static int
read_header (FILE *fp, const char *magic, int *width, int *height,
int *maxval)
{
char m[3] = { 0 };
int ignored = fread (m, sizeof(m)-1, 1, fp);
if (strcmp(m, magic)) {
fprintf(stderr, "bad magic [%s]\n", m); return -1;
}
if (0 != skip_whitespace_and_comments(fp)) return -1;
if (1 != fscanf(fp, "%d", width)) return -1;
if (0 != skip_whitespace_and_comments(fp)) return -1;
if (1 != fscanf(fp, "%d", height)) return -1;
if (0 != skip_whitespace_and_comments(fp)) return -1;
if (1 != fscanf(fp, "%d", maxval)) return -1;
if (EOF == fgetc(fp)) return -1;
return 0;
}
int load_pnm_from_FILE(FILE *f, unsigned char ***pixels, int *width, int *height)
{
int maxval;
char type;
if (getc(f) != 'P')
{
fprintf(stderr, "PNM file not starts with 'P'\n");
exit(1);
}
type = getc(f);
skip_whitespace_and_comments(f);
switch(type)
{
case '4':
fscanf(f, "%d %d", width, height);
maxval = 255;
break;
case '5': case '6':
fscanf(f, "%d %d %d", width, height, &maxval);
break;
default:
fprintf(stderr, "only raw PNM files supported\n");
exit(1);
}
if (maxval != 255)
{
fprintf(stderr, "only 256-levels PNM supported\n");
exit(1);
}
switch(fgetc(f))
{
case ' ': case '\t': case '\r': case '\n':
break;
default:
fprintf(stderr, "corrupted PNM, current offset is %ld\n", ftell(f));
exit(1);
}
switch(type)
{
case '4':
*pixels = allocate_bitmap(*width, *height);
load_pbm_raster(f, *pixels, *width, *height);
return PBM;
case '5':
*pixels = allocate_bitmap(*width, *height);
fread(**pixels, *width, *height, f);
return PGM;
case '6':
*pixels = allocate_bitmap(*width * 3, *height);
fread(**pixels, *width * 3, *height, f);
return PPM;
default:
assert(0);
return 0;
}
}
