src/codec/SkBmpRLECodec.cpp

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

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

/*
 * Creates an instance of the decoder
 * Called only by NewFromStream
 */
SkBmpRLECodec::SkBmpRLECodec(const SkImageInfo& info, SkStream* stream,
                             uint16_t bitsPerPixel, uint32_t numColors,
                             uint32_t bytesPerColor, uint32_t offset,
                             SkCodec::SkScanlineOrder rowOrder)
    : INHERITED(info, 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,
                                           SkPMColor* inputColorPtr,
                                           int* inputColorCount,
                                           int* rowsDecoded) {
    if (opts.fSubset) {
        // Subsets are not supported.
        return kUnimplemented;
    }
    if (!conversion_possible(dstInfo, this->getInfo())) {
        SkCodecPrintf("Error: cannot convert input type to output type.\n");
        return kInvalidConversion;
    }

    Result result = this->prepareToDecode(dstInfo, opts, inputColorPtr, inputColorCount);
    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(int* numColors) {
    // 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();
        if (nullptr != numColors) {
            // We set the number of colors to maxColors in order to ensure
            // safe memory accesses.  Otherwise, an invalid pixel could
            // access memory outside of our color table array.
            *numColors = maxColors;
        }
        // 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;
        SkAutoTDeleteArray<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
        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] = SkPackARGB32NoCheck(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 kN32_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 kN32_SkColorType: {
                SkPMColor* dstRow = SkTAddOffset<SkPMColor>(dst, row * (int) dstRowBytes);
                dstRow[dstX] = SkPackARGB32NoCheck(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::prepareToDecode(const SkImageInfo& dstInfo,
        const SkCodec::Options& options, SkPMColor inputColorPtr[], int* inputColorCount) {
    // 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;

    // 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(inputColorCount)) {
        SkCodecPrintf("Error: could not create color table.\n");
        return SkCodec::kInvalidInput;
    }

    // Copy the color table to the client if necessary
    copy_color_table(dstInfo, this->fColorTable, inputColorPtr, inputColorCount);

    // 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) {
    // Set RLE flags
    static const uint8_t RLE_ESCAPE = 0;
    static const uint8_t RLE_EOL = 0;
    static const uint8_t RLE_EOF = 1;
    static const uint8_t RLE_DELTA = 2;

    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.
    // Because of the need for transparent pixels, kN32 is the only color
    // type that makes sense for the destination format.
    SkASSERT(kN32_SkColorType == dstInfo.colorType());
    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;
        dst = SkTAddOffset<void>(dst, fLinesToSkip * dstRowBytes);
        fLinesToSkip = 0;
    } else {
        fLinesToSkip -= height;
        return height;
    }

    // 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--;
                            }
                            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;
}

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