# main thread
my( $X, $Y ) = ...;

for my $y ( 0 .. $Y-1 ) {
    $Q->enqueue( [ $X, $y ] );     
}

## drawing thread
while( my( $x, $y ) = @{ $Q->dequeue } ) {
    $image->setpixel( $_, $y, ... ) for 0 .. $X-1;
}