srand 42;
my $W = 1024;
my $H = 1024;
my $maxscore = 10;
my $Grid = [];
for(my $i=0;$i<$W;$i++){
  $Grid->[$i] = [(0)x$H];
  for(my $j=0;$j<$H;$j++){
    $Grid->[$i]->[$j] = $maxscore - int(rand(2*$maxscore+1))
  }
}
# now add a highscore to stand out for just 1 cell in each column
my $highscore = 21;
for(my $i=0;$i<$W;$i++){
  $Grid->[$i]->[int(rand($H))] = $highscore;
}