#!/usr/bin/perl -w
# generate_interlaced_ppm.pl - Don Yang (uguu.org)
#
# Generate interlaced image for testing odd/even downsampling.
#
# 12/23/11

use strict;

sub write_even_scanline($)
{
   my ($y) = @_;

   for(my $x = 1; $x < 255; $x++)
   {
      print "$x $y $y 0 0 0 ";
   }
   print "255 $y $y\n";
}

sub write_odd_scanline($)
{
   my ($y) = @_;

   for(my $x = 255; $x > 1; $x--)
   {
      print "0 0 0 $y $x $y ";
   }
   print "0 0 0\n";
}


print "P3\n509 509\n255\n";
for(my $y = 1; $y < 255; $y++)
{
   write_even_scanline($y);
   write_odd_scanline($y);
}
write_even_scanline(255);