$canvas->Tk::bind("<Button-1>"        => \&start_mouse);
    $canvas->Tk::bind("<Motion>"          => \&move_mouse);
    $canvas->Tk::bind("<ButtonRelease-1>" => \&stop_mouse);

##</code><code>##


package Tk::Draw;

our $VERSION = '0.01';

=head1 NAME

Tk::Draw - Simplifies drawing with a mouse in a perl/Tk Canvas

=head1 DESCRIPTION

This module simplifies the drawing of perl/Tk shapes in a Canvas, using
a mouse.  Once the first <Button-N> event is detected for the given mouse
button N, and in the specified Canvas, the Motion and ButtonRelease events
are bound to the same mouse button and Canvas.  All subsequent points are
captured until the final ButtonRelease event occurs.  Finally, any previous
set bindings for the Canvas and mouse button are reinstated, and the
registered callback is invoked to handle any necessary final processing.

=head1 VERSION

Version 0.01

=head1 SYNOPSIS

use Tk::Draw;

Tk::Draw->new($canvas, \&final_callback, $h_args);

=head1 REQUIRED PARAMETERS

=over 4

=item $canvas

The Tk::Canvas object where the mouse events will be captured.

=item \&final_callback

A callback to invoked when the <ButtonRelease> event occurs.  The argument
is required, but may be a non-blank string (eg. 'none') if the user is
certain that no final processing is necessary.
(See the section FINAL CALLBACK below)

=item $h_args

An optional reference to a hash containing any of the following arguments:

=over 4

=item 'style'

The style of drawing to be done.  Must be one of:

=over 4

=item 'none'

Does not draw anything, just collects the (x,y) points generated by
moving the mouse over the canvas.

=item 'free'

Joins all points drawn to create freehand lines (this is the default).

=item 'line'

Joins the first point with the most recent point, to create a straight line.

=item 'oval'

Joins the first point with the most recent point to create an oval.

=item 'circle'

JOins the first point with the most recent point to create a circle.

=item 'rectangle'

JOins the first point with the most recent point to create a rectangle.

=item 'mouse'

The mouse button to bind the drawing to; one of {'1', '2' or '3'}.
The default is '1'.

=back

=item 'color'

The color of the object being drawn.  (Do not confuse this with the
'fill' argument).  The default color is 'black'.

=item 'fill'

The color with which to fill the drawn shape (does not apply to styles
'free' or 'line').  The default fill is '0' (ie. no fill).

=item 'width'

The width of the shape being draw.  In the case of lines (style 'free'
or 'line'), this referes to the line width; in all other shapes it is
the width of the shape's outline.  The default width is '1'.

=item 'action'

A callback to invoke each time a new point is detected.  It will be passed
a reference to an array containing the most recent (x, y) point detected,
eg. [ 123, 45 ].

=back

=back

=head1 FINAL CALLBACK

The final callback parameter names a subroutine to be invoked
when the mouse button is released.  This subroutine is passed the
following 3 arguments:

=over 4

$o_obj -- The Tk::Draw object

$a_points -- A reference to an array containing the captured coordinate
points, each of which is an array reference in the form [ x, y ]

$a_ids -- A reference to an array containing the ID(s) of the drawn shape

=back

=head1 METHODS

restart($obj, $h_args)

=over 4

Lets the user reuse the Tk::Draw object, optionally resetting any of
the same arguments as allowed to the new() method.  This method takes
the following 2 arguments:

=over 4

$obj

=over 4

The Tk::Draw object

=back

$h_args

=over 4

An optional hash, with the same values as allowed in the I<new()>
constructor.  (See the I<$h_args> parameter in the REQUIRED PARAMETERS
section above)

=back

=back

=back

transform($obj, $a_points, $xoff, $yoff, $canvas)

=over 4

Allows the recreation of the shape given by the points in $a_points to
an alternate location in the canvas (or in a separate canvas), and returns
the ID(s) associated with the new shape.  The following arguments are
required:

=over 4

$obj

=over 4

The Tk::Draw object.  The following accessor methods allow retrieval of
the corresponding member data:

