primers documentation.

This glyph draws two arrows oriented towards each other and connected
by a line of a contrasting color. The length of the arrows is
immaterial, but the length of the glyph itself corresponds to the
length of the scaled feature. In addition to the common options, the following glyph-specific
options are recognized:

  Option      Description               Default
  ------      -----------               -------

  -connect    Whether to connect the      true
              two arrowheads by a line.

  -connect_color  The color to use for the    bgcolor
              connecting line.

sub draw {

  my $self = shift;
  my $gd = shift;
  my ($x1,$y1,$x2,$y2) = $self->calculate_boundaries(@_);

  my $fg = $self->fgcolor;
  my $a2 = HEIGHT/2;
  my $center = $y1 + $a2;

  # just draw us as a solid line -- very simple
  if ($x2-$x1 < HEIGHT*2) {
    $gd->line($x1,$center,$x2,$center,$fg);
    return;
  }

  # otherwise draw two pairs of arrows
  # -->   <--
  my $trunc_left  = $x1 < $self->panel->left;
  my $trunc_right = $x2 > $self->panel->right;

  unless ($trunc_left) { 
    $gd->line($x1,$center,$x1 + HEIGHT,$center,$fg);
    $gd->line($x1 + HEIGHT,$center,$x1 + HEIGHT - $a2,$center-$a2,$fg);
    $gd->line($x1 + HEIGHT,$center,$x1 + HEIGHT - $a2,$center+$a2,$fg);
  }

  unless ($trunc_right) {
    $gd->line($x2,$center,$x2 - HEIGHT,$center,$fg);
    $gd->line($x2 - HEIGHT,$center,$x2 - HEIGHT + $a2,$center+$a2,$fg);
    $gd->line($x2 - HEIGHT,$center,$x2 - HEIGHT + $a2,$center-$a2,$fg);
  }

  # connect the dots if requested
  if ($self->connect) {
    my $c = $self->color('connect_color') || $self->bgcolor;
    $gd->line($x1 + ($trunc_left  ? 0 : HEIGHT + 2),$center,
	      $x2 - ($trunc_right ? 0 : HEIGHT + 2),$center,
	      $c);
  }

  # add a label if requested
  $self->draw_label($gd,@_)       if $self->option('label');
  $self->draw_description($gd,@_) if $self->option('description');

}

connect	No description	Code
draw	No description	Code