JCS_YCCK:
+            // libjpeg cannot convert from CMYK or YCCK to RGB - here we set up
+            // so libjpeg will give us CMYK samples back and we will later
+            // manually convert them to RGB
+            cinfo->out_color_space = JCS_CMYK;
+            break;
+        case JCS_GRAYSCALE:
+            if (kAlpha_8_SkColorType == colorType) {
+                cinfo->out_color_space = JCS_GRAYSCALE;
+                break;
+            }
+            // The data is JCS_GRAYSCALE, but the caller wants some sort of RGB
+            // colortype. Fall through to set to the default.
+        default:
+            cinfo->out_color_space = JCS_RGB;
+            break;
+    }
+    return colorType;
+}
+
+/**
+ *  Based on the colortype and dither mode, adjust out_color_space and
+ *  dither_mode of cinfo. Only does work in ANDROID_RGB
+ */
+static void adjust_out_color_space_and_dither(jpeg_decompress_struct* cinfo,
+                                              SkColorType colorType,
+                                              const SkImageDecoder& decoder) {
+    SkASSERT(cinfo != nullptr);
+#ifdef ANDROID_RGB
+    cinfo->dither_mode = JDITHER_NONE;
+    if (JCS_CMYK == cinfo->out_color_space) {
+        return;
+    }
+    switch (colorType) {
+        case kN32_SkColorType:
+            cinfo->out_color_space = JCS_RGBA_8888;
+            break;
+        case kRGB_565_SkColorType:
+            cinfo->out_color_space = JCS_RGB_565;
+            if (decoder.getDitherImage()) {
+                cinfo->dither_mode = JDITHER_ORDERED;
+            }
+            break;
+        default:
+            break;
+    }
+#endif
+}
+
+/**
+   Sets all pixels in given bitmap to SK_ColorWHITE for all rows >= y.
+   Used when decoding fails partway through reading scanlines to fill
+   remaining lines. */
+static void fill_below_level(int y, SkBitmap* bitmap) {
+    SkIRect rect = SkIRect::MakeLTRB(0, y, bitmap->width(), bitmap->height());
+    SkCanvas canvas(*bitmap);
+    canvas.clipRect(SkRect::Make(rect));
+    canvas.drawColor(SK_ColorWHITE);
+}
+
+/**
+ *  Get the config and bytes per pixel of the source data. Return
+ *  whether the data is supported.
+ */
+static bool get_src_config(const jpeg_decompress_struct& cinfo,
+                           SkScaledBitmapSampler::SrcConfig* sc,
+                           int* srcBytesPerPixel) {
+    SkASSERT(sc != nullptr && srcBytesPerPixel != nullptr);
+    if (JCS_CMYK == cinfo.out_color_space) {
+        // In this case we will manually convert the CMYK values to RGB
+        *sc = SkScaledBitmapSampler::kRGBX;
+        // The CMYK work-around relies on 4 components per pixel here
+        *srcBytesPerPixel = 4;
+    } else if (3 == cinfo.out_color_components && JCS_RGB == cinfo.out_color_space) {
+        *sc = SkScaledBitmapSampler::kRGB;
+        *srcBytesPerPixel = 3;
+#ifdef ANDROID_RGB
+    } else if (JCS_RGBA_8888 == cinfo.out_color_space) {
+        *sc = SkScaledBitmapSampler::kRGBX;
+        *srcBytesPerPixel = 4;
+    } else if (JCS_RGB_565 == cinfo.out_color_space) {
+        *sc = SkScaledBitmapSampler::kRGB_565;
+        *srcBytesPerPixel = 2;
+#endif
+    } else if (1 == cinfo.out_color_components &&
+               JCS_GRAYSCALE == cinfo.out_color_space) {
+        *sc = SkScaledBitmapSampler::kGray;
+        *srcBytesPerPixel = 1;
+    } else {
+        return false;
+    }
+    return true;
+}
+
+SkImageDecoder::Result SkJPEGImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode) {
+#ifdef TIME_DECODE
+    SkAutoTime atm("JPEG Decode");
+#endif
+
+    JPEGAutoClean autoClean;
+
+    jpeg_decompress_struct  cinfo;
+    skjpeg_source_mgr       srcManager(stream, this);
+
+    skjpeg_error_mgr errorManager;
+    set_error_mgr(&cinfo, &errorManager);
+
+    // All objects need to be instantiated before this setjmp call so that
+    // they will be cleaned up properly if an error occurs.