=over 4

 $obj->canvas
 $obj->mouse
 $obj->color
 $obj->fill
 $obj->width
 $obj->style

=back

=back

$a_points

=over 4

A reference to an array containing the (x, y) points generated by an
initial call to Tk::Draw::new.  For example:

[ [10, 25], [12, 27], [13, 29], ... ]

=back

$xoff

=over 4

The x-offset by which to vary the new shape from the original

=back

$yoff

=over 4

The y-offset by which to vary the new shape from the original

=back

$canvas

=over 4

An optional Canvas on which to draw the new shape (it defaults to the
current Canvas used by $obj)

=back

=back

=back

=head1 EXAMPLE 1

=begin text

    #!/usr/bin/perl -w
    #
    # A very simple example of Tk::Draw, using each of the various
    # allowable styles.
    ##

    use strict;
    use warnings;
    use Tk;
    use Tk::Draw;

    my $a_style  = [qw[ free  line oval  circle rectangle ]];
    my $a_color  = [qw[ black red  blue  purple orange    ]];
    my $stylenum = 0;
    my $colornum = 0;

    my $mw    = new MainWindow(-title => 'Tk::Draw example');
    my $cv    = $mw->Canvas(-width  => 512, -height => 512)->pack;
    Tk::Draw->new($cv, \&done, { width => 5, fill => 'white' });
    MainLoop;

    # Tk::Draw final callback - change drawing style, and reinstall callback
    sub done {
        my ($o_obj, $a_points, $a_ids) = @_;
        my $style = $a_style->[++$stylenum % @$a_style];
        my $color = $a_color->[++$colornum % @$a_color];
        $o_obj->restart( { style => $style, color => $color });
    }
    
    
=end text

=head1 EXAMPLE 2

=begin text

    #!/usr/bin/perl -w
    #
    # A more complicated example of Tk::Draw, giving the user more
    # flexibility in choosing options to the constructor (although
    # the color and width are randomized).  This also demonstrates
    # usage of the -action => \&callback argument, to track points
    # as they are drawn, as well as showing the transform() method
    # which is used to make copies of the drawn object.
    ##

    use strict;
    use warnings;
    use Tk;
    use Tk::Draw;

    #############
    ## Globals ##
    #############
    my $a_styles = [qw[ free line oval circle rectangle ]];
    my $a_font   = [qw[ tahoma 12 ]];
    my @all_id1  = ( );
    my @all_id2  = ( );
    my $b_fill   = 0;
    my $lastxy   = "";
    my $style;

    ##################
    ## Main program ##
    ##################
    my $mw = new MainWindow(-title => 'Tk::Draw example');
    my $f1 = $mw->Frame()->pack(-fill => 'x');
    my $f2 = $mw->Frame()->pack(-fill => 'both');
    my $c1 = $f2->Canvas(-wi => 512,-he => 512, -bg => 'white');
    my $c2 = $f2->Canvas(-wi => 512,-he => 512, -bg => '#ffffdf');
    $c1->pack($c2, -side => 'left');

    button($f1, '>Quit (^Q)',          sub { exit }, 'Control-q');
    button($f1, '<Clear Last (space)', \&clear_last, 'space');
    button($f1, '<Clear All (Esc)',    \&clear_all,  'Escape');

    choose_style($f1);
    choose_fill($f1);
    last_point($f1);
    start_drawing($c1);
    MainLoop;

