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               the automatic "track" and "group"
               glyphs.

  -grid        Whether to draw a vertical grid in    false
               the background.  Pass a scalar true
               value to have a grid drawn at
               regular intervals (corresponding
               to the minor ticks of the arrow
	       glyph).  Pass an array reference
               to draw the grid at the specified
               positions.

  -gridcolor   Color of the grid                     lightcyan

  -gridmajorcolor Color of grid major intervals      cyan

  -extend_grid If true, extend the grid into the pad false
               top and pad_bottom regions

  -background  An image or callback to use for the   none
               background of the image. Will be
               invoked I<before> drawing the grid.

  -postgrid    An image or callback to use for the   none
               background of the image.  Will be 
               invoked I<after> drawing the grid.

  -truecolor   Create a truecolor (24-bit) image.    false
               Useful when working with the
               "image" glyph.

  -truetype    Render text using scaleable vector    false
               fonts rather than bitmap fonts.

  -image_class To create output in scalable vector
               graphics (SVG), optionally pass the image
               class parameter 'GD::SVG'. Defaults to
               using vanilla GD. See the corresponding
               image_class() method below for details.

  -link, -title, -target
               These options are used when creating imagemaps
               for display on the web.  See L</"Creating Imagemaps">.


Typically you will pass new() an object that implements the
Bio::RangeI interface, providing a length() method, from which the
panel will derive its scale.

  $panel = Bio::Graphics::Panel->new(-segment => $sequence,
				     -width   => 800);

new() will return undef in case of an error.

Note that if you use the "left" or "right" key styles, you are
responsible for allocating sufficient -pad_left or -pad_right room for
the labels to appear.  The necessary width is the number of characters
in the longest key times the font width (gdMediumBoldFont by default)
plus 3 pixels of internal padding.  The simplest way to calculate this
is to iterate over the possible track labels, find the largest one,
and then to compute its width using the formula:

  $width = gdMediumBoldFont->width * length($longest_key) +3;

In order to obtain scalable vector graphics (SVG) output, you should
pass new() the -image_class=E<gt>'GD::SVG' parameter. This will cause
Bio::Graphics::Panel to load the optional GD::SVG module. See the gd()
and svg() methods below for additional information.

You can tile an image onto the panel either before or after it draws
the grid. Simply provide the filename of the image in the -background
or -postgrid options. The image file must be of type PNG, JPEG, XBM or
GIF and have a filename ending in .png, .jpg, .jpeg, .xbm or .gif.

You can also pass a code ref for the -background or -postgrid option,
in which case the subroutine will be invoked at the appropriate time
with the GD::Image object and the Panel object as its two arguments.
You can then use the panel methods to map base pair coordinates into
pixel coordinates and do some custom drawing.  For example, this code
fragment will draw a gray rectangle between bases 500 and 600 to
indicate a "gap" in the sequence:

  my $panel = Bio::Graphics::Panel->new(-segment=>$segment,
                                        -grid=>1,
                                        -width=>600,
                                        -postgrid=> \&draw_gap);
  sub gap_it {
     my $gd    = shift;
     my $panel = shift;
     my ($gap_start,$gap_end) = $panel->location2pixel(500,600);
     my $top                  = $panel->top;
     my $bottom               = $panel->bottom;
     my $gray                 = $panel->translate_color('gray');
     $gd->filledRectangle($gap_start,$top,$gap_end,$bottom,$gray);
}

The B<-truetype> argument will activate rendering of labels using
antialiased vector fonts. If it is a value of "1", then labels will be
rendered using the default font (Verdana). Pass a font name to use
this font as the default:

  -truetype => 'Times New Roman',

Note that you can change the font on a track-by-track basis simply by
using a truetype font name as add_track()'s -font argument.

=back

=head2 OBJECT METHODS

=over 4

=item $track = $panel-E<gt>add_track($glyph,$features,@options)

The add_track() method adds a new track to the image. 

Tracks are horizontal bands which span the entire width of the panel.
Each track contains a number of graphical elements called "glyphs",
corresponding to a sequence feature. 

There are a large number of glyph types.  By default, each track will