+    if (setjmp(errorManager.fJmpBuf)) {
+        return return_failure(cinfo, *bm, "setjmp");
+    }
+
+    initialize_info(&cinfo, &srcManager);
+    autoClean.set(&cinfo);
+
+    int status = jpeg_read_header(&cinfo, true);
+    if (status != JPEG_HEADER_OK) {
+        return return_failure(cinfo, *bm, "read_header");
+    }
+
+    /*  Try to fulfill the requested sampleSize. Since jpeg can do it (when it
+        can) much faster that we, just use their num/denom api to approximate
+        the size.
+    */
+    int sampleSize = this->getSampleSize();
+
+    set_dct_method(*this, &cinfo);
+
+    SkASSERT(1 == cinfo.scale_num);
+    cinfo.scale_denom = sampleSize;
+
+    const SkColorType colorType = this->getBitmapColorType(&cinfo);
+    const SkAlphaType alphaType = kAlpha_8_SkColorType == colorType ?
+                                      kPremul_SkAlphaType : kOpaque_SkAlphaType;
+
+    adjust_out_color_space_and_dither(&cinfo, colorType, *this);
+
+    if (1 == sampleSize && SkImageDecoder::kDecodeBounds_Mode == mode) {
+        // Assume an A8 bitmap is not opaque to avoid the check of each
+        // individual pixel. It is very unlikely to be opaque, since
+        // an opaque A8 bitmap would not be very interesting.
+        // Otherwise, a jpeg image is opaque.
+        bool success = bm->setInfo(SkImageInfo::Make(cinfo.image_width, cinfo.image_height,
+                                                     colorType, alphaType));
+        return success ? kSuccess : kFailure;
+    }
+
+    /*  image_width and image_height are the original dimensions, available
+        after jpeg_read_header(). To see the scaled dimensions, we have to call
+        jpeg_start_decompress(), and then read output_width and output_height.
+    */
+    if (!jpeg_start_decompress(&cinfo)) {
+        /*  If we failed here, we may still have enough information to return
+            to the caller if they just wanted (subsampled bounds). If sampleSize
+            was 1, then we would have already returned. Thus we just check if
+            we're in kDecodeBounds_Mode, and that we have valid output sizes.
+
+            One reason to fail here is that we have insufficient stream data
+            to complete the setup. However, output dimensions seem to get
+            computed very early, which is why this special check can pay off.
+         */
+        if (SkImageDecoder::kDecodeBounds_Mode == mode && valid_output_dimensions(cinfo)) {
+            SkScaledBitmapSampler smpl(cinfo.output_width, cinfo.output_height,
+                                       recompute_sampleSize(sampleSize, cinfo));
+            // Assume an A8 bitmap is not opaque to avoid the check of each
+            // individual pixel. It is very unlikely to be opaque, since
+            // an opaque A8 bitmap would not be very interesting.
+            // Otherwise, a jpeg image is opaque.
+            bool success = bm->setInfo(SkImageInfo::Make(smpl.scaledWidth(), smpl.scaledHeight(),
+                                                         colorType, alphaType));
+            return success ? kSuccess : kFailure;
+        } else {
+            return return_failure(cinfo, *bm, "start_decompress");
+        }
+    }
+    sampleSize = recompute_sampleSize(sampleSize, cinfo);
+
+    SkScaledBitmapSampler sampler(cinfo.output_width, cinfo.output_height, sampleSize);
+    // Assume an A8 bitmap is not opaque to avoid the check of each
+    // individual pixel. It is very unlikely to be opaque, since
+    // an opaque A8 bitmap would not be very interesting.