    #################
    ## Subroutines ##
    #################
    sub button {
        my ($w, $text, $c_cmd, $bind) = @_;
        my $side = ($text =~ s/^([<>])//)? $1: '<';
        my $bt = $w->Button(-bg => '#ffafef', -text => $text);
        $bt->configure(-comm => $c_cmd, -font => $a_font);
        if ($bind || 0) {
            $w->toplevel->bind("<$bind>" => sub { $bt->invoke });
        }
        $bt->pack(-side => ($side eq '<')? 'left': 'right');
    }

    sub random_color {
        sprintf "#%02x%02x%02x", rand(256), rand(256), rand(256);
    }

    sub clear_last {
        my $a_id1 = pop @all_id1;
        my $a_id2 = pop @all_id2;
        map { $c1->delete($_) } @$a_id1;
        map { $c2->delete($_) } @$a_id2;
    }

    sub clear_all {
        while (@all_id1 > 0) {
            clear_last();
        }
    }

    sub labeled_frame {
        my ($w, $text) = @_;
        my $fr = $w->Frame(-relief => 'ridge', -borderwidth => 4);
        my $lb = $fr->Label(-text  => $text, -font => $a_font);
        $fr->pack(-side => 'left');
        $lb->pack(-side => 'left');
        return $fr;
    }

    sub choose_style {
        my ($w) = @_;
        my $fr   = labeled_frame($w, "Style");
        my @args = (
            -bg       => '#7fcfff',
            -variable => \$style,
            -command  => \&start_drawing,
            -font     => $a_font,
        );
        my $opt = $fr->Optionmenu(@args);
        map { $opt->addOptions($_) } @$a_styles;
        $style = 'free';
        $opt->pack(-side => 'left');
    }

    sub choose_fill {
        my ($w) = @_;
        my $fr     = labeled_frame($w, "Fill Shapes");
        my $a_comm = [
            -font     => $a_font,
            -variable => \$b_fill,
            -command  => \&start_drawing,
        ];
        my $a_no   = [ -text => "No",  -value => 0 ];
        my $a_yes  = [ -text => "Yes", -value => 1 ];
        my $r_no   = $fr->Radiobutton(@$a_no,  @$a_comm);
        my $r_yes  = $fr->Radiobutton(@$a_yes, @$a_comm);
        $r_no->pack($r_yes, -side => 'left');
    }

    sub last_point {
        my ($w) = @_;
        my $fr  = labeled_frame($w, "Last Point");
        my $lbl = $fr->Label(-textvar => \$lastxy, -font => $a_font);
        $lbl->pack(-side => 'left');
    }

    #======================#
    ## Tk::Draw interface ##
    #======================#
    sub start_drawing {
        my $width = int(1 + rand(32));
        my $color = random_color();
        my $fill  = $b_fill? random_color: 0;

        my $h_opts = {
            'width'  => $width,
            'color'  => $color,
            'fill'   => $fill,
            'style'  => $style,
            'action' => \&show_last,
        };

        new Tk::Draw($c1, \&done_drawing, $h_opts);
    }

    sub show_last {
        my ($a_point) = @_;
        my ($x, $y) = @$a_point;
        $lastxy = sprintf "($x, $y)";
    }

    sub done_drawing {
        my ($o_obj, $a_points, $a_ids) = @_;
        push @all_id1, $a_ids;
        push @all_id2, Tk::Draw::transform($o_obj, $a_points, 0, 0, $c2);
        start_drawing();
    }
    

=end text

=head1 AUTHOR

John C. Norton

=head1 COPYRIGHT & LICENSE

Copyright 2009 John C. Norton.

This program is free software; you can redistribute it and/or modify it
under the terms of either: the GNU General Public License as published
by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.

=cut

###############
## Libraries ##
###############
use strict;
use warnings;
use Carp;
use Tk;


#############
## Globals ##
#############
my $b_drawing = 0;		# Disallow multiple simultaneous invocations

my $h_defaults = {
	'mouse'   => 1,
	'color'   => 'black',
	'fill'    => 0,
	'width'   => 1,
	'action'  => 0,
	'style'   => 'free',
};

my $h_aliases = {
	'a' => 'action',
	'c' => 'color',
	'f' => 'fill',
	'm' => 'mouse',
	'w' => 'width',
	's' => 'style',
};

my $h_styles = {
	'none'      => 'Do not draw anything, just collect points',
	'free'      => 'Join all points to create freehand lines (default)',
	'line'      => 'Join first/last points to create straight lines',
	'oval'      => 'Join first/last points to create ovals',
	'circle'    => 'Join first/last points to create circles',
	'rectangle' => 'Join first/last points to create rectangles',
};


