#!/usr/bin/env perl
# pnmjpegcrop - trim a pnm to 8 by 8, or whatever specified on cmd lin
+e
# created by stewart on 02002/10/25

# reads a whole PNM file from stdin into core, so a bit more of a
# hog than it should be. Writes suitably trimmed PNM stream to stdout.

use strict;
use warnings;
use integer;                    # hey, I actually use this here!

my $modulo=8;                   # real default
# scan arguments for something like -NN for default trim tile size
if ($#ARGV > -1) {
    if ($ARGV[0] =~ /^\-+[0-9]+/) {
        $modulo=shift(@ARGV);
        $modulo =~ s/\D+//g;
    }
}
$modulo=8 unless (defined($modulo)); # sanity checks
$modulo=1 if ($modulo < 1);     
my @file=<>;                    # slurp all input
my @pnminfo=();
# read pnm header; could use pnmfile(1) or identify(1) for this
# but since pnm is such a simple format ...
for (my $i=0; $i <=$#file; $i++) {
    $_=$file[$i];               # don't use foreach() as it modifies @
+file
    s/^\s+//;                   # clean leading w/s
    next if (m/^\#/);           # skip comments
    last if ($#pnminfo == 2);   # exit if we've read three things
    s/\s+$//;                   # normalize rest of w/s
    s/\s+/ /g;
    my @a=split(' ', $_);
    push @pnminfo, @a;
}
my ($type, $width, $height) = @pnminfo;
die "Input is not PNM\n" unless ($type =~ m/^P\d$/); # die on wrong in
+put
# tile mustn't be > width or height
($modulo)=sort {$a <=> $b} ($modulo, $width, $height);
my $iwidth=($width/$modulo)*$modulo; # these are integer divides, reme
+mber
my $iheight=($height/$modulo)*$modulo;
my $xoff=($width-$iwidth)/2;    # choose offset for as near centred as
+ we can
my $yoff=($height-$iheight)/2;

if (($width == $iwidth) and ($height == $iheight)) {
    # file already a multiple of $modulo x $modulo pixels, so leave it
+ alone
    print @file;                # splat whole file out to stdout
}
else {
    # use old-style pnmcut arguments so we're compatible
    # should probably be more careful with pnmcut path for non-trusted
+ use.
    open(PNMCUT, "| pnmcut $xoff $yoff $iwidth $iheight")
        or die "pnmcut failed: $!\n";
    print PNMCUT @file;         # splat whole file out through pnmcut
    close(PNMCUT);
}
exit;
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