sub event_handler {
    my ( $widget, $event ) = @_;
    # print $widget ,' ',$event->type,"\n";
    
    #on 2 mouse presses, place waypoint 
    if ( $event->type eq "2button-press" ) {
        print 'x->',$event->x,'  ','y->',$event->y;
        
        #convert UTM to Lat and Long
        my $easting = $ps[0] * $event->x + 0.0 * $event->y + $mtp[3];
        my $northing = (-$ps[1]) * $event->y + 0.0 * $event->x + $mtp[
+4];
        my ($latitude,$longitude)=utm_to_latlon($ellipsoid,$zone,$east
+ing,$northing);
        print " ($latitude, $longitude)\n";
        
        #Drop icon
        my $tgroup = Gnome2::Canvas::Item->new ($root, 'Gnome2::Canvas
+::Group', x => $event->x, y => $event->y);
        Gnome2::Canvas::Item->new($tgroup, 'Gnome2::Canvas::Ellipse',
            x1 => -7.5,
            y1 => -7.5,
            x2 => 7.5,
            y2 => 7.5,
            fill_color => 'purple',
            outline_color => 'black');
        Gnome2::Canvas::Item->new ($tgroup,
            'Gnome2::Canvas::Text',
            "text", "$count",
            "x", 0.0,
            "y", 0.0,
            "font", "Sans Bold",
            "anchor", 'GTK_ANCHOR_NW',
            "weight", 100,
            "fill_color", 'red',
            "size_points", 20);
        
        
        #add waypoints
        $waypoints{$count } = {'x' => $event->x,'y' => $event->y, 'lat
+' => $latitude, 'long' => $longitude};
        print "size of hash:  " . keys( %waypoints ) . ".\n";
        #foreach my $num (sort keys %waypoints){
        #    print "$num = $waypoints{$num}\n";
        #    foreach my $subkey (sort keys %{$waypoints{$num}}){
        #        print "$subkey = $waypoints{$num}{$subkey}\n";
        #    }
        #}

        
        #draw lines to the waypoints
        if ($count >= 2){
            my @points;
            foreach my $key (sort keys %waypoints){
                foreach my $subkey (sort keys %{$waypoints{$key}}){
                    if ($subkey eq 'x' || $subkey eq 'y'){
                        push(@points, $waypoints{$key}{$subkey});
                        print "$key $subkey = $waypoints{$key}{$subkey
+}\n";
                    }
                    
                }
                
            }
            if ($count >= 3){
                push(@points, $waypoints{1}{'x'});
                push(@points, $waypoints{1}{'y'});
            }
            
            my $lgroup = Gnome2::Canvas::Item->new ($root, 'Gnome2::Ca
+nvas::Group');
            Gnome2::Canvas::Item->new ($lgroup,
                'Gnome2::Canvas::Line',
                points => [@points],
                fill_color => 'black',
                width_units => 4.0);
            
            foreach (@points){
                print $_, "\n";
            }   
        }
        #print $count, "\n";
        $tgroup->raise_to_top();
        $count++;
    }
}
[download]

UPDATE 6/3/2008 ..... I found the mouse position error, It was caused by the scrollregion being made smaller than the default canvas size!! See fixed code below.

I'm not sure on the best way to filter out the extra line segment, it seems like a college level math problem, but the first thing that comes to mind is to just make a single line with multiple points. That way you just push the new waypoint onto the points for the line. Each waypath is just a single line with multiple points. This is just a simple example, but should show the idea. Like you, I can't get the mouse coordinates to line up. I'm totally confused on it and will ask on the maillist. It has something to do with groups and centering.

#!/usr/bin/perl
use warnings;
use strict;
use Gtk2 -init;
use Gnome2::Canvas;

my $window   = Gtk2::Window->new;
$window->signal_connect( destroy => sub { exit } );

my $scroller = Gtk2::ScrolledWindow->new;
my $canvas   = Gnome2::Canvas->new();
$scroller->add( $canvas );
$window->add( $scroller );
$window->set_default_size( 500, 500 );


# if scrollregion is smaller than default_size, a weird
# coordinate transform occurs
# $canvas->set_scroll_region( 0, 0, 400, 400 ); # bad
$canvas->set_scroll_region( 0, 0, 700, 700 ); # works good

$window->show_all;

my $root = $canvas->root;

# a stupid hack to try and compensate for bad scrollregion ;-(
#$root->move(-50,-50);  # dumb

my $text = Gnome2::Canvas::Item->new(
    $root, 'Gnome2::Canvas::Text',
   x          => 20,
   y          => 15,
   fill_color => 'black',
   font       => 'Sans 14',
   anchor     => 'GTK_ANCHOR_NW',
   text       => 'Click to add waypoint'
);

$canvas->signal_connect (event => \&event_handler);

my $points = [0,0,100,100];

my $line2= Gnome2::Canvas::Item->new ($root,
        'Gnome2::Canvas::Line',
         points => $points,
        fill_color => "red",
        width_units => 3.0,
        cap_style => 'projecting',
         join_style => 'miter',
        );

my $p = $line2->get('points');
print "@$p\n";
my ($x,$y) = @$p;

Gtk2->main;

##############################

sub event_handler{
     my ( $widget, $event ) = @_;
#     print $widget ,' ',$event->type,"\n";

    if ( $event->type eq "button-press" ) {
        print 'x->',$event->x,'  ','y->',$event->y,"\n";

        push @$points,$event->x , $event->y;

        $line2->set(points=>$points);

        my $p = $line2->get('points');
        print "@$p\n";
  
    }    
}

__END__
[download]

---

I'm not really a human, but I play one on earth CandyGram for Mongo

UPDATE.... see fix above.....it just goes to show how one stupid sizing error can lead to multiple corrective hacks :-)

It has something to do with groups and centering.

It seems to be more than that, it also has something to do with the scrollregion. If I adjust the scrollregion, it seems to work, but as to why? I'm still experimenting. :-) Moving the canvas -50 -50 still is a complete mystery. It must be something so obvious, that I'm completely missing it.

$canvas->set_scroll_region( -20, -20, 400, 400 );
[download]

---

I'm not really a human, but I play one on earth CandyGram for Mongo