explode.c

/* Compiling:
 *   $ gcc -O2 -o explode gifdec.c explode.c
 * Comparing gifdec with ImageMagick's GIF decoder:
 *   $ ./explode foo.gif      # generates gd_%03d.ppm files
 *   $ convert -coalesce foo.gif im_%03d.ppm
 *   $ # comparing entire animation:
 *   $ cat gd_*.ppm | md5sum
 *   $ cat im_*.ppm | md5sum
 *   $ # comparing each frame:
 *   $ md5sum gd_*.ppm
 *   $ md5sum im_*.ppm
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "gifdec.h"

int
main(int argc, char *argv[])
{
    gd_GIF *gif;
    int nframes = 0;
    char fname[0x10] = {0};
    uint8_t *image;
    FILE *fp;
    if (argc != 2) {
        fprintf(stderr, "usage:\n  %s input.gif\n", argv[0]);
        return 1;
    }
    gif = gd_open_gif(argv[1]);
    if (!gif) {
        fprintf(stderr, "could not read '%s'\n", argv[1]);
        return 1;
    }
    image = malloc(gif->width * gif->height * 3);
    if (!image) {
        fprintf(stderr, "could not allocate image buffer\n");
        return 1;
    }
    while (gd_get_frame(gif) == 1) {
        snprintf(fname, sizeof(fname) - 1, "gd_%03d.ppm", nframes);
        fp = fopen(fname, "w");
        fprintf(fp, "P6\n%d %d\n255\n", gif->width, gif->height);
        gd_render_frame(gif, image);
        fwrite(image, gif->width * gif->height, 3, fp);
        fclose(fp);
        nframes++;
    }
    gd_close_gif(gif);
    free(image);
    return 0;
}