Function Adam7_getpassvalues

samples/shared/lodepng.cpp:3770–3796

Outputs various dimensions and positions in the image related to the Adam7 reduced images. passw: output containing the width of the 7 passes passh: output containing the height of the 7 passes filter_passstart: output containing the index of the start and end of each reduced image with filter bytes padded_passstart output containing the index of the start and end of each reduced image when with

 end at a full byte
*/
static void Adam7_getpassvalues(unsigned passw[7], unsigned passh[7], size_t filter_passstart[8],
                                size_t padded_passstart[8], size_t passstart[8], unsigned w, unsigned h, unsigned bpp)
{
  /*the passstart values have 8 values: the 8th one indicates the byte after the end of the 7th (= last) pass*/
  unsigned i;

  /*calculate width and height in pixels of each pass*/
  for(i = 0; i < 7; i++)
  {
    passw[i] = (w + ADAM7_DX[i] - ADAM7_IX[i] - 1) / ADAM7_DX[i];
    passh[i] = (h + ADAM7_DY[i] - ADAM7_IY[i] - 1) / ADAM7_DY[i];
    if(passw[i] == 0) passh[i] = 0;
    if(passh[i] == 0) passw[i] = 0;
  }

  filter_passstart[0] = padded_passstart[0] = passstart[0] = 0;
  for(i = 0; i < 7; i++)
  {
    /*if passw[i] is 0, it's 0 bytes, not 1 (no filtertype-byte)*/
    filter_passstart[i + 1] = filter_passstart[i]
                            + ((passw[i] && passh[i]) ? passh[i] * (1 + (passw[i] * bpp + 7) / 8) : 0);
    /*bits padded if needed to fill full byte at end of each scanline*/
    padded_passstart[i + 1] = padded_passstart[i] + passh[i] * ((passw[i] * bpp + 7) / 8);
    /*only padded at end of reduced image*/
    passstart[i + 1] = passstart[i] + (passh[i] * passw[i] * bpp + 7) / 8;
  }
}

#ifdef LODEPNG_COMPILE_DECODER