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

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #include "SkBmpRLECodec.h"
 #include "SkCodecPriv.h"
 #include "SkColorData.h"
 #include "SkStream.h"

 /*
  * Creates an instance of the decoder
  * Called only by NewFromStream
  */
 SkBmpRLECodec::SkBmpRLECodec(int width, int height, const SkEncodedInfo& info,
                              std::unique_ptr<SkStream> stream,
                              uint16_t bitsPerPixel, uint32_t numColors,
                              uint32_t bytesPerColor, uint32_t offset,
                              SkCodec::SkScanlineOrder rowOrder)
     : INHERITED(width, height, info, std::move(stream), bitsPerPixel, rowOrder)
     , fColorTable(nullptr)
     , fNumColors(numColors)
     , fBytesPerColor(bytesPerColor)
     , fOffset(offset)
     , fBytesBuffered(0)
     , fCurrRLEByte(0)
     , fSampleX(1)
 {}

 /*
  * Initiates the bitmap decode
  */
 SkCodec::Result SkBmpRLECodec::onGetPixels(const SkImageInfo& dstInfo,
                                            void* dst, size_t dstRowBytes,
                                            const Options& opts,
                                            int* rowsDecoded) {
     if (opts.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
     }

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

     // Perform the decode
     int rows = this->decodeRows(dstInfo, dst, dstRowBytes, opts);
     if (rows != dstInfo.height()) {
         // We set rowsDecoded equal to the height because the background has already
         // been filled.  RLE encodings sometimes skip pixels, so we always start by
         // filling the background.
         *rowsDecoded = dstInfo.height();
         return kIncompleteInput;
     }

     return kSuccess;
 }

 /*
  * Process the color table for the bmp input
  */
  bool SkBmpRLECodec::createColorTable(SkColorType dstColorType) {
     // Allocate memory for color table
     uint32_t colorBytes = 0;
     SkPMColor colorTable[256];
     if (this->bitsPerPixel() <= 8) {
         // Inform the caller of the number of colors
         uint32_t maxColors = 1 << this->bitsPerPixel();
         // Don't bother reading more than maxColors.
         const uint32_t numColorsToRead =
             fNumColors == 0 ? maxColors : SkTMin(fNumColors, maxColors);

         // Read the color table from the stream
         colorBytes = numColorsToRead * fBytesPerColor;
         std::unique_ptr<uint8_t[]> cBuffer(new uint8_t[colorBytes]);
         if (stream()->read(cBuffer.get(), colorBytes) != colorBytes) {
             SkCodecPrintf("Error: unable to read color table.\n");
             return false;
         }

         // Fill in the color table
         PackColorProc packARGB = choose_pack_color_proc(false, dstColorType);
         uint32_t i = 0;
         for (; i < numColorsToRead; i++) {
             uint8_t blue = get_byte(cBuffer.get(), i*fBytesPerColor);
             uint8_t green = get_byte(cBuffer.get(), i*fBytesPerColor + 1);
             uint8_t red = get_byte(cBuffer.get(), i*fBytesPerColor + 2);
             colorTable[i] = packARGB(0xFF, red, green, blue);
         }

         // To avoid segmentation faults on bad pixel data, fill the end of the
         // color table with black.  This is the same the behavior as the
         // chromium decoder.
         for (; i < maxColors; i++) {
             colorTable[i] = SkPackARGB32NoCheck(0xFF, 0, 0, 0);
         }

         // Set the color table
         fColorTable.reset(new SkColorTable(colorTable, maxColors));
     }

     // Check that we have not read past the pixel array offset
     if(fOffset < colorBytes) {
         // This may occur on OS 2.1 and other old versions where the color
         // table defaults to max size, and the bmp tries to use a smaller
         // color table.  This is invalid, and our decision is to indicate
         // an error, rather than try to guess the intended size of the
         // color table.
         SkCodecPrintf("Error: pixel data offset less than color table size.\n");
         return false;
     }

     // After reading the color table, skip to the start of the pixel array
     if (stream()->skip(fOffset - colorBytes) != fOffset - colorBytes) {
         SkCodecPrintf("Error: unable to skip to image data.\n");
         return false;
     }

     // Return true on success
     return true;
 }

 bool SkBmpRLECodec::initializeStreamBuffer() {
     fBytesBuffered = this->stream()->read(fStreamBuffer, kBufferSize);
     if (fBytesBuffered == 0) {
         SkCodecPrintf("Error: could not read RLE image data.\n");
         return false;
     }
     fCurrRLEByte = 0;
     return true;
 }

 /*
  * @return the number of bytes remaining in the stream buffer after
  *         attempting to read more bytes from the stream
  */
 size_t SkBmpRLECodec::checkForMoreData() {
     const size_t remainingBytes = fBytesBuffered - fCurrRLEByte;
     uint8_t* buffer = fStreamBuffer;

     // We will be reusing the same buffer, starting over from the beginning.
     // Move any remaining bytes to the start of the buffer.
     // We use memmove() instead of memcpy() because there is risk that the dst
     // and src memory will overlap in corrupt images.
     memmove(buffer, SkTAddOffset<uint8_t>(buffer, fCurrRLEByte), remainingBytes);

