bool BMPImageReader::decodePixelData(bool nonRLE) {
const IntPoint coord(m_coord);
const ProcessingResult result =
nonRLE ? processNonRLEData(false, 0) : processRLEData();
if (m_coord != coord)
m_buffer->setPixelsChanged(true);
return (result == Failure) ? m_parent->setFailed() : (result == Success);
}
bool BMPImageReader::processRLEData()
{
if (m_decodedOffset > m_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 ((m_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 = m_data->data()[m_decodedOffset];
const uint8_t code = m_data->data()[m_decodedOffset + 1];
if ((count || (code != 1)) && pastEndOfImage(0))
return setFailed();
// Decode.
if (count == 0) {
switch (code) {
case 0: // Magic token: EOL
// Skip any remaining pixels in this row.
if (m_coord.x() < m_parent->size().width())
m_buffer->setHasAlpha(true);
moveBufferToNextRow();
m_decodedOffset += 2;
break;
case 1: // Magic token: EOF
// Skip any remaining pixels in the image.
if ((m_coord.x() < m_parent->size().width()) || (m_isTopDown ? (m_coord.y() < (m_parent->size().height() - 1)) : (m_coord.y() > 0)))
m_buffer->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 ((m_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 = m_data->data()[m_decodedOffset + 2];
const uint8_t dy = m_data->data()[m_decodedOffset + 3];
if (dx || dy)
m_buffer->setHasAlpha(true);
if (((m_coord.x() + dx) > m_parent->size().width()) || pastEndOfImage(dy))
return setFailed();
// 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(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, m_parent->size().width());
if (m_infoHeader.biCompression == RLE24) {
// Bail if there isn't enough data.
if ((m_data->size() - m_decodedOffset) < 4)
return false;
// One BGR triple that we copy |count| times.
fillRGBA(endX, m_data->data()[m_decodedOffset + 3], m_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))
return setFailed();
for (int which = 0; m_coord.x() < endX; ) {
setI(colorIndexes[which]);
which = !which;
}
m_decodedOffset += 2;
}
}
}