1  /* Fake a PNG - just write it out directly.
       2   *
       3   * COPYRIGHT: Written by John Cunningham Bowler, 2014.
       4   * To the extent possible under law, the author has waived all copyright and
       5   * related or neighboring rights to this work.  This work is published from:
       6   * United States.
       7   *
       8   */
       9  
      10  #include <stdio.h>
      11  #include <zlib.h> /* for crc32 */
      12  
      13  void
      14  put_uLong(uLong val)
      15  {
      16     putchar(val >> 24);
      17     putchar(val >> 16);
      18     putchar(val >>  8);
      19     putchar(val >>  0);
      20  }
      21  
      22  void
      23  put_chunk(const unsigned char *chunk, uInt length)
      24  {
      25     uLong crc;
      26  
      27     put_uLong(length-4); /* Exclude the tag */
      28  
      29     fwrite(chunk, length, 1, stdout);
      30  
      31     crc = crc32(0, Z_NULL, 0);
      32     put_uLong(crc32(crc, chunk, length));
      33  }
      34  
      35  const unsigned char signature[] =
      36  {
      37     137, 80, 78, 71, 13, 10, 26, 10
      38  };
      39  
      40  const unsigned char IHDR[] =
      41  {
      42     73, 72, 68, 82, /* IHDR */
      43     0, 0, 0, 1, /* width */
      44     0, 0, 0, 1, /* height */
      45     1, /* bit depth */
      46     0, /* color type: greyscale */
      47     0, /* compression method */
      48     0, /* filter method */
      49     0  /* interlace method: none */
      50  };
      51  
      52  const unsigned char unknown[] =
      53  {
      54     'u', 'n', 'K', 'n' /* "unKn" - private safe to copy */
      55  };
      56  
      57  int
      58  main(void)
      59  {
      60     fwrite(signature, sizeof signature, 1, stdout);
      61     put_chunk(IHDR, sizeof IHDR);
      62  
      63     for (;;)
      64        put_chunk(unknown, sizeof unknown);
      65  }