     // Adjust the buffer ptr to the start of the unfilled data.
     buffer += remainingBytes;

     // Try to read additional bytes from the stream.  There are fCurrRLEByte
     // bytes of additional space remaining in the buffer, assuming that we
     // have already copied remainingBytes to the start of the buffer.
     size_t additionalBytes = this->stream()->read(buffer, fCurrRLEByte);

     // Update counters and return the number of bytes we currently have
     // available.  We are at the start of the buffer again.
     fCurrRLEByte = 0;
     fBytesBuffered = remainingBytes + additionalBytes;
     return fBytesBuffered;
 }

 /*
  * Set an RLE pixel using the color table
  */
 void SkBmpRLECodec::setPixel(void* dst, size_t dstRowBytes,
                              const SkImageInfo& dstInfo, uint32_t x, uint32_t y,
                              uint8_t index) {
     if (dst && is_coord_necessary(x, fSampleX, dstInfo.width())) {
         // Set the row
         uint32_t row = this->getDstRow(y, dstInfo.height());

         // Set the pixel based on destination color type
         const int dstX = get_dst_coord(x, fSampleX);
         switch (dstInfo.colorType()) {
             case kRGBA_8888_SkColorType:
             case kBGRA_8888_SkColorType: {
                 SkPMColor* dstRow = SkTAddOffset<SkPMColor>(dst, row * (int) dstRowBytes);
                 dstRow[dstX] = fColorTable->operator[](index);
                 break;
             }
             case kRGB_565_SkColorType: {
                 uint16_t* dstRow = SkTAddOffset<uint16_t>(dst, row * (int) dstRowBytes);
                 dstRow[dstX] = SkPixel32ToPixel16(fColorTable->operator[](index));
                 break;
             }
             default:
                 // This case should not be reached.  We should catch an invalid
                 // color type when we check that the conversion is possible.
                 SkASSERT(false);
                 break;
         }
     }
 }

 /*
  * Set an RLE pixel from R, G, B values
  */
 void SkBmpRLECodec::setRGBPixel(void* dst, size_t dstRowBytes,
                                 const SkImageInfo& dstInfo, uint32_t x,
                                 uint32_t y, uint8_t red, uint8_t green,
                                 uint8_t blue) {
     if (dst && is_coord_necessary(x, fSampleX, dstInfo.width())) {
         // Set the row
         uint32_t row = this->getDstRow(y, dstInfo.height());

         // Set the pixel based on destination color type
         const int dstX = get_dst_coord(x, fSampleX);
         switch (dstInfo.colorType()) {
             case kRGBA_8888_SkColorType: {
                 SkPMColor* dstRow = SkTAddOffset<SkPMColor>(dst, row * (int) dstRowBytes);
                 dstRow[dstX] = SkPackARGB_as_RGBA(0xFF, red, green, blue);
                 break;
             }
             case kBGRA_8888_SkColorType: {
                 SkPMColor* dstRow = SkTAddOffset<SkPMColor>(dst, row * (int) dstRowBytes);
                 dstRow[dstX] = SkPackARGB_as_BGRA(0xFF, red, green, blue);
                 break;
             }
             case kRGB_565_SkColorType: {
                 uint16_t* dstRow = SkTAddOffset<uint16_t>(dst, row * (int) dstRowBytes);
                 dstRow[dstX] = SkPack888ToRGB16(red, green, blue);
                 break;
             }
             default:
                 // This case should not be reached.  We should catch an invalid
                 // color type when we check that the conversion is possible.
                 SkASSERT(false);
                 break;
         }
     }
 }

 SkCodec::Result SkBmpRLECodec::onPrepareToDecode(const SkImageInfo& dstInfo,
         const SkCodec::Options& options) {
     // FIXME: Support subsets for scanline decodes.
     if (options.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
     }

     // Reset fSampleX. If it needs to be a value other than 1, it will get modified by
     // the sampler.
     fSampleX = 1;
     fLinesToSkip = 0;

     SkColorType colorTableColorType = dstInfo.colorType();
     if (this->colorXform()) {
         // Just set a known colorType for the colorTable.  No need to actually transform
         // the colors in the colorTable.
         colorTableColorType = kBGRA_8888_SkColorType;
     }

     // Create the color table if necessary and prepare the stream for decode
     // Note that if it is non-NULL, inputColorCount will be modified
     if (!this->createColorTable(colorTableColorType)) {
         SkCodecPrintf("Error: could not create color table.\n");
         return SkCodec::kInvalidInput;
     }

     // Initialize a buffer for encoded RLE data
     if (!this->initializeStreamBuffer()) {
         SkCodecPrintf("Error: cannot initialize stream buffer.\n");
         return SkCodec::kInvalidInput;
     }

     return SkCodec::kSuccess;
 }

 /*
  * Performs the bitmap decoding for RLE input format
  * RLE decoding is performed all at once, rather than a one row at a time
  */
 int SkBmpRLECodec::decodeRows(const SkImageInfo& info, void* dst, size_t dstRowBytes,
         const Options& opts) {
     const int width = this->getInfo().width();
     int height = info.height();

