gifimagedecoder.cpp

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    m_failed = !m_reader->decode(m_data->buffer(), query, haltAtFrame);
    
    if (m_failed) {
        delete m_reader;
        m_reader = 0;
    }
}

// Callbacks from the GIF reader.
void GIFImageDecoder::sizeNowAvailable(unsigned width, unsigned height)
{
    m_size = IntSize(width, height);
    m_sizeAvailable = true;
}

void GIFImageDecoder::decodingHalted(unsigned bytesLeft)
{
    m_reader->setReadOffset(m_data->size() - bytesLeft);
}

void GIFImageDecoder::initFrameBuffer(unsigned frameIndex)
{
    // Initialize the frame rect in our buffer.
    IntRect frameRect(m_reader->frameXOffset(), m_reader->frameYOffset(),
                      m_reader->frameWidth(), m_reader->frameHeight());

    // Make sure the frameRect doesn't extend past the bottom-right of the buffer.
    if (frameRect.right() > m_size.width())
        frameRect.setWidth(m_size.width() - m_reader->frameXOffset());
    if (frameRect.bottom() > m_size.height())
        frameRect.setHeight(m_size.height() - m_reader->frameYOffset());

    RGBA32Buffer* const buffer = &m_frameBufferCache[frameIndex];
    buffer->setRect(frameRect);
    
    if (frameIndex == 0) {
        // This is the first frame, so we're not relying on any previous data.
        prepEmptyFrameBuffer(buffer);
    } else {
        // The starting state for this frame depends on the previous frame's
        // disposal method.
        //
        // Frames that use the DisposeOverwritePrevious method are effectively
        // no-ops in terms of changing the starting state of a frame compared to
        // the starting state of the previous frame, so skip over them.  (If the
        // first frame specifies this method, it will get treated like
        // DisposeOverwriteBgcolor below and reset to a completely empty image.)
        const RGBA32Buffer* prevBuffer = &m_frameBufferCache[--frameIndex];
        ASSERT(prevBuffer->status() == RGBA32Buffer::FrameComplete);
        RGBA32Buffer::FrameDisposalMethod prevMethod =
            prevBuffer->disposalMethod();
        while ((frameIndex > 0) &&
                (prevMethod == RGBA32Buffer::DisposeOverwritePrevious)) {
            prevBuffer = &m_frameBufferCache[--frameIndex];
            prevMethod = prevBuffer->disposalMethod();
        }

        if ((prevMethod == RGBA32Buffer::DisposeNotSpecified) ||
                (prevMethod == RGBA32Buffer::DisposeKeep)) {
            // Preserve the last frame as the starting state for this frame.
            buffer->bytes() = prevBuffer->bytes();
            buffer->setHasAlpha(prevBuffer->hasAlpha());
        } else {
            // We want to clear the previous frame to transparent, without
            // affecting pixels in the image outside of the frame.
            const IntRect& prevRect = prevBuffer->rect();
            if ((frameIndex == 0) ||
                    prevRect.contains(IntRect(IntPoint(0, 0), m_size))) {
                // Clearing the first frame, or a frame the size of the whole
                // image, results in a completely empty image.
                prepEmptyFrameBuffer(buffer);
            } else {
              // Copy the whole previous buffer, then clear just its frame.
              buffer->bytes() = prevBuffer->bytes();
              buffer->setHasAlpha(prevBuffer->hasAlpha());
              for (int y = prevRect.y(); y < prevRect.bottom(); ++y) {
                  unsigned* const currentRow =
                      buffer->bytes().data() + (y * m_size.width());
                  for (int x = prevRect.x(); x < prevRect.right(); ++x)
                      buffer->setRGBA(*(currentRow + x), 0, 0, 0, 0);
              }
              if ((prevRect.width() > 0) && (prevRect.height() > 0))
                buffer->setHasAlpha(true);
            }
        }
    }

    // Update our status to be partially complete.
    buffer->setStatus(RGBA32Buffer::FramePartial);

    // Reset the alpha pixel tracker for this frame.
    m_currentBufferSawAlpha = false;
}

void GIFImageDecoder::prepEmptyFrameBuffer(RGBA32Buffer* buffer) const
{
    buffer->bytes().resize(m_size.width() * m_size.height());
    buffer->bytes().fill(0);
    buffer->setHasAlpha(true);
}

void GIFImageDecoder::haveDecodedRow(unsigned frameIndex,
                                     unsigned char* rowBuffer,   // Pointer to single scanline temporary buffer
                                     unsigned char* rowEnd,
                                     unsigned rowNumber,  // The row index
                                     unsigned repeatCount,  // How many times to repeat the row
                                     bool writeTransparentPixels)
{
    // Initialize the frame if necessary.
    RGBA32Buffer& buffer = m_frameBufferCache[frameIndex];
    if (buffer.status() == RGBA32Buffer::FrameEmpty)
        initFrameBuffer(frameIndex);

    // Do nothing for bogus data.
    if (rowBuffer == 0 || static_cast<int>(m_reader->frameYOffset() + rowNumber) >= m_size.height())
      return;

    unsigned colorMapSize;
    unsigned char* colorMap;
    m_reader->getColorMap(colorMap, colorMapSize);
    if (!colorMap)
        return;