+    // Otherwise, a jpeg image is opaque.
+    bm->setInfo(SkImageInfo::Make(sampler.scaledWidth(), sampler.scaledHeight(),
+                                  colorType, alphaType));
+    if (SkImageDecoder::kDecodeBounds_Mode == mode) {
+        return kSuccess;
+    }
+    if (!this->allocPixelRef(bm, nullptr)) {
+        return return_failure(cinfo, *bm, "allocPixelRef");
+    }
+
+    SkAutoLockPixels alp(*bm);
+
+#ifdef ANDROID_RGB
+    /* short-circuit the SkScaledBitmapSampler when possible, as this gives
+       a significant performance boost.
+    */
+    if (sampleSize == 1 &&
+        ((kN32_SkColorType == colorType && cinfo.out_color_space == JCS_RGBA_8888) ||
+         (kRGB_565_SkColorType == colorType && cinfo.out_color_space == JCS_RGB_565)))
+    {
+        JSAMPLE* rowptr = (JSAMPLE*)bm->getPixels();
+        INT32 const bpr =  bm->rowBytes();
+
+        while (cinfo.output_scanline < cinfo.output_height) {
+            int row_count = jpeg_read_scanlines(&cinfo, &rowptr, 1);
+            if (0 == row_count) {
+                // if row_count == 0, then we didn't get a scanline,
+                // so return early.  We will return a partial image.
+                fill_below_level(cinfo.output_scanline, bm);
+                cinfo.output_scanline = cinfo.output_height;
+                jpeg_finish_decompress(&cinfo);
+                return kPartialSuccess;
+            }
+            if (this->shouldCancelDecode()) {
+                return return_failure(cinfo, *bm, "shouldCancelDecode");
+            }
+            rowptr += bpr;
+        }
+        jpeg_finish_decompress(&cinfo);
+        return kSuccess;
+    }
+#endif
+
+    // check for supported formats
+    SkScaledBitmapSampler::SrcConfig sc;
+    int srcBytesPerPixel;
+
+    if (!get_src_config(cinfo, &sc, &srcBytesPerPixel)) {
+        return return_failure(cinfo, *bm, "jpeg colorspace");
+    }
+
+    if (!sampler.begin(bm, sc, *this)) {
+        return return_failure(cinfo, *bm, "sampler.begin");
+    }
+
+    SkAutoTMalloc<uint8_t> srcStorage(cinfo.output_width * srcBytesPerPixel);
+    uint8_t* srcRow = srcStorage.get();
+
+    //  Possibly skip initial rows [sampler.srcY0]
+    if (!skip_src_rows(&cinfo, srcRow, sampler.srcY0())) {
+        return return_failure(cinfo, *bm, "skip rows");
+    }
+
+    // now loop through scanlines until y == bm->height() - 1
+    for (int y = 0;; y++) {
+        JSAMPLE* rowptr = (JSAMPLE*)srcRow;
+        int row_count = jpeg_read_scanlines(&cinfo, &rowptr, 1);
+        sk_msan_mark_initialized(srcRow, srcRow + cinfo.output_width * srcBytesPerPixel,
+                                 "skbug.com/4550");
+        if (0 == row_count) {
+            // if row_count == 0, then we didn't get a scanline,
+            // so return early.  We will return a partial image.