     // Account for sampling.
     SkImageInfo dstInfo = info.makeWH(get_scaled_dimension(width, fSampleX), height);

     // Set the background as transparent.  Then, if the RLE code skips pixels,
     // the skipped pixels will be transparent.
     if (dst) {
         SkSampler::Fill(dstInfo, dst, dstRowBytes, SK_ColorTRANSPARENT, opts.fZeroInitialized);
     }

     // Adjust the height and the dst if the previous call to decodeRows() left us
     // with lines that need to be skipped.
     if (height > fLinesToSkip) {
         height -= fLinesToSkip;
         if (dst) {
             dst = SkTAddOffset<void>(dst, fLinesToSkip * dstRowBytes);
         }
         fLinesToSkip = 0;

         dstInfo = dstInfo.makeWH(dstInfo.width(), height);
     } else {
         fLinesToSkip -= height;
         return height;
     }

     void* decodeDst = dst;
     size_t decodeRowBytes = dstRowBytes;
     SkImageInfo decodeInfo = dstInfo;
     if (decodeDst) {
         if (this->colorXform()) {
             decodeInfo = decodeInfo.makeColorType(kXformSrcColorType);
             if (kRGBA_F16_SkColorType == dstInfo.colorType()) {
                 int count = height * dstInfo.width();
                 this->resetXformBuffer(count);
                 sk_bzero(this->xformBuffer(), count * sizeof(uint32_t));
                 decodeDst = this->xformBuffer();
                 decodeRowBytes = dstInfo.width() * sizeof(uint32_t);
             }
         }
     }

     int decodedHeight = this->decodeRLE(decodeInfo, decodeDst, decodeRowBytes);
     if (this->colorXform() && decodeDst) {
         for (int y = 0; y < decodedHeight; y++) {
             this->applyColorXform(dst, decodeDst, dstInfo.width());
             decodeDst = SkTAddOffset<void>(decodeDst, decodeRowBytes);
             dst = SkTAddOffset<void>(dst, dstRowBytes);
         }
     }

     return decodedHeight;
 }

 int SkBmpRLECodec::decodeRLE(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes) {
     // Use the original width to count the number of pixels in each row.
     const int width = this->getInfo().width();

     // This tells us the number of rows that we are meant to decode.
     const int height = dstInfo.height();

     // Set RLE flags
     constexpr uint8_t RLE_ESCAPE = 0;
     constexpr uint8_t RLE_EOL = 0;
     constexpr uint8_t RLE_EOF = 1;
     constexpr uint8_t RLE_DELTA = 2;

     // Destination parameters
     int x = 0;
     int y = 0;

     while (true) {
         // If we have reached a row that is beyond the requested height, we have
         // succeeded.
         if (y >= height) {
             // It would be better to check for the EOF marker before indicating
             // success, but we may be performing a scanline decode, which
             // would require us to stop before decoding the full height.
             return height;
         }

         // Every entry takes at least two bytes
         if ((int) fBytesBuffered - fCurrRLEByte < 2) {
             if (this->checkForMoreData() < 2) {
                 return y;
             }
         }

         // Read the next two bytes.  These bytes have different meanings
         // depending on their values.  In the first interpretation, the first
         // byte is an escape flag and the second byte indicates what special
         // task to perform.
         const uint8_t flag = fStreamBuffer[fCurrRLEByte++];
         const uint8_t task = fStreamBuffer[fCurrRLEByte++];

         // Perform decoding
         if (RLE_ESCAPE == flag) {
             switch (task) {
                 case RLE_EOL:
                     x = 0;
                     y++;
                     break;
                 case RLE_EOF:
                     return height;
                 case RLE_DELTA: {
                     // Two bytes are needed to specify delta
                     if ((int) fBytesBuffered - fCurrRLEByte < 2) {
                         if (this->checkForMoreData() < 2) {
                             return y;
                         }
                     }
                     // Modify x and y
                     const uint8_t dx = fStreamBuffer[fCurrRLEByte++];
                     const uint8_t dy = fStreamBuffer[fCurrRLEByte++];
                     x += dx;
                     y += dy;
                     if (x > width) {
                         SkCodecPrintf("Warning: invalid RLE input.\n");
                         return y - dy;
                     } else if (y > height) {
                         fLinesToSkip = y - height;
                         return height;
                     }
                     break;
                 }
                 default: {
                     // If task does not match any of the above signals, it
                     // indicates that we have a sequence of non-RLE pixels.
                     // Furthermore, the value of task is equal to the number
                     // of pixels to interpret.
                     uint8_t numPixels = task;
                     const size_t rowBytes = compute_row_bytes(numPixels,
                             this->bitsPerPixel());
                     // Abort if setting numPixels moves us off the edge of the
                     // image.
                     if (x + numPixels > width) {
                         SkCodecPrintf("Warning: invalid RLE input.\n");
                         return y;
                     }

                     // Also abort if there are not enough bytes
                     // remaining in the stream to set numPixels.

