#!/usr/bin/perl -w
use strict;

# This takes two 2-dimensional points (A and B)
# and a width, and returns 4 points that are the
# counter-clockwise perimeter of a "thick line"
# (box) of the specified width around the line.

sub line2box
{
    my $w= pop @_;
    die 'Usage: line2box($ax,$ay,$bx,$by,$width)'
        if  $w <= 0  ||  4 != @_;
    # We just keep our 4 coordinates in a single array
    # so we don't have to repeat ourselves much below.

    $w /= 2;    # Length of offset vector is $width/2

    my @d;      # Differences between X and Y coord.s
    my $l= 0;
    for( 0, 1 ) {
        my $d= $_[$_] - $_[2+$_];
        $l += $d*$d;
        push @d, $d;
    }

    # Now $l is length**2, so we want to scale our
    # perpendicular vectors by $width / $length so:
    $l= sqrt( $w*$w / $l );
    $_ *= $l   for  @d;

    my @box;
    my @s= ( -1, 1 );   # Sign to apply (- or +)
    for my $s ( 0, 1 ) {         # Index into @s
        # $p==0 for A, $p==1 for B
        for my $p ( $s, !$s ) {  # Which point
            for my $c ( 0, 1 ) { # Which coordinate
                # Push the selected coordinate
                push @box,
                    $_[2*$p+$c] + $s[$s^$c]*$d[!$c];
            }
        }
    }
    return @box;
}

while(  <DATA>  ) {
    last if !/\S/;
    my @line= split ' ';
    $line[-1] **= 0.5;
    my @box= line2box( @line );
    printf qq[A line from A( %5.1f, %5.1f )$/]
        .  qq[       to   B( %5.1f, %5.1f )$/]
        .  qq[of width sqrt( %5.1f )$/]
        .  qq[is a box, counter-clock-wise:$/]
        .  qq[            W( %5.1f, %5.1f )$/]
        .  qq[            X( %5.1f, %5.1f )$/]
        .  qq[            Y( %5.1f, %5.1f )$/]
        .  qq[            Z( %5.1f, %5.1f )$/]
        .  $/
        ,  @line[0..3], $line[4]**2,
        ,  @box;
}