Greetings vr,

Cool gradient background! I tried adding frames simultaneously while running by modifying the gather code block.

  gather      => sub {
    if (@_ == 1) {
      print "\r", $count++;
    }
    else {
      if (!defined $gifdata) {
        $image    = GD::Image-> newFromGifData( shift @{ $_[1] } );
        $gifdata  = $image-> gifanimbegin( 0,0 );
        $gifdata .= $image-> gifanimadd( 1,0,0,1,1 );
      }
      while ( my $data = shift @{ $_[1] } ) {
        my $frame = GD::Image-> newFromGifData( $data );
        $gifdata .= $frame-> gifanimadd( 1,0,0,1,1 );
      }
    }
  },
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That results in workers waiting for the manager process which is fine (i.e. the manager process is now the bottleneck). In that case chunk_size 1 may be faster to have the manager process quickly add one frame. Thereby able to respond to other workers with lesser latency.

use strict;
use warnings;
use feature 'say';
use Imager;
use MCE::Loop;
use Time::HiRes 'time';
use GD;

STDOUT->autoflush;

my $start = time;
my $count = 0;

my $bkg;
my $image;
my $gifdata;

MCE::Loop->init(
  max_workers => MCE::Util::get_ncpu(),
  chunk_size  => 1,
  init_relay  => '',

  gather      => sub {
    if (@_ == 1) {
      print "\r", $count++;
    }
    else {
      if (!defined $gifdata) {
        $image    = GD::Image-> newFromGifData( shift @{ $_[1] } );
        $gifdata  = $image-> gifanimbegin( 0,0 );
        $gifdata .= $image-> gifanimadd( 1,0,0,1,1 );
      }
      while ( my $data = shift @{ $_[1] } ) {
        my $frame = GD::Image-> newFromGifData( $data );
        $gifdata .= $frame-> gifanimadd( 1,0,0,1,1 );
      }
    }
  },

  user_begin => sub {
    $bkg = Imager->new(xsize=>800, ysize=>600);
    $bkg->filter(type=>"gradgen",
                 xo=>[ 100, 300, 600 ],
                 yo=>[ 100, 300, 100 ],
                 colors=>[ qw(red blue green) ]);
    $bkg->filter(type=>"noise", amount=>12, subtype=>0)
  },
);

mce_loop {
  my ($mce, $chunk_ref, $chunk_id) = @_;
  my @i_data;

  for my $x (@{ $chunk_ref }) {
    my $i = $bkg-> copy;

    $i->string(
      text  => $x,
      color => Imager::Color->new('ffffff'),
      font  => Imager::Font->new(
      # file  => '/usr/share/fonts/truetype/msttcorefonts/cour.ttf', #
+ Ubuntu
      # file  => '/System/Library/Fonts/Courier.dfont',
        face  => 'Courier New', # mswin
        size  => 420,
        aa    => 1),
      x     => 25,
      y     => 500,
    );

    $i->write(data => \my $data, type => 'gif');
    push @i_data, $data;

    MCE->gather($x);
  }

  MCE::relay { MCE->gather($chunk_id, \@i_data) };

} [ 0 .. 319 ];

MCE::Loop->finish;

print " frame GIF done!\n";
printf "compute time: %0.3fs\n", time - $start;

$gifdata .= $image-> gifanimend;

open my $fh, '>:raw', 'gd.gif';
print $fh $gifdata;
close $fh;

printf "Total: %0.3fs\n", time - $start;
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Regards, Mario