                     // At most, alignedRowBytes can be 255 (max uint8_t) *
                     // 3 (max bytes per pixel) + 1 (aligned) = 766. If
                     // fStreamBuffer was smaller than this,
                     // checkForMoreData would never succeed for some bmps.
                     static_assert(255 * 3 + 1 < kBufferSize,
                                   "kBufferSize needs to be larger!");
                     const size_t alignedRowBytes = SkAlign2(rowBytes);
                     if ((int) fBytesBuffered - fCurrRLEByte < alignedRowBytes) {
                         SkASSERT(alignedRowBytes < kBufferSize);
                         if (this->checkForMoreData() < alignedRowBytes) {
                             return y;
                         }
                     }
                     // Set numPixels number of pixels
                     while (numPixels > 0) {
                         switch(this->bitsPerPixel()) {
                             case 4: {
                                 SkASSERT(fCurrRLEByte < fBytesBuffered);
                                 uint8_t val = fStreamBuffer[fCurrRLEByte++];
                                 setPixel(dst, dstRowBytes, dstInfo, x++,
                                         y, val >> 4);
                                 numPixels--;
                                 if (numPixels != 0) {
                                     setPixel(dst, dstRowBytes, dstInfo,
                                             x++, y, val & 0xF);
                                     numPixels--;
                                 }
                                 break;
                             }
                             case 8:
                                 SkASSERT(fCurrRLEByte < fBytesBuffered);
                                 setPixel(dst, dstRowBytes, dstInfo, x++,
                                         y, fStreamBuffer[fCurrRLEByte++]);
                                 numPixels--;
                                 break;
                             case 24: {
                                 SkASSERT(fCurrRLEByte + 2 < fBytesBuffered);
                                 uint8_t blue = fStreamBuffer[fCurrRLEByte++];
                                 uint8_t green = fStreamBuffer[fCurrRLEByte++];
                                 uint8_t red = fStreamBuffer[fCurrRLEByte++];
                                 setRGBPixel(dst, dstRowBytes, dstInfo,
                                             x++, y, red, green, blue);
                                 numPixels--;
                                 break;
                             }
                             default:
                                 SkASSERT(false);
                                 return y;
                         }
                     }
                     // Skip a byte if necessary to maintain alignment
                     if (!SkIsAlign2(rowBytes)) {
                         fCurrRLEByte++;
                     }
                     break;
                 }
             }
         } else {
             // If the first byte read is not a flag, it indicates the number of
             // pixels to set in RLE mode.
             const uint8_t numPixels = flag;
             const int endX = SkTMin<int>(x + numPixels, width);

             if (24 == this->bitsPerPixel()) {
                 // In RLE24, the second byte read is part of the pixel color.
                 // There are two more required bytes to finish encoding the
                 // color.
                 if ((int) fBytesBuffered - fCurrRLEByte < 2) {
                     if (this->checkForMoreData() < 2) {
                         return y;
                     }
                 }

                 // Fill the pixels up to endX with the specified color
                 uint8_t blue = task;
                 uint8_t green = fStreamBuffer[fCurrRLEByte++];
                 uint8_t red = fStreamBuffer[fCurrRLEByte++];
                 while (x < endX) {
                     setRGBPixel(dst, dstRowBytes, dstInfo, x++, y, red, green, blue);
                 }
             } else {
                 // In RLE8 or RLE4, the second byte read gives the index in the
                 // color table to look up the pixel color.
                 // RLE8 has one color index that gets repeated
                 // RLE4 has two color indexes in the upper and lower 4 bits of
                 // the bytes, which are alternated
                 uint8_t indices[2] = { task, task };
                 if (4 == this->bitsPerPixel()) {
                     indices[0] >>= 4;
                     indices[1] &= 0xf;
                 }

                 // Set the indicated number of pixels
                 for (int which = 0; x < endX; x++) {
                     setPixel(dst, dstRowBytes, dstInfo, x, y, indices[which]);
                     which = !which;
                 }
             }
         }
     }
 }

 bool SkBmpRLECodec::skipRows(int count) {
     const SkImageInfo rowInfo = SkImageInfo::Make(this->getInfo().width(), count, kN32_SkColorType,
             kUnpremul_SkAlphaType);

     return count == this->decodeRows(rowInfo, nullptr, 0, this->options());
 }

 // FIXME: Make SkBmpRLECodec have no knowledge of sampling.
 //        Or it should do all sampling natively.
 //        It currently is a hybrid that needs to know what SkScaledCodec is doing.
 class SkBmpRLESampler : public SkSampler {
 public:
     SkBmpRLESampler(SkBmpRLECodec* codec)
         : fCodec(codec)
     {
         SkASSERT(fCodec);
     }

 private:
     int onSetSampleX(int sampleX) override {
         return fCodec->setSampleX(sampleX);
     }

     // Unowned pointer. fCodec will delete this class in its destructor.
     SkBmpRLECodec* fCodec;
 };

 SkSampler* SkBmpRLECodec::getSampler(bool /*createIfNecessary*/) {
     // We will always create an SkBmpRLESampler if one is requested.
     // This allows clients to always use the SkBmpRLESampler's
     // version of fill(), which does nothing since RLE decodes have
     // already filled pixel memory.  This seems fine, since creating
     // an SkBmpRLESampler is pretty inexpensive.
     if (!fSampler) {
         fSampler.reset(new SkBmpRLESampler(this));
     }

     return fSampler.get();
 }

 int SkBmpRLECodec::setSampleX(int sampleX){
     fSampleX = sampleX;
     return get_scaled_dimension(this->getInfo().width(), sampleX);
 }
	/*
	* 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 "SkBmpRLECodec.h"
	#include "SkCodecPriv.h"
	#include "SkColorData.h"
	#include "SkStream.h"

