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##
## wml::des::preload - Preload Page Contents
## Copyright (c) 1997-2001 Ralf S. Engelschall, All Rights Reserved.
## Copyright (c) 2000-2001 Denis Barbier
##
# The <preserve>/<restore> tags with multiple arguments require WML 2.0.3
#use wml::mod::version
<require 2.0.3 />
#use wml::std::tags
<set-var __pl:count=0 />
<define-tag preload whitespace=delete>
<preserve src via />
<set-var via=size />
<set-var %attributes />
<increment __pl:count />
<when <string-eq "<get-var via />" "size" />>
<img name=preload_img_<get-var __pl:count />
src="<get-var src />"
width=1 height=1 alt="" />
</when>
<when <string-eq "<get-var via />" "js" />>
<copy-var src __pl:src />
# the <group> tag prevents deletion of newlines
<group "
<javascript>
if (document.images) {
preload_img_<get-var __pl:count /> = new Image();
preload_img_<get-var __pl:count />.src = '<get-var __pl:src />';
}
</javascript>
" />
</when>
<restore src via />
</define-tag>
##EOF##
__END__
=head1 NAME
wml::des::preload - Preload Images
=head1 SYNOPSIS
#use wml::des::preload
<preload src=<image filename> via=<trick>>
=head1 DESCRIPTION
This include file provides the C<E<lt>preloadE<gt>> tag which can be used to
preload images. Such preloading is usually done to speedup access for following
pages. Currently there are only a few tricks how this can be done.
The following combinations are currently supported:
=over 4
=item C<src=>I<anyimage> C<via=size>
Preloads the image I<anyimage> by using an C<E<lt>imgE<gt>> tag with the
attributes C<width=1 height=1> which leads to the loading of the image but
only to a 1 pixel in display.
Advantage: Works for all browsers.
Disadvantage: This approach has the nasty side-effect of an occuring 1 pixel
in display because C<width=0 height=0> does not work as expected in most
browsers (especially in Netscape 4.x). So, position your C<E<lt>preloadE<gt>>
tag somewhere it does not destroy the look and feel of your page.
=item C<src=>I<anyimage> C<via=js>
Preloads the image I<anyimage> by using a JavaScript snippet which loads
the image by declaring an unused C<Image> object.
Advantage: Silently preloads the image without displaying anything.
Disadvantage: Only works for browsers with a JavaScript implementation and
only for those who support the C<Image> object (currently NS/3, NS/4, IE/4).
=back
=head1 AUTHORS
Ralf S. Engelschall
rse@engelschall.com
www.engelschall.com
Denis Barbier
barbier@engelschall.com
=head1 REQUIRES
Internal: P1, P2
External: --
=head1 SEE ALSO
wml::std::tags(3)
HTML 3.2 C<E<lt>imgE<gt>> tag.
=cut
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