my $self = shift;

  # bail out if this isn't the right kind of feature
  # handle both das-style and Bio::SeqFeatureI style,
  # which use different names for subparts.
  my @parts = $self->parts;
  @parts    = $self if !@parts && $self->level == 0;
  return $self->SUPER::draw(@_) unless @parts;

  # figure out the colors
  my $max_score = $self->option('max_score');
  my $min_score = $self->option('min_score');
  unless (defined $max_score && defined $min_score) {
    for my $part (@parts) {
      my $s = eval { $part->feature->score };
      next unless defined $s;
      $max_score = $s if !defined $max_score or $s > $max_score;
      $min_score = $s if !defined $min_score or $s < $min_score;
    }
  }

  return $self->SUPER::draw(@_)
    unless defined($max_score) && defined($min_score)
      && $min_score < $max_score;

  my $span = $max_score - $min_score;

  # allocate colors
  my $fill   = $self->bgcolor;
  my ($red,$green,$blue) = $self->panel->rgb($fill);

  foreach my $part (@parts) {
    my $s = eval { $part->feature->score };
    unless (defined $s) {
      $part->{partcolor} = $fill;
      next;
    }
    my ($r,$g,$b) = $self->calculate_color($s,[$red,$green,$blue],$min_score,$span);
    my $idx      = $self->panel->translate_color($r,$g,$b);
    $part->{partcolor} = $idx;
  }
  $self->SUPER::draw(@_);

  my $self = shift;
  my ($s,$rgb,$min_score,$span) = @_;
  return map { 255 - (255-$_) * min(max( ($s-$min_score)/$span, 0), 1) } @$rgb;
}

sub min { $_[0] < $_[1] ? $_[0] : $_[1] }
sub max { $_[0] > $_[1] ? $_[0] : $_[1] }

sub subseq {
  my $class = shift;
  my $feature = shift;
  return $feature->segments        if $feature->can('segments');
  return $feature->sub_SeqFeature  if $feature->can('sub_SeqFeature');
  return;
}

# synthesize a key glyph
sub keyglyph {
  my $self = shift;

  my $scale = 1/$self->scale;  # base pairs/pixel

  # two segments, at pixels 0->50, 60->80
  my $offset = $self->panel->offset;

  my $feature =
    Bio::Graphics::Feature->new(
				-segments=>[ [ 0*$scale +$offset,20*$scale+$offset],
					     [ 30*$scale +$offset,50*$scale+$offset],
					     [60*$scale+$offset, 80*$scale+$offset]
					   ],
				-name => $self->option('key'),
				-strand => '+1');
  ($feature->segments)[0]->score(10);
  ($feature->segments)[1]->score(50);
  ($feature->segments)[2]->score(100);
  my $factory = $self->factory->clone;
  $factory->set_option(label => 1);
  $factory->set_option(bump  => 0);
  $factory->set_option(connector  => 'solid');
  return $factory->make_glyph($feature);
}

# component draws a shaded box
sub bgcolor { 
  my $self = shift;
  return $self->{partcolor} || $self->SUPER::bgcolor;
}
sub fgcolor { 
  my $self = shift;
  return $self->{partcolor} || $self->SUPER::fgcolor;
}

1;

=head1 NAME

Bio::Graphics::Glyph::graded_segments - The "graded_segments" glyph

=head1 SYNOPSIS

  See L<Bio::Graphics::Panel> and L<Bio::Graphics::Glyph>.

=head1 DESCRIPTION

This is identical to the "alignment" glyph, and is used for
drawing features that consist of discontinuous segments.  The
color intensity of each segment is proportionate to the score.

=head2 OPTIONS

The following options are standard among all Glyphs.  See
L<Bio::Graphics::Glyph> for a full explanation.

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

  -fgcolor      Foreground color	       black

  -outlinecolor	Synonym for -fgcolor

  -bgcolor      Background color               turquoise

  -fillcolor    Synonym for -bgcolor

  -linewidth    Line width                     1

  -height       Height of glyph		       10

  -font         Glyph font		       gdSmallFont

  -connector    Connector type                 0 (false)

  -connector_color
                Connector color                black

  -label        Whether to draw a label	       0 (false)

  -description  Whether to draw a description  0 (false)

In addition, the alignment glyph recognizes the following
glyph-specific options:

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

  -max_score  Maximum value of the	   Calculated
              feature's "score" attribute

  -min_score  Minimum value of the         Calculated
              feature's "score" attribute

If max_score and min_score are not specified, then the glyph will
calculate the local maximum and minimum scores at run time.


=head1 BUGS

Please report them.

=head1 SEE ALSO

L<Bio::Graphics::Panel>,
L<Bio::Graphics::Glyph>,
L<Bio::Graphics::Glyph::arrow>,
L<Bio::Graphics::Glyph::cds>,
L<Bio::Graphics::Glyph::crossbox>,
L<Bio::Graphics::Glyph::diamond>,
L<Bio::Graphics::Glyph::dna>,
L<Bio::Graphics::Glyph::dot>,
L<Bio::Graphics::Glyph::ellipse>,
L<Bio::Graphics::Glyph::extending_arrow>,
L<Bio::Graphics::Glyph::generic>,
L<Bio::Graphics::Glyph::graded_segments>,
L<Bio::Graphics::Glyph::heterogeneous_segments>,
L<Bio::Graphics::Glyph::line>,
L<Bio::Graphics::Glyph::pinsertion>,
L<Bio::Graphics::Glyph::primers>,
L<Bio::Graphics::Glyph::rndrect>,
L<Bio::Graphics::Glyph::segments>,
L<Bio::Graphics::Glyph::ruler_arrow>,
L<Bio::Graphics::Glyph::toomany>,
L<Bio::Graphics::Glyph::transcript>,
L<Bio::Graphics::Glyph::transcript2>,
L<Bio::Graphics::Glyph::translation>,
L<Bio::Graphics::Glyph::triangle>,
L<Bio::DB::GFF>,
L<Bio::SeqI>,
L<Bio::SeqFeatureI>,
L<Bio::Das>,
L<GD>

=head1 AUTHOR

Lincoln Stein E<lt>lstein@cshl.orgE<gt>

Copyright (c) 2001 Cold Spring Harbor Laboratory

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.  See DISCLAIMER.txt for
disclaimers of warranty.

=cut