NAME
Array::Tour::Spiral  Return coordinates to take a spiral path.
SYNOPSIS
use Array::Tour::Spiral qw(:directions);
my $spiral = Array::Tour::Spiral>new(
dimensions => [5, 5],
counterclock => $counterclock,
corner_right => $corner_right,
corner_bottom => $corner_bottom
inward => $inward);
Creates the object with its attributes. The attributes are:
 dimensions

Set the size of the grid:
my $spath1 = Array::Tour::Spiral>new(dimensions => [16, 16]);
If the grid is going to be square, a single integer is sufficient:
my $spath1 = Array::Tour::Spiral>new(dimensions => 16);
 counterclock corner_bottom corner_right inward

Default values: 0. All are boolean values that affect the starting point and the direction of the spiral path. By default, the spiral is generated outwards from the center, using the upper left corner (if there is a choice), in a clockwise direction. See the Examples section to see what effects the different combinations produce.
PREREQUISITES
Perl 5.8 or later. This is the version of perl under which this module was developed.
DESCRIPTION
A simple iterator that will return the coordinates of the next cell if one were to tour a matrice's cells in a spiral path.
Spiral Object Methods
direction
$dir = $tour>direction()
Return the direction we just walked.
Overrides Array::Tour's direction() method.
next()
Returns an array reference to the next coordinates to use. Returns undef if there is no next cell to visit.
my $ctr = 1;
my $tour = Array::Tour::Spiral>new(dimensions => 64);
while (my $cref = $tour>next())
{
my($x_coord, $y_coord, $z_coord) = @{$cref};
$grid[$y_coord, $x_coord] = isprime($ctr++);
}
The above example generates Ulam's Spiral http://en.wikipedia.org/wiki/Ulam_spiral in the array @grid.
Overrides Array::Tour's next() method.
anti_spiral()
$larips = $spiral>anti_spiral();
Return a new object that follows the same path as the original object, reversing the inward/outward direction.
_set()
$self>_set(%parameters);
Override Array::Tour's _set() method for one that can handle
our parameters.
_set_inward()
$self>_set_inward();
Set the attributes knowing that the spiral path goes inward.
_set_outward()
$self>_set_outward();
Set the attributes knowing that the spiral path goes outward.
Example: A Spiral Tour of the Square
The four by four case demonstrates the different possible spiral arrangements. There are four possible central positions. By default, the spiral will begin in the top left corner, but the options corner_bottom
and corner_right
can force the starting point to a different corner of the square.
The results below show the results of the four different combinations of ($corner_bottom, $corner_right), traveling clockwise. The characters 'a' .. 'p' were drawn in order to show the path of the spiral:
(0,0) (0,1) (1,1) (1,0)
ghij pefg mnop jklm
fabk odah lcde ibcn
edcl ncbi kbaf hado
ponm mlkj jihg gfep
What if the grid is five by five? With both dimensions odd, there is no left/right or top/bottom corner. There are still four possible paths to take though, as shown using the characters 'a' .. 'y':
(0,0) (0,1) (1,1) (1,0)
uvwxy qrstu mnopq yjklm
tghij pefgv lcder xibcn
sfabk odahw kbafs whado
redcl ncbix jihgt vgfep
qponm mlkjy yxwvu utsrq
Even though there is only one center square, the spiral path takes the same starting direction as the spiral on the four by four square does.
Example: The Spiral Tour of the Rectangle
Some of our assumptions go awry if width does not equal height. If the shorter of the two dimensions is even, the starting corner does not always go where one expects. Here are some examples.
AUTHOR
John M. Gamble may be found at <jgamble@cpan.org>