	/*
	* Creates an instance of the decoder
	* Called only by NewFromStream
	*/
	SkBmpRLECodec::SkBmpRLECodec(int width, int height, const SkEncodedInfo& info,
	std::unique_ptr<SkStream> stream,
	uint16_t bitsPerPixel, uint32_t numColors,
	uint32_t bytesPerColor, uint32_t offset,
	SkCodec::SkScanlineOrder rowOrder)
	: INHERITED(width, height, info, std::move(stream), bitsPerPixel, rowOrder)
	, fColorTable(nullptr)
	, fNumColors(numColors)
	, fBytesPerColor(bytesPerColor)
	, fOffset(offset)
	, fBytesBuffered(0)
	, fCurrRLEByte(0)
	, fSampleX(1)
	{}

	/*
	* Initiates the bitmap decode
	*/
	SkCodec::Result SkBmpRLECodec::onGetPixels(const SkImageInfo& dstInfo,
	void* dst, size_t dstRowBytes,
	const Options& opts,
	int* rowsDecoded) {
	if (opts.fSubset) {
	// Subsets are not supported.
	return kUnimplemented;
	}

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

	// Perform the decode
	int rows = this->decodeRows(dstInfo, dst, dstRowBytes, opts);
	if (rows != dstInfo.height()) {
	// We set rowsDecoded equal to the height because the background has already
	// been filled. RLE encodings sometimes skip pixels, so we always start by
	// filling the background.
	*rowsDecoded = dstInfo.height();
	return kIncompleteInput;
	}

	return kSuccess;
	}

	/*
	* Process the color table for the bmp input
	*/
	bool SkBmpRLECodec::createColorTable(SkColorType dstColorType) {
	// Allocate memory for color table
	uint32_t colorBytes = 0;
	SkPMColor colorTable[256];
	if (this->bitsPerPixel() <= 8) {
	// Inform the caller of the number of colors
	uint32_t maxColors = 1 << this->bitsPerPixel();
	// Don't bother reading more than maxColors.
	const uint32_t numColorsToRead =
	fNumColors == 0 ? maxColors : SkTMin(fNumColors, maxColors);

	// Read the color table from the stream
	colorBytes = numColorsToRead * fBytesPerColor;
	std::unique_ptr<uint8_t[]> cBuffer(new uint8_t[colorBytes]);
	if (stream()->read(cBuffer.get(), colorBytes) != colorBytes) {
	SkCodecPrintf("Error: unable to read color table.\n");
	return false;
	}

	// Fill in the color table
	PackColorProc packARGB = choose_pack_color_proc(false, dstColorType);
	uint32_t i = 0;
	for (; i < numColorsToRead; i++) {
	uint8_t blue = get_byte(cBuffer.get(), i*fBytesPerColor);
	uint8_t green = get_byte(cBuffer.get(), i*fBytesPerColor + 1);
	uint8_t red = get_byte(cBuffer.get(), i*fBytesPerColor + 2);
	colorTable[i] = packARGB(0xFF, red, green, blue);
	}

	// To avoid segmentation faults on bad pixel data, fill the end of the
	// color table with black. This is the same the behavior as the
	// chromium decoder.
	for (; i < maxColors; i++) {
	colorTable[i] = SkPackARGB32NoCheck(0xFF, 0, 0, 0);
	}

	// Set the color table
	fColorTable.reset(new SkColorTable(colorTable, maxColors));
	}

	// Check that we have not read past the pixel array offset
	if(fOffset < colorBytes) {
	// This may occur on OS 2.1 and other old versions where the color
	// table defaults to max size, and the bmp tries to use a smaller
	// color table. This is invalid, and our decision is to indicate
	// an error, rather than try to guess the intended size of the
	// color table.
	SkCodecPrintf("Error: pixel data offset less than color table size.\n");
	return false;
	}

	// After reading the color table, skip to the start of the pixel array
	if (stream()->skip(fOffset - colorBytes) != fOffset - colorBytes) {
	SkCodecPrintf("Error: unable to skip to image data.\n");
	return false;
	}

	// Return true on success
	return true;
	}

	bool SkBmpRLECodec::initializeStreamBuffer() {
	fBytesBuffered = this->stream()->read(fStreamBuffer, kBufferSize);
	if (fBytesBuffered == 0) {
	SkCodecPrintf("Error: could not read RLE image data.\n");
	return false;
	}
	fCurrRLEByte = 0;
	return true;
	}

	/*
	* @return the number of bytes remaining in the stream buffer after
	* attempting to read more bytes from the stream
	*/
	size_t SkBmpRLECodec::checkForMoreData() {
	const size_t remainingBytes = fBytesBuffered - fCurrRLEByte;
	uint8_t* buffer = fStreamBuffer;

