NAME

GD::Graph::Hooks - Kludgey way to add callback hooks to GD::Graph

SYNOPSIS

    use GD::Graph::Hooks;
    use GD::Graph::lines;

    my @data;
    for( 0 .. 100 ) { push @{$data[0]}, $_; push @{$data[1]}, $_ + 3*(rand 5); }

    # compute a naive biased moving average
    my (@mv_avg, @last);
    for my $i ( 0 .. $#{ $data[1] }) {
        push @last, $data[1][$i];
        if( @last > 4 ) {
            shift @last while @last > 5;
            my $sum = 0;
               $sum += $_ for @last;
            $mv_avg[$i] = ($sum / @last);
        }
    }

    my $graph = GD::Graph::lines->new(1500,500);

    $graph->add_hook( 'GD::Graph::Hooks::PRE_DATA' => sub {
        my ($gobj, $gd, $left, $right, $top, $bottom, $gdta_x_axis) = @_;
        my $clr = $gobj->set_clr(0xaa, 0xaa, 0xaa);

        my $x = 10;
        while ( $x < $#{ $data[1] }-10 ) {
            # compute line endpoints from a datapoint
            my @lhs = $gobj->val_to_pixel($x+1,  $data[1][$x]);

            # to a predicted endpoint, based on the moving average
            my @rhs = $gobj->val_to_pixel($x+11, $data[1][$x] + 10*($mv_avg[$x] - $mv_avg[$x-1]));

            print "adding line from data point (@lhs) to value predicted by mv_avg (@rhs)\n";

            $gd->line(@lhs,@rhs,$clr);

            $x += 10;
        }
    });

    my $gd = $graph->plot(\@data);

    my $fname = "/tmp/example.png";
    open my $img, '>', $fname or die $!;
    binmode $img;
    print $img $gd->png;
    close $img;

    print "example written to $fname\n";

Possible hook names follow. This documentation is sparse because you either got what you needed above already or you'll need to go source diving anyway. The hooks appear as pairs because they are just different names for the same event.

POST_INIT / PRE_TEXT
POST_TEXT / PRE_AXIS
POST_AXIS / PRE_DATA
POST_DATA / PRE_VALUES
POST_VALUES / PRE_LEGEND
POST_LEGEND / PRE_RETURN

AUTHOR

Paul Miller <jettero@cpan.org>

I am using this software in my own projects... If you find bugs, please please please let me know. I do use RT.

COPYRIGHT

Copyright © 2015 Paul Miller

LICENSE

This is released under the Artistic License. See perlartistic.

SEE ALSO

perl(1), GD::Graph