Good day monks. I have a script with two subroutines that use GD and GD::Graph::lines to create graphics and write them to separate files. I am trying to refactor the code so the subroutines will return the GD objects instead, so I can comdine them into one graphic with GD's copy method and write a single file. However, I'm doing something wrong when it comes to passing the GD image object for the graph. Here is some simplified code that reproduces the problem
#!/usr/bin/perl -w
use strict;
use GD;
use GD::Graph::lines;

my $g = new GD::Image(400,300);
plot($g);
my $a = new GD::Image(20,300);
addon($a);
my $combined = new GD::Image(420,300);
$combined->copy($g,0,0,0,0,400,300);
$combined->copy($a,400,0,0,0,20,300);
open(OUT,">combined.png") or die "Can't open output: $!\n";
binmode OUT;
print OUT $combined->png;
close OUT;

sub plot {
    my ($graphimage) = @_;
    my @data = ( 
      ["1st","2nd","3rd","4th","5th","6th","7th", "8th", "9th"],
      [    1,    2,    5,    6,    3,  1.5,    1,     3,     4]
    );
    my $graph = GD::Graph::lines->new(400, 300);
    $graph->set( 
       x_label           => 'X Label',
       y_label           => 'Y label',
       title             => 'Some simple graph',
       y_max_value       => 8,
       y_tick_number     => 8,
       y_label_skip      => 2 
    ) or die $graph->error;
    $graphimage = $graph->plot(\@data) or die $graph->error;
    open(OUT,">combined-plotpart.png") or die "Can't open output: $!\n
+";
    binmode OUT;
    print OUT $graphimage->png;
    close OUT;
    return;
}

sub addon {
    my ($gdadd) = @_;
    my $blue = $gdadd->colorAllocate(0,0,255);
    $gdadd->rectangle(0,0,20,300,$blue);
    return;
}

[download]
When this is run, combined.png just has a big black square where the plot should be.

I'm baffled by this because when I write out the graphic in the plot subroutine (combined-plotpart.png) it has the correct graph, and I am passing it through a reference to the object just like for the addon image, which is working OK.

What am I doing wrong?

TIA....Steve

In reply to Problem passing GD image object by cormanaz

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