#include <stdio.h> /* printf(), puts(), sprintf(), fflush() */

#include <stdlib.h> /* exit(), strtoul(), malloc() */

#include <sys/types.h> /* open() */

#include <sys/stat.h> /* open() */

#include <fcntl.h> /* open() */

#include <unistd.h> /* read(), write(), close() */

#include <string.h> /* strlen() */

#include <errno.h> /* EIO */

#ifdef _WIN32

# define PRIuSIZET "Iu"

# define PRIuOFFT "Id"

#else

# define PRIuSIZET "zu"

# define PRIuOFFT "zd"

#endif

__attribute__((noreturn))

void usage (char *argv0) {

printf("Usage: %s <input> <width> <height> <columns> <directory>\n\n",

argv0);

puts("\tinput \t...filename");

puts("\twidth \t...of a single tile");

puts("\theight \t...of a single tile");

puts("\tcolumns \tHow many tiles wide the input image is");

puts("\tdirectory\tAn output directory that will be filled with tiles");

puts("\t\t\tThis directory MUST ALREADY EXIST");

exit(0);

}

__attribute__((noreturn))

void fail (const char *msg) { /* report function failures */

perror(msg);

exit(1);

}

__attribute__((noreturn))

void die (char *msg, int err) { puts(msg); exit(-err); }

int main (int argc, char **argv) {

size_t width, height, columns, rows, rowlen, eof;

int inputfd, *outputfd;

char *outputfile, *buf;

if (4 > argc) { usage(argv[0]); }

inputfd = open(argv[1], O_RDONLY);

width = 3 * strtoul(argv[2], NULL, 10); /* 3 == sizeof(pixel) */

height = strtoul(argv[3], NULL, 10);

columns = strtoul(argv[4], NULL, 10);

outputfd = (int *)malloc(columns * sizeof(int));

outputfile = (char *)malloc(strlen(argv[5])

+ strlen("/row000col000.png\n"));

rowlen = width * columns;

buf = malloc(rowlen);

if (rowlen != read(inputfd, buf, rowlen))

die("read error when starting", EIO);

eof = rows = 0;

do {

for (int c = 0; c < columns; c++) {

sprintf(outputfile, "%s/row%03" PRIuSIZET "col%03d.rgb",

argv[5], rows, c);

outputfd[c] = open(outputfile, O_CREAT | O_WRONLY | O_TRUNC, 0644);

}

for (int y = 0; y < height; y++) {

for (size_t c = 0; c < columns; c++)

if (width != write(outputfd[c], buf + c * width, width))

die("write error", EIO);

eof = (rowlen != read(inputfd, buf, rowlen));

}

for (int c = 0; c < columns; c++) close(outputfd[c]);

rows++;

} while (!eof);

printf("tiled %" PRIuSIZET " rows\n", rows);

return 0;

}