###############
## Libraries ##
###############
sub new {
	my ($proto, $canvas, $c_result, $h_args) = @_;

	my $self = { 'points' => [ ], 'ids' => [ ], 'bindings' => { } };
	bless $self, $proto;

	$self->assign_args($h_args);

	($canvas   || 0) or $self->fatal("Missing Canvas argument (arg \$1)");
	($c_result || 0) or $self->fatal("Missing result callback (arg \$2)");

	$self->{'canvas'} = $canvas;
	$self->{'result'} = $c_result;

	my $mouse  = $self->{'mouse'};
	my $event  = $self->{'start_event'};
	my $a_draw = [ sub { $self->start_drawing(@_) }, Ev('x'), Ev('y') ];
	$self->new_binding($canvas, $event, $a_draw);

	return $self;
}


###############
## Accessors ##
###############
sub canvas { my ($self) = @_; $self->{'canvas'} }
sub mouse  { my ($self) = @_; $self->{'mouse'}  }
sub color  { my ($self) = @_; $self->{'color'}  }
sub fill   { my ($self) = @_; $self->{'fill'}   }
sub width  { my ($self) = @_; $self->{'width'}  }
sub style  { my ($self) = @_; $self->{'style'}  }


##########################
## User-visible Methods ##
##########################
sub restart {
	my ($self, $h_args) = @_;
	$self->assign_args($h_args);
	my $canvas = $self->{'canvas'};
	my $event  = $self->{'start_event'};
	my $a_draw = [ sub { $self->start_drawing(@_) }, Ev('x'), Ev('y') ];
	$self->new_binding($canvas, $event, $a_draw);
}


sub transform {
	my ($self, $a_points, $xoff, $yoff, $canvas) = @_;
	my $a_ids = [ ];
	my ($x0, $y0);

	$canvas  ||= $self->canvas;
	my $color  = $self->color;
	my $fill   = $self->fill;
	my $width  = $self->width;
	my $style  = $self->style;

	for (my $i = 0; $i < @$a_points; $i++) {
		my $a_point   = $a_points->[$i];
		my ($x1, $y1) = ( $a_point->[0] + $xoff, $a_point->[1] + $yoff );

		if ($i > 0) {
			my @args = ($x0, $y0, $x1, $y1);
			if ($style eq 'free' or $style eq 'line') {
				push @args, -width => $width;
				$color and push @args, -fill => $color;
				push @$a_ids, $canvas->createLine(@args);
			} elsif ($style eq 'oval') {
				push @args, -width => $width, -outline => $color;
				$fill and push @args, -fill => $fill;
				push @$a_ids, $canvas->createOval(@args);
			} elsif ($style eq 'rectangle') {
				push @args, -width => $width, -outline => $color;
				$fill and push @args, -fill => $fill;
				push @$a_ids, $canvas->createRectangle(@args);
			} elsif ($style eq 'circle') {
				my $rad  = sqrt(($x1 - $x0) ** 2 + ($y1 - $y0) ** 2);
				@args = ($x0 - $rad, $y0 - $rad, $x0 + $rad, $y0 + $rad);
				push @args, -width => $width, -outline => $color;
				$fill and push @args, -fill => $fill;
				push @$a_ids, $canvas->createOval(@args);
			}
		}

		($x0, $y0) = ($x1, $y1);
	}

	return $a_ids;
}


######################
## Internal Methods ##
######################
sub fatal {
	my ($self, $errmsg) = @_;
	carp "$errmsg\n";
	exit;
}


sub new_binding {
	my ($self, $canvas, $binding, $a_args) = @_;
	my $c_prev = $canvas->Tk::bind($binding);
	$self->{'bindings'}->{$binding} = $c_prev;
	$canvas->Tk::bind($binding => $a_args);
}


sub restore_bindings {
	my ($self, $canvas, $binding) = @_;
	my $c_prev = delete $self->{'bindings'}->{$binding};
	$canvas->Tk::bind($binding => $c_prev);
}


sub styles {
	print "[Available Tk::Draw styles]\n";
	foreach my $key (sort keys %$h_styles) {
		my $desc = $h_styles->{$key};
		printf "%10.10s .... %s\n", $key, $desc;
	}
}


sub assign_args {
	my ($self, $h_args) = @_;

