"I cannot make any connection between this post and the earlier 2 in the series"

Sorry BrowserUK for being imprecise, i'll try to give some more information:

Short time ago i wrote a script for learning purposes and fun that renders a huge image (20 MP) in ~13m on my box

I'd like to write a multithreaded version of this script.

The basic idea is to do it "row by row".

Enqueue some rows of the image and process them...

* * * * * * * * * * * * * * * * * * * * 
* * * * * * * * * * * * * * * * * * * *
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
[download]

...next step...

x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
* * * * * * * * * * * * * * * * * * * * 
* * * * * * * * * * * * * * * * * * * *
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x x x x
[download]

...proceed until finished.

The snippet in my OP calculates the coordinates for the rows.

For $width = 4; $height = 4; $qsize  = 4; the output is:

[
  [[0, 0], [0, 1], [0, 2], [0, 3]],
  [[1, 0], [1, 1], [1, 2], [1, 3]],
  [[2, 0], [2, 1], [2, 2], [2, 3]],
  [[3, 0], [3, 1], [3, 2], [3, 3]],
]
[download]

@queue should perhaps better been named @rows.

Then:

my $queue = Thread::Queue->new();
$queue->enqueue(\@rows);
my @threads = map { threads->create( \&process, $queue ); } 1 .. 4;
...
[download]

Somewhere in the code:

if ( $div == 0 ) {
    $image->setpixel( x => $x, y => $y, color => $black );
} 
else {
    $image->setpixel( x => $x, y => $y, color => $palette[$color] );
}
[download]

OK, busted. It's a Mandelbrot. My first try.

I hope very much that i could clarify the connection of my OP to the series.

Best regards, Karl