+            fill_below_level(y, bm);
+            cinfo.output_scanline = cinfo.output_height;
+            jpeg_finish_decompress(&cinfo);
+            return kPartialSuccess;
+        }
+        if (this->shouldCancelDecode()) {
+            return return_failure(cinfo, *bm, "shouldCancelDecode");
+        }
+
+        if (JCS_CMYK == cinfo.out_color_space) {
+            convert_CMYK_to_RGB(srcRow, cinfo.output_width);
+        }
+
+
+        sampler.next(srcRow);
+        if (bm->height() - 1 == y) {
+            // we're done
+            break;
+        }
+
+        if (!skip_src_rows(&cinfo, srcRow, sampler.srcDY() - 1)) {
+            return return_failure(cinfo, *bm, "skip rows");
+        }
+    }
+
+    // we formally skip the rest, so we don't get a complaint from libjpeg
+    if (!skip_src_rows(&cinfo, srcRow,
+                       cinfo.output_height - cinfo.output_scanline)) {
+        return return_failure(cinfo, *bm, "skip rows");
+    }
+    jpeg_finish_decompress(&cinfo);
+
+    return kSuccess;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+enum SizeType {
+    kSizeForMemoryAllocation_SizeType,
+    kActualSize_SizeType
+};
+
+static SkISize compute_yuv_size(const jpeg_decompress_struct& info, int component,
+                                SizeType sizeType) {
+    if (sizeType == kSizeForMemoryAllocation_SizeType) {
+        return SkISize::Make(info.cur_comp_info[component]->width_in_blocks * DCTSIZE,
+                             info.cur_comp_info[component]->height_in_blocks * DCTSIZE);
+    }
+    return SkISize::Make(info.cur_comp_info[component]->downsampled_width,
+                         info.cur_comp_info[component]->downsampled_height);
+}
+
+static bool appears_to_be_yuv(const jpeg_decompress_struct& info) {
+    return (info.jpeg_color_space == JCS_YCbCr)
+        && (DCTSIZE == 8)
+        && (info.num_components == 3)
+        && (info.comps_in_scan >= info.num_components)
+        && (info.scale_denom <= 8)
+        && (info.cur_comp_info[0])
+        && (info.cur_comp_info[1])
+        && (info.cur_comp_info[2])
+        && (info.cur_comp_info[1]->h_samp_factor == 1)
+        && (info.cur_comp_info[1]->v_samp_factor == 1)
+        && (info.cur_comp_info[2]->h_samp_factor == 1)
+        && (info.cur_comp_info[2]->v_samp_factor == 1);
+}
+
+static void update_components_sizes(const jpeg_decompress_struct& cinfo, SkISize componentSizes[3],
+                                    SizeType sizeType) {
+    SkASSERT(appears_to_be_yuv(cinfo));
+    for (int i = 0; i < 3; ++i) {
+        componentSizes[i] = compute_yuv_size(cinfo, i, sizeType);
+    }
+}
+
+static bool output_raw_data(jpeg_decompress_struct& cinfo, void* planes[3], size_t rowBytes[3]) {
+    SkASSERT(appears_to_be_yuv(cinfo));
+    // U size and V size have to be the same if we're calling output_raw_data()
+    SkISize uvSize = compute_yuv_size(cinfo, 1, kSizeForMemoryAllocation_SizeType);
+    SkASSERT(uvSize == compute_yuv_size(cinfo, 2, kSizeForMemoryAllocation_SizeType));
+
+    JSAMPARRAY bufferraw[3];
+    JSAMPROW bufferraw2[32];
+    bufferraw[0] = &bufferraw2[0]; // Y channel rows (8 or 16)
+    bufferraw[1] = &bufferraw2[16]; // U channel rows (8)
+    bufferraw[2] = &bufferraw2[24]; // V channel rows (8)
+    int yWidth = cinfo.output_width;
+    int yHeight = cinfo.output_height;
+    int yMaxH = yHeight - 1;
+    int v = cinfo.cur_comp_info[0]->v_samp_factor;
+    int uvMaxH = uvSize.height() - 1;
+    JSAMPROW outputY = static_cast<JSAMPROW>(planes[0]);
+    JSAMPROW outputU = static_cast<JSAMPROW>(planes[1]);
+    JSAMPROW outputV = static_cast<JSAMPROW>(planes[2]);
+    size_t rowBytesY = rowBytes[0];
+    size_t rowBytesU = rowBytes[1];
+    size_t rowBytesV = rowBytes[2];
+
+    int yScanlinesToRead = DCTSIZE * v;
+    SkAutoMalloc lastRowStorage(rowBytesY * 4);
+    JSAMPROW yLastRow = (JSAMPROW)lastRowStorage.get();
+    JSAMPROW uLastRow = yLastRow + rowBytesY;
+    JSAMPROW vLastRow = uLastRow + rowBytesY;
+    JSAMPROW dummyRow = vLastRow + rowBytesY;
+
+    while (cinfo.output_scanline < cinfo.output_height) {
+        // Request 8 or 16 scanlines: returns 0 or more scanlines.