	// We will be reusing the same buffer, starting over from the beginning.
	// Move any remaining bytes to the start of the buffer.
	// We use memmove() instead of memcpy() because there is risk that the dst
	// and src memory will overlap in corrupt images.
	memmove(buffer, SkTAddOffset<uint8_t>(buffer, fCurrRLEByte), remainingBytes);

	// Adjust the buffer ptr to the start of the unfilled data.
	buffer += remainingBytes;

	// Try to read additional bytes from the stream. There are fCurrRLEByte
	// bytes of additional space remaining in the buffer, assuming that we
	// have already copied remainingBytes to the start of the buffer.
	size_t additionalBytes = this->stream()->read(buffer, fCurrRLEByte);

	// Update counters and return the number of bytes we currently have
	// available. We are at the start of the buffer again.
	fCurrRLEByte = 0;
	fBytesBuffered = remainingBytes + additionalBytes;
	return fBytesBuffered;
	}

	/*
	* Set an RLE pixel using the color table
	*/
	void SkBmpRLECodec::setPixel(void* dst, size_t dstRowBytes,
	const SkImageInfo& dstInfo, uint32_t x, uint32_t y,
	uint8_t index) {
	if (dst && is_coord_necessary(x, fSampleX, dstInfo.width())) {
	// Set the row
	uint32_t row = this->getDstRow(y, dstInfo.height());

	// Set the pixel based on destination color type
	const int dstX = get_dst_coord(x, fSampleX);
	switch (dstInfo.colorType()) {
	case kRGBA_8888_SkColorType:
	case kBGRA_8888_SkColorType: {
	SkPMColor* dstRow = SkTAddOffset<SkPMColor>(dst, row * (int) dstRowBytes);
	dstRow[dstX] = fColorTable->operator[](index);
	break;
	}
	case kRGB_565_SkColorType: {
	uint16_t* dstRow = SkTAddOffset<uint16_t>(dst, row * (int) dstRowBytes);
	dstRow[dstX] = SkPixel32ToPixel16(fColorTable->operator[](index));
	break;
	}
	default:
	// This case should not be reached. We should catch an invalid
	// color type when we check that the conversion is possible.
	SkASSERT(false);
	break;
	}
	}
	}

	/*
	* Set an RLE pixel from R, G, B values
	*/
	void SkBmpRLECodec::setRGBPixel(void* dst, size_t dstRowBytes,
	const SkImageInfo& dstInfo, uint32_t x,
	uint32_t y, uint8_t red, uint8_t green,
	uint8_t blue) {
	if (dst && is_coord_necessary(x, fSampleX, dstInfo.width())) {
	// Set the row
	uint32_t row = this->getDstRow(y, dstInfo.height());

	// Set the pixel based on destination color type
	const int dstX = get_dst_coord(x, fSampleX);
	switch (dstInfo.colorType()) {
	case kRGBA_8888_SkColorType: {
	SkPMColor* dstRow = SkTAddOffset<SkPMColor>(dst, row * (int) dstRowBytes);
	dstRow[dstX] = SkPackARGB_as_RGBA(0xFF, red, green, blue);
	break;
	}
	case kBGRA_8888_SkColorType: {
	SkPMColor* dstRow = SkTAddOffset<SkPMColor>(dst, row * (int) dstRowBytes);
	dstRow[dstX] = SkPackARGB_as_BGRA(0xFF, red, green, blue);
	break;
	}
	case kRGB_565_SkColorType: {
	uint16_t* dstRow = SkTAddOffset<uint16_t>(dst, row * (int) dstRowBytes);
	dstRow[dstX] = SkPack888ToRGB16(red, green, blue);
	break;
	}
	default:
	// This case should not be reached. We should catch an invalid
	// color type when we check that the conversion is possible.
	SkASSERT(false);
	break;
	}
	}
	}

	SkCodec::Result SkBmpRLECodec::onPrepareToDecode(const SkImageInfo& dstInfo,
	const SkCodec::Options& options) {
	// FIXME: Support subsets for scanline decodes.
	if (options.fSubset) {
	// Subsets are not supported.
	return kUnimplemented;
	}

	// Reset fSampleX. If it needs to be a value other than 1, it will get modified by
	// the sampler.
	fSampleX = 1;
	fLinesToSkip = 0;

	SkColorType colorTableColorType = dstInfo.colorType();
	if (this->colorXform()) {
	// Just set a known colorType for the colorTable. No need to actually transform
	// the colors in the colorTable.
	colorTableColorType = kBGRA_8888_SkColorType;
	}

	// Create the color table if necessary and prepare the stream for decode
	// Note that if it is non-NULL, inputColorCount will be modified
	if (!this->createColorTable(colorTableColorType)) {
	SkCodecPrintf("Error: could not create color table.\n");
	return SkCodec::kInvalidInput;
	}

	// Initialize a buffer for encoded RLE data
	if (!this->initializeStreamBuffer()) {
	SkCodecPrintf("Error: cannot initialize stream buffer.\n");
	return SkCodec::kInvalidInput;
	}

	return SkCodec::kSuccess;
	}

	/*
	* Performs the bitmap decoding for RLE input format
	* RLE decoding is performed all at once, rather than a one row at a time
	*/
	int SkBmpRLECodec::decodeRows(const SkImageInfo& info, void* dst, size_t dstRowBytes,
	const Options& opts) {
	const int width = this->getInfo().width();
	int height = info.height();