    // The buffers that we draw are the entire image's width and height, so a final output frame is
    // width * height RGBA32 values in size.
    //
    // A single GIF frame, however, can be smaller than the entire image, i.e., it can represent some sub-rectangle
    // within the overall image.  The rows we are decoding are within this
    // sub-rectangle.  This means that if the GIF frame's sub-rectangle is (x,y,w,h) then row 0 is really row
    // y, and each row goes from x to x+w.
    unsigned dstPos = (m_reader->frameYOffset() + rowNumber) * m_size.width() + m_reader->frameXOffset();
    unsigned* dst = buffer.bytes().data() + dstPos;
    unsigned* dstEnd = dst + m_size.width() - m_reader->frameXOffset();
    unsigned* currDst = dst;
    unsigned char* currentRowByte = rowBuffer;
    
    while (currentRowByte != rowEnd && currDst < dstEnd) {
        if ((!m_reader->isTransparent() || *currentRowByte != m_reader->transparentPixel()) && *currentRowByte < colorMapSize) {
            unsigned colorIndex = *currentRowByte * 3;
            unsigned red = colorMap[colorIndex];
            unsigned green = colorMap[colorIndex + 1];
            unsigned blue = colorMap[colorIndex + 2];
            RGBA32Buffer::setRGBA(*currDst, red, green, blue, 255);
        } else {
            m_currentBufferSawAlpha = true;
            // We may or may not need to write transparent pixels to the buffer.
            // If we're compositing against a previous image, it's wrong, and if
            // we're writing atop a cleared, fully transparent buffer, it's
            // unnecessary; but if we're decoding an interlaced gif and
            // displaying it "Haeberli"-style, we must write these for passes
            // beyond the first, or the initial passes will "show through" the
            // later ones.
            if (writeTransparentPixels)
                RGBA32Buffer::setRGBA(*currDst, 0, 0, 0, 0);
        }
        currDst++;
        currentRowByte++;
    }

    if (repeatCount > 1) {
        // Copy the row |repeatCount|-1 times.
        unsigned num = currDst - dst;
        unsigned size = num * sizeof(unsigned);
        unsigned width = m_size.width();
        unsigned* end = buffer.bytes().data() + width * m_size.height();
        currDst = dst + width;
        for (unsigned i = 1; i < repeatCount; i++) {
            if (currDst + num > end) // Protect against a buffer overrun from a bogus repeatCount.
                break;
            memcpy(currDst, dst, size);
            currDst += width;
        }
    }

    // Our partial height is rowNumber + 1, e.g., row 2 is the 3rd row, so that's a height of 3.
    // Adding in repeatCount - 1 to rowNumber + 1 works out to just be rowNumber + repeatCount.
    buffer.ensureHeight(rowNumber + repeatCount);
}

void GIFImageDecoder::frameComplete(unsigned frameIndex, unsigned frameDuration, RGBA32Buffer::FrameDisposalMethod disposalMethod)
{
    // Initialize the frame if necessary.  Some GIFs insert do-nothing frames,
    // in which case we never reach haveDecodedRow() before getting here.
    RGBA32Buffer& buffer = m_frameBufferCache[frameIndex];
    if (buffer.status() == RGBA32Buffer::FrameEmpty)
        initFrameBuffer(frameIndex);

    buffer.ensureHeight(m_size.height());
    buffer.setStatus(RGBA32Buffer::FrameComplete);
    buffer.setDuration(frameDuration);
    buffer.setDisposalMethod(disposalMethod);

    if (!m_currentBufferSawAlpha) {
        // The whole frame was non-transparent, so it's possible that the entire
        // resulting buffer was non-transparent, and we can setHasAlpha(false).
        if (buffer.rect().contains(IntRect(IntPoint(0, 0), m_size))) {
            buffer.setHasAlpha(false);
        } else if (frameIndex > 0) {
            // Tricky case.  This frame does not have alpha only if everywhere
            // outside its rect doesn't have alpha.  To know whether this is
            // true, we check the start state of the frame -- if it doesn't have
            // alpha, we're safe.
            //
            // First skip over prior DisposeOverwritePrevious frames (since they
            // don't affect the start state of this frame) the same way we do in
            // initFrameBuffer().
            const RGBA32Buffer* prevBuffer = &m_frameBufferCache[--frameIndex];
            while ((frameIndex > 0) &&
                    (prevBuffer->disposalMethod() ==
                        RGBA32Buffer::DisposeOverwritePrevious))
                prevBuffer = &m_frameBufferCache[--frameIndex];

            // Now, if we're at a DisposeNotSpecified or DisposeKeep frame, then
            // we can say we have no alpha if that frame had no alpha.  But
            // since in initFrameBuffer() we already copied that frame's alpha
            // state into the current frame's, we need do nothing at all here.
            //
            // The only remaining case is a DisposeOverwriteBgcolor frame.  If
            // it had no alpha, and its rect is contained in the current frame's
            // rect, we know the current frame has no alpha.
            if ((prevBuffer->disposalMethod() ==
                    RGBA32Buffer::DisposeOverwriteBgcolor) &&
                    !prevBuffer->hasAlpha() &&
                    buffer.rect().contains(prevBuffer->rect()))
                buffer.setHasAlpha(false);
        }
    }
}

void GIFImageDecoder::gifComplete()
{
    if (m_reader)
        m_repetitionCount = m_reader->repetitionCount();
    delete m_reader;
    m_reader = 0;
}

}

#endif // PLATFORM(CAIRO)