=encoding utf8

=head1 NAME

Math::Polygon::Clip - frame a polygon in a square

=head1 INHERITANCE

 Math::Polygon::Clip
   is a Exporter

=head1 SYNOPSIS

 my @poly  = ( [1,2], [2,4], [5,7], [1, 2] );
 my @box   = ( $xmin, $ymin, $xmax, $ymax );

 my $boxed = polygon_clip \@box, @poly;

=head1 DESCRIPTION

Cut-off all parts of the polygon which are outside the box

=head1 FUNCTIONS

=over 4

=item B<polygon_fill_clip1>(ARRAY-$box, LIST-of-$points)

Clipping a polygon into rectangles can be done in various ways.
With this algorithm (which I designed myself, but may not be new), the
parts of the polygon which are outside the $box are mapped on the borders.
The polygon stays in one piece.

Returned is one list of points, which is cleaned from double points,
spikes and superfluous intermediate points.

=item B<polygon_fill_clip2>(ARRAY-$box, LIST-of-$points)

B<To be implemented>.  The polygon falls apart in fragments, which are not
connected: paths which are followed in two directions are removed.
This is required by some applications, like polygons used in geographical
context (country contours and such).

=item B<polygon_fill_clip3>( ARRAY-$box, $out-$poly, [$in-$polys] )

B<To be implemented>.  A surrounding polygon, with possible
inclussions.

=item B<polygon_line_clip>(ARRAY-$box, LIST-of-$points)

Returned is a list of ARRAYS (possibly 0 long) containing line pieces
from the input polygon (or line).

example: 

 my @points = ( [1,2], [2,3], [2,0], [1,-1], [1,2] );
 my @bbox   = ( 0, -2, 2, 2 );
 my @l      = polygon_line_clip \@bbox, @points;
 print scalar @l;      # 1, only one piece found
 my @first = @{$l[0]}; # first is [2,0], [1,-1], [1,2]

=back

=head1 SEE ALSO

This module is part of Math-Polygon distribution version 1.06,
built on July 16, 2017. Website: F<http://perl.overmeer.net/geo/>

=head1 LICENSE

Copyrights 2004-2017 by [Mark Overmeer]. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
See F<http://dev.perl.org/licenses/>