bmpimagereader.cpp

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    if ((m_decodedOffset > data->size())
        || ((data->size() - m_decodedOffset) < m_tableSizeInBytes))
        return false;
    m_colorTable.resize(m_infoHeader.biClrUsed);
    for (size_t i = 0; i < m_infoHeader.biClrUsed; ++i) {
        m_colorTable[i].rgbBlue = data->data()[m_decodedOffset++];
        m_colorTable[i].rgbGreen = data->data()[m_decodedOffset++];
        m_colorTable[i].rgbRed = data->data()[m_decodedOffset++];
        // Skip padding byte (not present on OS/2 1.x).
        if (!m_isOS21x)
            ++m_decodedOffset;
    }

    // We've now decoded all the non-image data we care about.  Skip anything
    // else before the actual raster data.
    if (m_imgDataOffset)
        m_decodedOffset = m_imgDataOffset;
    m_needToProcessColorTable = false;

    return true;
}

bool BMPImageReader::processRLEData(SharedBuffer* data)
{
    if (m_decodedOffset > data->size())
        return false;

    // RLE decoding is poorly specified.  Two main problems:
    // (1) Are EOL markers necessary?  What happens when we have too many
    //     pixels for one row?
    //     http://www.fileformat.info/format/bmp/egff.htm says extra pixels
    //     should wrap to the next line.  Real BMPs I've encountered seem to
    //     instead expect extra pixels to be ignored until the EOL marker is
    //     seen, although this has only happened in a few cases and I suspect
    //     those BMPs may be invalid.  So we only change lines on EOL (or Delta
    //     with dy > 0), and fail in most cases when pixels extend past the end
    //     of the line.
    // (2) When Delta, EOL, or EOF are seen, what happens to the "skipped"
    //     pixels?
    //     http://www.daubnet.com/formats/BMP.html says these should be filled
    //     with color 0.  However, the "do nothing" and "don't care" comments
    //     of other references suggest leaving these alone, i.e. letting them
    //     be transparent to the background behind the image.  This seems to
    //     match how MSPAINT treats BMPs, so we do that.  Note that when we
    //     actually skip pixels for a case like this, we need to note on the
    //     framebuffer that we have alpha.

    // Impossible to decode row-at-a-time, so just do things as a stream of
    // bytes.
    while (true) {
        // Every entry takes at least two bytes; bail if there isn't enough
        // data.
        if ((data->size() - m_decodedOffset) < 2)
            return false;

        // For every entry except EOF, we'd better not have reached the end of
        // the image.
        const uint8_t count = data->data()[m_decodedOffset];
        const uint8_t code = data->data()[m_decodedOffset + 1];
        if (((count != 0) || (code != 1)) && pastEndOfImage(0)) {
            m_failed = true;
            return false;
        }

        // Decode.
        if (count == 0) {
            switch (code) {
            case 0:  // Magic token: EOL
                // Skip any remaining pixels in this row.
                if (m_coord.x() < size().width())
                    m_frameBufferCache.first().setHasAlpha(true);
                moveBufferToNextRow();

                m_decodedOffset += 2;
                break;

            case 1:  // Magic token: EOF
                // Skip any remaining pixels in the image.
                if ((m_coord.x() < size().width())
                    || (m_isTopDown ? (m_coord.y() < (size().height() - 1)) : (m_coord.y() > 0)))
                    m_frameBufferCache.first().setHasAlpha(true);
                return true;

            case 2: {  // Magic token: Delta
                // The next two bytes specify dx and dy.  Bail if there isn't
                // enough data.
                if ((data->size() - m_decodedOffset) < 4)
                    return false;

                // Fail if this takes us past the end of the desired row or
                // past the end of the image.
                const uint8_t dx = data->data()[m_decodedOffset + 2];
                const uint8_t dy = data->data()[m_decodedOffset + 3];
                if ((dx != 0) || (dy != 0))
                    m_frameBufferCache.first().setHasAlpha(true);
                if (((m_coord.x() + dx) > size().width()) ||
                    pastEndOfImage(dy)) {
                    m_failed = true;
                    return false;
                }

                // Skip intervening pixels.
                m_coord.move(dx, m_isTopDown ? dy : -dy);

                m_decodedOffset += 4;
                break;
            }

            default:  // Absolute mode
                // |code| pixels specified as in BI_RGB, zero-padded at the end
                // to a multiple of 16 bits.
                // Because processNonRLEData() expects m_decodedOffset to
                // point to the beginning of the pixel data, bump it past
                // the escape bytes and then reset if decoding failed.
                m_decodedOffset += 2;
                if (!processNonRLEData(data, true, code)) {
                    m_decodedOffset -= 2;
                    return false;
                }
                break;
            }
        } else {  // Encoded mode
            // The following color data is repeated for |count| total pixels.
            // Strangely, some BMPs seem to specify excessively large counts
            // here; ignore pixels past the end of the row.
            const int endX = std::min(m_coord.x() + count, size().width());

            if (m_infoHeader.biCompression == RLE24) {
                // Bail if there isn't enough data.
                if ((data->size() - m_decodedOffset) < 4)
                    return false;

