<?php

    $passes = 3;
    
    foreach(range(1, $passes) as $pass)
    {
        $range = $pass-1;
        printf("pass %d:", $pass);
        foreach(range(0, $range) as $y)
            foreach(range(0, $range) as $x)
                scan($x, $y);
        echo "\n\n";
    }


// this is just a mock, replace with your data
function scan($x, $y)
{
   static $yo = -1;
   if ($yo != $y) echo "\n";
   printf("{x%d,y%d} ", $x, $y);
   $yo = $y;
}

pass 1:
{x0,y0} 

pass 2:{x0,y0} {x1,y0} 
{x0,y1} {x1,y1} 

pass 3:
{x0,y0} {x1,y0} {x2,y0} 
{x0,y1} {x1,y1} {x2,y1} 
{x0,y2} {x1,y2} {x2,y2}