I was trying to explain random-dot stereograms to a friend today, and wrote a little script that generates simple ASCII stereograms as a stepping stone along the way. The code isn't terribly exciting, but the whole 'scalars floating in space' thing is kinda pretty: 

    +            $step+         $step   +      $step      +
           $Co$W    $S    $Co$W    $S    $Co$W    $S    $Co$W
       $z           $L $z         $L   $z       $L     $z 
     $W     $L        $W     $L        $W     $L        $W
                                                          
    +                 +                 +                 +

[download]

The code (and a larger tableau) is below the fold. There's also a node about generating random-string stereograms from a height field here. 

    #!/usr/bin/perl
    
    use Strict;
    
    my $W = 18;     # column width
    my $H = 31;     # column height
    my $C =  3;     # number of column repeats
    my $L =  5;     # number of layers
    
    my $S =  4;     # step between items
    
    my @E = ();
    seek (DATA,0,0);
    
    for (<DATA>) {
        push @E, /(\$\w+)/g;    # harvest scalar names from the source
    }
    
    my @grid = (' 'x($W * $C))x$H;      #  build the basic array
    
    for my $i (0..$C) {                 #  add the registration marks
        for my $j (0..($#grid / 5)) {
            substr ($grid[ $j*5 ], $i*$W, 1) = '+';
        }
    }
    
    
    for my $layer (1..$L) {         #  add items from back to front
        my $step = $W - $layer;     #  set the offset for this layer
        
        for (my $z=0 ; $z < $H ; $z+=2+rand $S) {
            my $x = rand ($W);
            my $y = rand ($H);      # choose a random position/string
            my $e = $E[ rand @E ];
            
            for (my $pos=$x ; $pos<length($grid[$y]) ; $pos+=$step) {
                substr ($grid[$y], $pos, length $e) = $e;
            }
        }
    }
    
    print join ("\n", @grid), "\n";
    
    __DATA__

----- END OF FILE -----


    +$W            $W +          $W     +      $W         +
              $j               $j               $j        
                  $j              $j              $j      
    $grid         $$eid         $erid        $egrid       
                                                          
    +                 +                 +                 +
                   $pos         $posC        $pos  $C     
                                                          
                 $pos         $pos         $pos         $pos
     $H  $W $W     $W$H $W$W     $W  $H$$W     $W    $$W  
    +                 +                 +                 +
    $layer          $elayer      $e   $layer  $e       $lay$e
        $x         $j   $x         $j   $x         $j   $x
                                                          
              $pos         $pos         $pos         $pos 
    +             $pos+        $pos     +   $pos         $pos
                                                          
      $grid   $C    $grid    $C   $gridpos  $C  $grid  $pos
        $i            $i            $i            $i      
                                                          
    +            $step+         $step   +      $step      +
           $Co$W    $S    $Co$W    $S    $Co$W    $S    $Co$W
       $z           $L $z         $L   $z       $L     $z 
     $W     $L        $W     $L        $W     $L        $W
                                                          
    +                 +                 +                 +
           $z  $H$H       $z$H $H        $H  $H       $H$z
        $j$step $pos    $j $ste$pos$H   $j  $s$pos  $H  $j
                     $j               $j               $j 
               $W   $pos    $W      $pos $W         $p$W  
    +                 +                 +                 +

[download]

In reply to ASCII autostereograms by mstone

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