Function WritePNG

xdevice.cpp:1173–1259

// that the PNG file produced will not be compressed any.

flag WritePNG(CONST Bitmap *b, FILE *file)
{
  dword rglCrc[256], crc, dwT, dwAdler;
  int n, k, ib = 0, x, y, s1 = 1, s2 = 0, i;
  byte rgbHead[13], *rgb;
  KV kv;

  // Initialize CRC table for chunk CRC's.
  for (n = 0; n < 256; n++) {
    crc = n;
    for (k = 0; k < 8; k++)
      crc = (crc & 1) ? (0xEDB88320L ^ (crc >> 1)) : (crc >> 1);
    rglCrc[n] = crc;
  }

  // PNG signature
  CONST byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
  fwrite(png_signature, 1, 8, file);

  // IHDR chunk
  dwT = LFlipB(b->x);
  CopyRgb((pbyte)&dwT, rgbHead, 4);
  dwT = LFlipB(b->y);
  CopyRgb((pbyte)&dwT, rgbHead + 4, 4);
  rgbHead[8]  = 8;  // Bit depth
  rgbHead[9]  = 2;  // Color type: Truecolor (RGB)
  rgbHead[10] = 0;  // Compression method
  rgbHead[11] = 0;  // Filter method
  rgbHead[12] = 0;  // Interlace method
  WritePNGChunk(file, "IHDR", rgbHead, 13, rglCrc);

  // Deflate block (no compression)
  int cbRow, cbDataBmp, cRowBlock, cBlock, iBlock, cbBlock;
  cbRow = b->x*cbPixelK + 1;
  cbDataBmp = cbRow * b->y;
  cRowBlock = 65535 / cbRow;
  cBlock = (b->y + (cRowBlock - 1)) / cRowBlock;

  rgb = PAllocate(2 + 5*cBlock + cbDataBmp + 4,
    "PNG data"); // zlib header + deflate + data + adler32
  if (rgb == NULL)
    return fFalse;
  rgb[ib++] = 0x78;  // Zlib header for no compression
  rgb[ib++] = 0x01;

  for (iBlock = 0; iBlock < cBlock; iBlock++) {
    // Uncompressed deflate block
    cbBlock = cbRow * ((iBlock+1)*cRowBlock <= b->y ? cRowBlock :
      b->y - iBlock*cRowBlock);
    rgb[ib++] = (iBlock >= cBlock-1);  // 0x1 for final block, no compression
    rgb[ib++] = cbBlock & 0xff;
    rgb[ib++] = (cbBlock >> 8) & 0xff;
    rgb[ib++] = ~cbBlock & 0xff;
    rgb[ib++] = (~cbBlock >> 8) & 0xff;

    for (y = iBlock*cRowBlock; y < (iBlock+1)*cRowBlock && y < b->y; y++) {
      rgb[ib++] = 0;
      for (x = 0; x < b->x; x++) {