	# Make a copy of user-supplied args, resolving aliases
	$h_args ||= { };
	my $h_copy = { };
	foreach my $k (keys %$h_args) {
		my $key = $h_aliases->{$k} || $k;
		$h_copy->{$key} = $h_args->{$k};
	}

	# Resolve all arguments
	foreach my $key (keys %$h_defaults) {
		my $val = delete $h_copy->{$key};
		if (defined($val)) {
			$self->{$key} = $val;
		} elsif (!defined($self->{$key})) {
			$self->{$key} = $h_defaults->{$key};
		}
	}

	# Give an error if any arguments were invalid
	my @leftover = keys %$h_copy;
	if (@leftover > 0) {
		my $s = (1 == @leftover)? "": "s";
		my $errstr = "Unknown Tk::Draw arg$s:  ";
		for (my $i = 0; $i < @leftover; $i++) {
			my $arg = $leftover[$i];
			$errstr .= ($i > 0)? ", '$arg'": "'$arg'";
		}
		$self->fatal($errstr);
	}

	# Determine action when mouse button is clicked/moving/released
	my $style = $self->{'style'};
	if (!exists($h_styles->{$style})) {
		my $styles = join(', ', keys %$h_styles);
		$self->fatal("Unknown style '$style' (must be one of {$styles})");
	}

	# Validate the mouse button
	my $mouse = $self->{'mouse'};
	if ($mouse !~ /^[123]$/) {
		$self->fatal("Unknown mouse '$mouse' (must be one of {1, 2, 3})");
	}

	# Assign events
	$self->{'start_event'} = "<Button-$mouse>";
	$self->{'stop_event'}  = "<ButtonRelease-$mouse>";
}


sub start_drawing {
	my ($self, $canvas, $x, $y) = @_;

	$b_drawing++ and return;

	push @{$self->{'points'}}, [ $self->{'x'} = $x, $self->{'y'} = $y ];

	my $a_move = [ sub { $self->keep_drawing(@_) }, Ev('x'), Ev('y') ];
	$self->new_binding($canvas, '<Motion>', $a_move);

	my $a_stop = [ sub { $self->stop_drawing(@_) }, Ev('x'), Ev('y') ];
	$self->new_binding($canvas, $self->{'stop_event'}, $a_stop);

	my $c_action = $self->{'action'};
	($c_action || 0) and $c_action->([ $x, $y ]);
}


sub keep_drawing {
	my ($self, $canvas, $x1, $y1) = @_;

	my ($x0, $y0) = ($self->{'x'}, $self->{'y'});

	my $style = $self->{'style'};
	if ($style ne 'none') {
		my $method = "style_$style";
		$self->$method($canvas, [ $x0, $y0, $x1, $y1 ]);
	}

	my $c_action = $self->{'action'};
	($c_action || 0) and $c_action->([ $x1, $y1 ]);
}


sub stop_drawing {
	my ($self, $canvas, $x, $y) = @_;

	my $h_bindings = $self->{'bindings'};
	foreach my $binding (keys %$h_bindings) {
		$self->restore_bindings($canvas, $binding);
	}

	my $c_result = $self->{'result'};
	my $a_points = $self->{'points'};
	my $a_ids    = $self->{'ids'};

	$self->{'points'} = [ ];
	$self->{'ids'}    = [ ];

	if (ref $c_result eq 'CODE') {
		$c_result->($self, $a_points, $a_ids, $canvas);
	}
	$b_drawing = 0;
}


