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Subject Author Date
Mixing HTML::Template and GD::Graph Colin Walls 05-14-2005
Posted by Colin Walls on May 14, 2005, 8:53 am
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I have developed an application using CGI::Application and HTML::Template.
Some of the run modes in the application use GD:Graph to present charts.

In the GD:Graph documentation they simply write graphical information to
STDOUT to present the information to a web page. I can't work out whether
this is possible using HTML::Template, and if it is, how to do it. As a
result I am writing the charts to a file and using a standard image tag in
my template file.

Is it possible to write present a GD:Graph chart without writing a file in
this scenario?

--
Colin Walls
Removed the pink meat to mail me


Posted by Sherm Pendley on May 14, 2005, 4:58 am
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Colin Walls wrote:
> I have developed an application using CGI::Application and HTML::Template.
> Some of the run modes in the application use GD:Graph to present charts.
>
> In the GD:Graph documentation they simply write graphical information to
> STDOUT to present the information to a web page. I can't work out whether
> this is possible using HTML::Template, and if it is, how to do it. As a
> result I am writing the charts to a file and using a standard image tag in
> my template file.
>
> Is it possible to write present a GD:Graph chart without writing a file in
> this scenario?

Yes, but probably not in the way you're thinking. There's no getting
around the fact that the user agent will be making a second, entirely
separate request for the image data. So you can't print the image and
HTML as part of the same request.

What you can do is, within the HTML::Template CGI, construct an img
element whose src attribute points to a second CGI that prints the
image, and includes in the query string any parameters that one will
need to do its job.

sherm--

--
Cocoa programming in Perl: http://camelbones.sourceforge.net
Hire me! My resume: http://www.dot-app.org


Posted by Ignoramus4744 on May 14, 2005, 1:41 pm
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As someone else said, the browser makes a separate request for files
anyway.

I use GD::Graph on my site a lot. I use it for drawing cute math
formulas.

For example, I could plot a formula x[1,2] = (-b+-sqrt( b^2-4ac ) )/2a
and it would be painted, you can play with it at

http://www.algebra.com/services/rendering/

It is done without writing to files. Note declaration my $jpeg and
print $jpeg. (as a complication, these jpegs are saved into my binary
cache MySQL table for future reuse).

sub main() {
my $jpeg;

print $cgi->header(-type=>'image/jpeg', -expires=>'+1d');

# try to look up the binary cache right away!
my $formula_id = "formula: $expr";

my $use_cache = 1;

if( $use_cache ) {
$jpeg = retrieve_item_from_binary_cache( $formula_id );

if( defined $jpeg ) {
print $jpeg;
return;
}
}
$full_expr = $expr;
#print STDERR "$0: Rendering '$expr'.\n";
my $parsed = create_parsed_expression( $expr );

my $im;
if ( !$global_error ) {
calculate_sizes( $parsed );
$im = paint( $parsed );
} else { # error
$im = paint_error_message( $global_error );
}

if ( $cgi->param( "cross" ) ) {
$im->line( 0, 0, $parsed->, $parsed->, $red );
$im->line( 0, $parsed->, $parsed->, 0, $red );
}
$jpeg = $im->jpeg( 70 );
print $jpeg;

store_item_in_binary_cache( $formula_id, "formula", $jpeg );



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