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Set B<-vertical_spacing> to 0 to completely suppress the diagonal
lines that connect the physical span of the feature to the image.

=head2 Specifying the Image

The path to the image can be specified in two ways. First, you can
place it in the feature itself using a tag named "image". Second, you
can specify it as a track option using a callback:

  $panel->add_track(\@features,
                    -glyph=>'image',
                    -image => sub { my $feature = shift;
                                    my $image_path = do_something();
                                    return $image }
                    );

You can of course give -image a constant string, in which case each
feature will show the same image.

The image can be a file on the local operating system or a
URL. However, URL fetching will only work if the LWP module is
installed on your system. Otherwise the glyph will fail with an error
message.

If the image is a relative path (it does not begin with a slash or a
URL protocol), then the contents of -image_prefix will be prepended to
it. This allows you to specify images that are relative to a
particular directory or a partial URL. Example:

  $panel->add_track(\@features,
                    -glyph => 'image',
                    -image_prefix => 'http://www.flybase.org/anatomy/image-browser_files',
                   );

This specifies that each feature's "image" tag is to be appended to
the partial FlyBase URL, thereby saving space.

=head2 Glyph Delegation

The image glyph consists of two parts: an upper part that shows the
extent of the feature in base pair coordinates, and a lower part that
shows the image. No scaling of the image is done; its height and width
are fixed.

By default the upper part uses the "generic" glyph, which is a simple
rectangle filled with the bgcolor and outlined with the fgcolor. To
use a different glyph in the upper part, specify the -glyph_delegate
option, giving the name of the glyph you wish to use. For instance, to
use the "span" glyph:

  $panel->add_track(\@features,
                    -glyph          => 'image',
                    -glyph_delegate => 'span'
                   );

This feature does not work with all glyphs, and in particular requires
a recent CVS checkout of Bio::Perl to work properly with the "arrow",
"span" and "primers" glyphs (support for the feature did not make it
into version 1.5).

=head1 BUGS AND LIMITATIONS

This glyph does not work with GD::SVG. If you try to render it onto a
GD::SVG panel, the image will be shown as a gray box. This will be
fixed in a future version of GD::SVG.

=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>, Todd Harris E<lt>harris@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