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 } 66