+        bool hasYLastRow(false), hasUVLastRow(false);
+        // Assign 8 or 16 rows of memory to read the Y channel.
+        for (int i = 0; i < yScanlinesToRead; ++i) {
+            int scanline = (cinfo.output_scanline + i);
+            if (scanline < yMaxH) {
+                bufferraw2[i] = &outputY[scanline * rowBytesY];
+            } else if (scanline == yMaxH) {
+                bufferraw2[i] = yLastRow;
+                hasYLastRow = true;
+            } else {
+                bufferraw2[i] = dummyRow;
+            }
+        }
+        int scaledScanline = cinfo.output_scanline / v;
+        // Assign 8 rows of memory to read the U and V channels.
+        for (int i = 0; i < 8; ++i) {
+            int scanline = (scaledScanline + i);
+            if (scanline < uvMaxH) {
+                bufferraw2[16 + i] = &outputU[scanline * rowBytesU];
+                bufferraw2[24 + i] = &outputV[scanline * rowBytesV];
+            } else if (scanline == uvMaxH) {
+                bufferraw2[16 + i] = uLastRow;
+                bufferraw2[24 + i] = vLastRow;
+                hasUVLastRow = true;
+            } else {
+                bufferraw2[16 + i] = dummyRow;
+                bufferraw2[24 + i] = dummyRow;
+            }
+        }
+        JDIMENSION scanlinesRead = jpeg_read_raw_data(&cinfo, bufferraw, yScanlinesToRead);
+
+        if (scanlinesRead == 0) {
+            return false;
+        }
+
+        if (hasYLastRow) {
+            memcpy(&outputY[yMaxH * rowBytesY], yLastRow, yWidth);
+        }
+        if (hasUVLastRow) {
+            memcpy(&outputU[uvMaxH * rowBytesU], uLastRow, uvSize.width());
+            memcpy(&outputV[uvMaxH * rowBytesV], vLastRow, uvSize.width());
+        }
+    }
+
+    cinfo.output_scanline = SkMin32(cinfo.output_scanline, cinfo.output_height);
+
+    return true;
+}
+
+bool SkJPEGImageDecoder::onDecodeYUV8Planes(SkStream* stream, SkISize componentSizes[3],
+                                            void* planes[3], size_t rowBytes[3],
+                                            SkYUVColorSpace* colorSpace) {
+#ifdef TIME_DECODE
+    SkAutoTime atm("JPEG YUV8 Decode");
+#endif
+    if (this->getSampleSize() != 1) {
+        return false; // Resizing not supported
+    }
+
+    JPEGAutoClean autoClean;
+
+    jpeg_decompress_struct  cinfo;
+    skjpeg_source_mgr       srcManager(stream, this);
+
+    skjpeg_error_mgr errorManager;
+    set_error_mgr(&cinfo, &errorManager);
+
+    // All objects need to be instantiated before this setjmp call so that
+    // they will be cleaned up properly if an error occurs.