	// Account for sampling.
	SkImageInfo dstInfo = info.makeWH(get_scaled_dimension(width, fSampleX), height);

	// Set the background as transparent. Then, if the RLE code skips pixels,
	// the skipped pixels will be transparent.
	if (dst) {
	SkSampler::Fill(dstInfo, dst, dstRowBytes, SK_ColorTRANSPARENT, opts.fZeroInitialized);
	}

	// Adjust the height and the dst if the previous call to decodeRows() left us
	// with lines that need to be skipped.
	if (height > fLinesToSkip) {
	height -= fLinesToSkip;
	if (dst) {
	dst = SkTAddOffset<void>(dst, fLinesToSkip * dstRowBytes);
	}
	fLinesToSkip = 0;

	dstInfo = dstInfo.makeWH(dstInfo.width(), height);
	} else {
	fLinesToSkip -= height;
	return height;
	}

	void* decodeDst = dst;
	size_t decodeRowBytes = dstRowBytes;
	SkImageInfo decodeInfo = dstInfo;
	if (decodeDst) {
	if (this->colorXform()) {
	decodeInfo = decodeInfo.makeColorType(kXformSrcColorType);
	if (kRGBA_F16_SkColorType == dstInfo.colorType()) {
	int count = height * dstInfo.width();
	this->resetXformBuffer(count);
	sk_bzero(this->xformBuffer(), count * sizeof(uint32_t));
	decodeDst = this->xformBuffer();
	decodeRowBytes = dstInfo.width() * sizeof(uint32_t);
	}
	}
	}

	int decodedHeight = this->decodeRLE(decodeInfo, decodeDst, decodeRowBytes);
	if (this->colorXform() && decodeDst) {
	for (int y = 0; y < decodedHeight; y++) {
	this->applyColorXform(dst, decodeDst, dstInfo.width());
	decodeDst = SkTAddOffset<void>(decodeDst, decodeRowBytes);
	dst = SkTAddOffset<void>(dst, dstRowBytes);
	}
	}

	return decodedHeight;
	}

	int SkBmpRLECodec::decodeRLE(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes) {
	// Use the original width to count the number of pixels in each row.
	const int width = this->getInfo().width();

	// This tells us the number of rows that we are meant to decode.
	const int height = dstInfo.height();

	// Set RLE flags
	constexpr uint8_t RLE_ESCAPE = 0;
	constexpr uint8_t RLE_EOL = 0;
	constexpr uint8_t RLE_EOF = 1;
	constexpr uint8_t RLE_DELTA = 2;

	// Destination parameters
	int x = 0;
	int y = 0;

	while (true) {
	// If we have reached a row that is beyond the requested height, we have
	// succeeded.
	if (y >= height) {
	// It would be better to check for the EOF marker before indicating
	// success, but we may be performing a scanline decode, which
	// would require us to stop before decoding the full height.
	return height;
	}

	// Every entry takes at least two bytes
	if ((int) fBytesBuffered - fCurrRLEByte < 2) {
	if (this->checkForMoreData() < 2) {
	return y;
	}
	}

	// Read the next two bytes. These bytes have different meanings
	// depending on their values. In the first interpretation, the first
	// byte is an escape flag and the second byte indicates what special
	// task to perform.
	const uint8_t flag = fStreamBuffer[fCurrRLEByte++];
	const uint8_t task = fStreamBuffer[fCurrRLEByte++];

	// Perform decoding
	if (RLE_ESCAPE == flag) {
	switch (task) {
	case RLE_EOL:
	x = 0;
	y++;
	break;
	case RLE_EOF:
	return height;
	case RLE_DELTA: {
	// Two bytes are needed to specify delta
	if ((int) fBytesBuffered - fCurrRLEByte < 2) {
	if (this->checkForMoreData() < 2) {
	return y;
	}
	}
	// Modify x and y
	const uint8_t dx = fStreamBuffer[fCurrRLEByte++];
	const uint8_t dy = fStreamBuffer[fCurrRLEByte++];
	x += dx;
	y += dy;
	if (x > width) {
	SkCodecPrintf("Warning: invalid RLE input.\n");
	return y - dy;
	} else if (y > height) {
	fLinesToSkip = y - height;
	return height;
	}
	break;
	}
	default: {
	// If task does not match any of the above signals, it
	// indicates that we have a sequence of non-RLE pixels.
	// Furthermore, the value of task is equal to the number
	// of pixels to interpret.
	uint8_t numPixels = task;
	const size_t rowBytes = compute_row_bytes(numPixels,
	this->bitsPerPixel());
	// Abort if setting numPixels moves us off the edge of the
	// image.
	if (x + numPixels > width) {
	SkCodecPrintf("Warning: invalid RLE input.\n");
	return y;
	}

	// Also abort if there are not enough bytes
	// remaining in the stream to set numPixels.

