Question

I have the following code:

use Imager::Screenshot 'screenshot';
my $img = screenshot(hwnd => 'active', 
    left => 450, 
    right => 200, 
    top => 50, 
    bottom => 50
);
$img->write(file => 'screenshot.png', type => 'png' ) || 
    print "Failed: ", $img->{ERRSTR} , "\n";

it prints:

“Can’t call method “write” on undefined value at line 3″

but when I do:

use Imager::Screenshot 'screenshot';
my $img = screenshot(hwnd => 'active', 
    left => 100, 
     right => 300, 
     top => 100, 
     bottom => 300
);

$img->write(file => 'screenshot.png', type => 'png' ) || 
     print "Failed: ", $img->{ERRSTR} , "\n";

It does take a screenshot. Why would the left, right, top and bottom values matter here?

EDIT:
After some research I found out that left param must be smaller than right param and top must be smaller than bottom.

Answer 1

Have you tried checking the error? e.g.

my $img = screenshot(...) or die Imager->errstr;

edit: try this code:

use Imager::Screenshot 'screenshot';
my $img = screenshot(hwnd => 'active',
    left => 450, 
    right => 200, 
    top => 50, 
    bottom => 50
) or die Imager->errstr;
$img->write(file => 'screenshot.png', type => 'png' ) || 
    print "Failed: ", $img->errstr, "\n";