+    if (setjmp(errorManager.fJmpBuf)) {
+        return return_false(cinfo, "setjmp YUV8");
+    }
+
+    initialize_info(&cinfo, &srcManager);
+    autoClean.set(&cinfo);
+
+    int status = jpeg_read_header(&cinfo, true);
+    if (status != JPEG_HEADER_OK) {
+        return return_false(cinfo, "read_header YUV8");
+    }
+
+    if (!appears_to_be_yuv(cinfo)) {
+        // It's not an error to not be encoded in YUV, so no need to use return_false()
+        return false;
+    }
+
+    cinfo.out_color_space = JCS_YCbCr;
+    cinfo.raw_data_out = TRUE;
+
+    if (!planes || !planes[0] || !rowBytes || !rowBytes[0]) { // Compute size only
+        update_components_sizes(cinfo, componentSizes, kSizeForMemoryAllocation_SizeType);
+        return true;
+    }
+
+    set_dct_method(*this, &cinfo);
+
+    SkASSERT(1 == cinfo.scale_num);
+    cinfo.scale_denom = 1;
+
+#ifdef ANDROID_RGB
+    cinfo.dither_mode = JDITHER_NONE;
+#endif
+
+    /*  image_width and image_height are the original dimensions, available
+        after jpeg_read_header(). To see the scaled dimensions, we have to call
+        jpeg_start_decompress(), and then read output_width and output_height.
+    */
+    if (!jpeg_start_decompress(&cinfo)) {
+        return return_false(cinfo, "start_decompress YUV8");
+    }
+
+    // Seems like jpeg_start_decompress is updating our opinion of whether cinfo represents YUV.
+    // Again, not really an error.
+    if (!appears_to_be_yuv(cinfo)) {
+        return false;
+    }
+
+    if (!output_raw_data(cinfo, planes, rowBytes)) {
+        return return_false(cinfo, "output_raw_data");
+    }
+
+    update_components_sizes(cinfo, componentSizes, kActualSize_SizeType);
+    jpeg_finish_decompress(&cinfo);
+
+    if (nullptr != colorSpace) {
+        *colorSpace = kJPEG_SkYUVColorSpace;
+    }
+
+    return true;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
 #include "SkColorPriv.h"
 
 // taken from jcolor.c in libjpeg
 #if 0   // 16bit - precise but slow
     #define CYR     19595   // 0.299
     #define CYG     38470   // 0.587
     #define CYB      7471   // 0.114
 
     #define CUR    -11059   // -0.16874
     #define CUG    -21709   // -0.33126
@@ skipping 219 matching lines @@
         }
 
         jpeg_finish_compress(&cinfo);
         jpeg_destroy_compress(&cinfo);
 
         return true;
     }
 };
 
 ///////////////////////////////////////////////////////////////////////////////
+DEFINE_DECODER_CREATOR(JPEGImageDecoder);
 DEFINE_ENCODER_CREATOR(JPEGImageEncoder);
 ///////////////////////////////////////////////////////////////////////////////
 
+static bool is_jpeg(SkStreamRewindable* stream) {
+    static const unsigned char gHeader[] = { 0xFF, 0xD8, 0xFF };
+    static const size_t HEADER_SIZE = sizeof(gHeader);
+
+    char buffer[HEADER_SIZE];
+    size_t len = stream->read(buffer, HEADER_SIZE);
+
+    if (len != HEADER_SIZE) {
+        return false;   // can't read enough
+    }
+    if (memcmp(buffer, gHeader, HEADER_SIZE)) {
+        return false;
+    }
+    return true;
+}
+
+
+static SkImageDecoder* sk_libjpeg_dfactory(SkStreamRewindable* stream) {
+    if (is_jpeg(stream)) {
+        return new SkJPEGImageDecoder;
+    }
+    return nullptr;
+}
+
+static SkImageDecoder::Format get_format_jpeg(SkStreamRewindable* stream) {
+    if (is_jpeg(stream)) {
+        return SkImageDecoder::kJPEG_Format;
+    }
+    return SkImageDecoder::kUnknown_Format;
+}
+
 static SkImageEncoder* sk_libjpeg_efactory(SkImageEncoder::Type t) {
     return (SkImageEncoder::kJPEG_Type == t) ? new SkJPEGImageEncoder : nullptr;
 }
 
+static SkImageDecoder_DecodeReg gDReg(sk_libjpeg_dfactory);
+static SkImageDecoder_FormatReg gFormatReg(get_format_jpeg);
 static SkImageEncoder_EncodeReg gEReg(sk_libjpeg_efactory);