#==========#
## Styles ##
#==========#
sub style_free {
	my ($self, $canvas, $a_points) = @_;

	my ($x0, $y0, $x1, $y1) = @$a_points;

	my $width = $self->{'width'};
	my $color = $self->{'color'};
	my $a_ids = $self->{'ids'};

	my @args = ( -width => $width, -fill => $color );
	push @$a_ids, $canvas->createLine($x0, $y0, $x1, $y1, @args);
	push @{$self->{'points'}}, [ $self->{'x'} = $x1, $self->{'y'} = $y1 ];
}


sub style_line {
	my ($self, $canvas, $a_points) = @_;

	my ($x1, $y1) = ($a_points->[-2], $a_points->[-1]);
	my ($x0, $y0) = @{$self->{'points'}->[0]};

	my $width = $self->{'width'};
	my $color = $self->{'color'};
	my $a_ids = $self->{'ids'};

	if (@$a_ids > 0) {
		pop @{$self->{'points'}};
		my $id = pop @{$self->{'ids'}};
		$canvas->delete($id);
	}

	my @args = ( -width => $width, -fill => $color );
	push @$a_ids, $canvas->createLine($x0, $y0, $x1, $y1, @args);
	push @{$self->{'points'}}, [ $self->{'x'} = $x1, $self->{'y'} = $y1 ];
}


sub style_oval {
	my ($self, $canvas, $a_points) = @_;

	my ($x1, $y1) = ($a_points->[-2], $a_points->[-1]);
	my ($x0, $y0) = @{$self->{'points'}->[0]};

	my $width = $self->{'width'};
	my $color = $self->{'color'};
	my $fill  = $self->{'fill'};
	my $a_ids = $self->{'ids'};

	if (@$a_ids > 0) {
		pop @{$self->{'points'}};
		my $id = pop @{$self->{'ids'}};
		$canvas->delete($id);
	}

	my @args = ( -width => $width, -outline => $color );
	$fill and push @args, -fill => $fill;
	push @$a_ids, $canvas->createOval($x0, $y0, $x1, $y1, @args);
	push @{$self->{'points'}}, [ $self->{'x'} = $x1, $self->{'y'} = $y1 ];
}


sub style_rectangle {
	my ($self, $canvas, $a_points) = @_;

	my ($x1, $y1) = ($a_points->[-2], $a_points->[-1]);
	my ($x0, $y0) = @{$self->{'points'}->[0]};

	my $width = $self->{'width'};
	my $color = $self->{'color'};
	my $fill  = $self->{'fill'};
	my $a_ids = $self->{'ids'};

	if (@$a_ids > 0) {
		pop @{$self->{'points'}};
		my $id = pop @{$self->{'ids'}};
		$canvas->delete($id);
	}

	my @args = ( -width => $width, -outline => $color );
	$fill and push @args, -fill => $fill;
	push @$a_ids, $canvas->createRectangle($x0, $y0, $x1, $y1, @args);
	push @{$self->{'points'}}, [ $self->{'x'} = $x1, $self->{'y'} = $y1 ];
}


sub style_circle {
	my ($self, $canvas, $a_points) = @_;

	my ($x1, $y1) = ($a_points->[-2], $a_points->[-1]);
	my $a_center  = $self->{'points'}->[0];
	my ($x0, $y0) = @$a_center;
	my $rad       = sqrt(($x1 - $x0) ** 2 + ($y1 - $y0) ** 2);

	# Create the box surrounding the larger circle
	my $a_corner1 = [ $x0 - $rad, $y0 - $rad ];
	my $a_corner2 = [ $x0 + $rad, $y0 + $rad ];

	my $width = $self->{'width'};
	my $color = $self->{'color'};
	my $fill  = $self->{'fill'};
	my $a_ids = $self->{'ids'};

	if (@$a_ids > 0) {
		pop @{$self->{'points'}};
		my $id = pop @{$self->{'ids'}};
		$canvas->delete($id);
	}

	my @args = ( -width => $width, -outline => $color );
	$fill and push @args, -fill => $fill;
	push @$a_ids, $canvas->createOval(@$a_corner1, @$a_corner2, @args);
	push @{$self->{'points'}}, [ $self->{'x'} = $x1, $self->{'y'} = $y1 ];
}


1;