bool
SgiInput::read_native_scanline (int y, int z, void *data)
{
if (y < 0 || y > m_spec.height)
return false;
y = m_spec.height - y - 1;
int bpc = m_sgi_header.bpc;
std::vector<std::vector<unsigned char> > channeldata (m_spec.nchannels);
if (m_sgi_header.storage == sgi_pvt::RLE) {
// reading and uncompressing first channel (red in RGBA images)
for (int c = 0; c < m_spec.nchannels; ++c) {
int off = y + c*m_spec.height; // offset for this scanline/channel
int scanline_offset = start_tab[off];
int scanline_length = length_tab[off];
channeldata[c].resize (m_spec.width * bpc);
uncompress_rle_channel (scanline_offset, scanline_length,
&(channeldata[c][0]));
}
} else {
// non-RLE case -- just read directly into our channel data
for (int c = 0; c < m_spec.nchannels; ++c) {
int off = y + c*m_spec.height; // offset for this scanline/channel
int scanline_offset = sgi_pvt::SGI_HEADER_LEN + off * m_spec.width * bpc;
fseek (m_fd, scanline_offset, SEEK_SET);
channeldata[c].resize (m_spec.width * bpc);
if (! fread (&(channeldata[c][0]), 1, m_spec.width * bpc))
return false;
}
}
if (m_spec.nchannels == 1) {
// If just one channel, no interleaving is necessary, just memcpy
memcpy (data, &(channeldata[0][0]), channeldata[0].size());
} else {
unsigned char *cdata = (unsigned char *)data;
for (int x = 0; x < m_spec.width; ++x) {
for (int c = 0; c < m_spec.nchannels; ++c) {
*cdata++ = channeldata[c][x*bpc];
if (bpc == 2)
*cdata++ = channeldata[c][x*bpc+1];
}
}
}
// Swap endianness if needed
if (bpc == 2 && littleendian())
swap_endian ((unsigned short *)data, m_spec.width*m_spec.nchannels);
return true;
}
bool
SgiOutput::write_scanline (int y, int z, TypeDesc format, const void *data,
stride_t xstride)
{
y = m_spec.height - y - 1;
data = to_native_scanline (format, data, xstride, m_scratch,
m_dither, y, z);
// In SGI format all channels are saved to file separately: firsty all
// channel 1 scanlines are saved, then all channel2 scanlines are saved
// and so on.
//
// Note that since SGI images are pretty archaic and most probably
// people won't be too picky about full flexibility writing them, we
// content ourselves with only writing uncompressed data, and don't
// attempt to write with RLE encoding.
int bpc = m_spec.format.size(); // bytes per channel
std::vector<unsigned char> channeldata (m_spec.width * bpc);
for (int c = 0; c < m_spec.nchannels; ++c) {
unsigned char *cdata = (unsigned char *)data + c*bpc;
for (int x = 0; x < m_spec.width; ++x) {
channeldata[x*bpc] = cdata[0];
if (bpc == 2)
channeldata[x*bpc+1] = cdata[1];
cdata += m_spec.nchannels * bpc; // advance to next pixel
}
if (bpc == 2 && littleendian())
swap_endian ((unsigned short *)&channeldata[0], m_spec.width);
long scanline_offset = sgi_pvt::SGI_HEADER_LEN + (c * m_spec.height + y)
* m_spec.width * bpc;
fseek (m_fd, scanline_offset, SEEK_SET);
if (!fwrite (&channeldata[0], 1, m_spec.width * bpc)) {
return false;
}
}
return true;
}