                // One BGR triple that we copy |count| times.
                fillRGBA(endX, data->data()[m_decodedOffset + 3],
                         data->data()[m_decodedOffset + 2], code, 0xff);
                m_decodedOffset += 4;
            } else {
                // RLE8 has one color index that gets repeated; RLE4 has two
                // color indexes in the upper and lower 4 bits of the byte,
                // which are alternated.
                size_t colorIndexes[2] = {code, code};
                if (m_infoHeader.biCompression == RLE4) {
                    colorIndexes[0] = (colorIndexes[0] >> 4) & 0xf;
                    colorIndexes[1] &= 0xf;
                }
                if ((colorIndexes[0] >= m_infoHeader.biClrUsed)
                    || (colorIndexes[1] >= m_infoHeader.biClrUsed)) {
                    m_failed = true;
                    return false;
                }
                for (int which = 0; m_coord.x() < endX; ) {
                    setI(colorIndexes[which]);
                    which = !which;
                }

                m_decodedOffset += 2;
            }
        }
    }
}

bool BMPImageReader::processNonRLEData(SharedBuffer* data, bool inRLE, int numPixels)
{
    if (m_decodedOffset > data->size())
        return false;

    if (!inRLE)
        numPixels = size().width();

    // Fail if we're being asked to decode more pixels than remain in the row.
    const int endX = m_coord.x() + numPixels;
    if (endX > size().width()) {
        m_failed = true;
        return false;
    }

    // Determine how many bytes of data the requested number of pixels
    // requires.
    const size_t pixelsPerByte = 8 / m_infoHeader.biBitCount;
    const size_t bytesPerPixel = m_infoHeader.biBitCount / 8;
    const size_t unpaddedNumBytes = (m_infoHeader.biBitCount < 16)
        ? ((numPixels + pixelsPerByte - 1) / pixelsPerByte)
        : (numPixels * bytesPerPixel);
    // RLE runs are zero-padded at the end to a multiple of 16 bits.  Non-RLE
    // data is in rows and is zero-padded to a multiple of 32 bits.
    const size_t alignBits = inRLE ? 1 : 3;
    const size_t paddedNumBytes = (unpaddedNumBytes + alignBits) & ~alignBits;

    // Decode as many rows as we can.  (For RLE, where we only want to decode
    // one row, we've already checked that this condition is true.)
    while (!pastEndOfImage(0)) {
        // Bail if we don't have enough data for the desired number of pixels.
        if ((data->size() - m_decodedOffset) < paddedNumBytes)
            return false;

        if (m_infoHeader.biBitCount < 16) {
            // Paletted data.  Pixels are stored little-endian within bytes.
            // Decode pixels one byte at a time, left to right (so, starting at
            // the most significant bits in the byte).
            const uint8_t mask = (1 << m_infoHeader.biBitCount) - 1;
            for (size_t byte = 0; byte < unpaddedNumBytes; ++byte) {
                uint8_t pixelData = data->data()[m_decodedOffset + byte];
                for (size_t pixel = 0; (pixel < pixelsPerByte) && (m_coord.x() < endX); ++pixel) {
                    const size_t colorIndex =
                        (pixelData >> (8 - m_infoHeader.biBitCount)) & mask;
                    if (m_andMaskState == Decoding) {
                        // There's no way to accurately represent an AND + XOR
                        // operation as an RGBA image, so where the AND values
                        // are 1, we simply set the framebuffer pixels to fully
                        // transparent, on the assumption that most ICOs on the
                        // web will not be doing a lot of inverting.
                        if (colorIndex) {
                            setRGBA(0, 0, 0, 0);
                            m_frameBufferCache.first().setHasAlpha(true);
                        } else
                            m_coord.move(1, 0);
                    } else {
                        if (colorIndex >= m_infoHeader.biClrUsed) {
                            m_failed = true;
                            return false;
                        }
                        setI(colorIndex);
                    }
                    pixelData <<= m_infoHeader.biBitCount;
                }
            }
        } else {
            // RGB data.  Decode pixels one at a time, left to right.
            while (m_coord.x() < endX) {
                const uint32_t pixel = readCurrentPixel(data, bytesPerPixel);

                // Some BMPs specify an alpha channel but don't actually use it
                // (it contains all 0s).  To avoid displaying these images as
                // fully-transparent, decode as if images are fully opaque
                // until we actually see a non-zero alpha value; at that point,
                // reset any previously-decoded pixels to fully transparent and
                // continue decoding based on the real alpha channel values.
                // As an optimization, avoid setting "hasAlpha" to true for
                // images where all alpha values are 255; opaque images are
                // faster to draw.
                int alpha = getAlpha(pixel);
                if (!m_seenNonZeroAlphaPixel && (alpha == 0)) {
                    m_seenZeroAlphaPixel = true;
                    alpha = 255;
                } else {
                    m_seenNonZeroAlphaPixel = true;
                    if (m_seenZeroAlphaPixel) {
                        // The eraseARGB() call here also sets "hasAlpha" true.
                        m_frameBufferCache.first().bitmap().eraseARGB(0, 0, 0,
                                                                      0);
                        m_seenZeroAlphaPixel = false;
                    } else if (alpha != 255)
                        m_frameBufferCache.first().setHasAlpha(true);
                }

                setRGBA(getComponent(pixel, 0), getComponent(pixel, 1),
                        getComponent(pixel, 2), alpha);
            }
        }

        // Success, keep going.
        m_decodedOffset += paddedNumBytes;
        if (inRLE)
            return true;
        moveBufferToNextRow();
    }

    // Finished decoding whole image.
    return true;
}

void BMPImageReader::moveBufferToNextRow()
{
    m_coord.move(-m_coord.x(), m_isTopDown ? 1 : -1);
}

} // namespace WebCore