	// At most, alignedRowBytes can be 255 (max uint8_t) *
	// 3 (max bytes per pixel) + 1 (aligned) = 766. If
	// fStreamBuffer was smaller than this,
	// checkForMoreData would never succeed for some bmps.
	static_assert(255 * 3 + 1 < kBufferSize,
	"kBufferSize needs to be larger!");
	const size_t alignedRowBytes = SkAlign2(rowBytes);
	if ((int) fBytesBuffered - fCurrRLEByte < alignedRowBytes) {
	SkASSERT(alignedRowBytes < kBufferSize);
	if (this->checkForMoreData() < alignedRowBytes) {
	return y;
	}
	}
	// Set numPixels number of pixels
	while (numPixels > 0) {
	switch(this->bitsPerPixel()) {
	case 4: {
	SkASSERT(fCurrRLEByte < fBytesBuffered);
	uint8_t val = fStreamBuffer[fCurrRLEByte++];
	setPixel(dst, dstRowBytes, dstInfo, x++,
	y, val >> 4);
	numPixels--;
	if (numPixels != 0) {
	setPixel(dst, dstRowBytes, dstInfo,
	x++, y, val & 0xF);
	numPixels--;
	}
	break;
	}
	case 8:
	SkASSERT(fCurrRLEByte < fBytesBuffered);
	setPixel(dst, dstRowBytes, dstInfo, x++,
	y, fStreamBuffer[fCurrRLEByte++]);
	numPixels--;
	break;
	case 24: {
	SkASSERT(fCurrRLEByte + 2 < fBytesBuffered);
	uint8_t blue = fStreamBuffer[fCurrRLEByte++];
	uint8_t green = fStreamBuffer[fCurrRLEByte++];
	uint8_t red = fStreamBuffer[fCurrRLEByte++];
	setRGBPixel(dst, dstRowBytes, dstInfo,
	x++, y, red, green, blue);
	numPixels--;
	break;
	}
	default:
	SkASSERT(false);
	return y;
	}
	}
	// Skip a byte if necessary to maintain alignment
	if (!SkIsAlign2(rowBytes)) {
	fCurrRLEByte++;
	}
	break;
	}
	}
	} else {
	// If the first byte read is not a flag, it indicates the number of
	// pixels to set in RLE mode.
	const uint8_t numPixels = flag;
	const int endX = SkTMin<int>(x + numPixels, width);

	if (24 == this->bitsPerPixel()) {
	// In RLE24, the second byte read is part of the pixel color.
	// There are two more required bytes to finish encoding the
	// color.
	if ((int) fBytesBuffered - fCurrRLEByte < 2) {
	if (this->checkForMoreData() < 2) {
	return y;
	}
	}

	// Fill the pixels up to endX with the specified color
	uint8_t blue = task;
	uint8_t green = fStreamBuffer[fCurrRLEByte++];
	uint8_t red = fStreamBuffer[fCurrRLEByte++];
	while (x < endX) {
	setRGBPixel(dst, dstRowBytes, dstInfo, x++, y, red, green, blue);
	}
	} else {
	// In RLE8 or RLE4, the second byte read gives the index in the
	// color table to look up the pixel color.
	// RLE8 has one color index that gets repeated
	// RLE4 has two color indexes in the upper and lower 4 bits of
	// the bytes, which are alternated
	uint8_t indices[2] = { task, task };
	if (4 == this->bitsPerPixel()) {
	indices[0] >>= 4;
	indices[1] &= 0xf;
	}

	// Set the indicated number of pixels
	for (int which = 0; x < endX; x++) {
	setPixel(dst, dstRowBytes, dstInfo, x, y, indices[which]);
	which = !which;
	}
	}
	}
	}
	}

	bool SkBmpRLECodec::skipRows(int count) {
	const SkImageInfo rowInfo = SkImageInfo::Make(this->getInfo().width(), count, kN32_SkColorType,
	kUnpremul_SkAlphaType);

	return count == this->decodeRows(rowInfo, nullptr, 0, this->options());
	}

	// FIXME: Make SkBmpRLECodec have no knowledge of sampling.
	// Or it should do all sampling natively.
	// It currently is a hybrid that needs to know what SkScaledCodec is doing.
	class SkBmpRLESampler : public SkSampler {
	public:
	SkBmpRLESampler(SkBmpRLECodec* codec)
	: fCodec(codec)
	{
	SkASSERT(fCodec);
	}

	private:
	int onSetSampleX(int sampleX) override {
	return fCodec->setSampleX(sampleX);
	}

	// Unowned pointer. fCodec will delete this class in its destructor.
	SkBmpRLECodec* fCodec;
	};

	SkSampler* SkBmpRLECodec::getSampler(bool /createIfNecessary/) {
	// We will always create an SkBmpRLESampler if one is requested.
	// This allows clients to always use the SkBmpRLESampler's
	// version of fill(), which does nothing since RLE decodes have
	// already filled pixel memory. This seems fine, since creating
	// an SkBmpRLESampler is pretty inexpensive.
	if (!fSampler) {
	fSampler.reset(new SkBmpRLESampler(this));
	}

	return fSampler.get();
	}

	int SkBmpRLECodec::setSampleX(int sampleX){
	fSampleX = sampleX;
	return get_scaled_dimension(this->getInfo().width(), sampleX);
	}