It looks like there are waves beetween the points, but it's straight.
<?php
$maxwert = 300;
$size = 10;
$img = imagecreatetruecolor($maxwert, $maxwert);
imagecolorallocate($img, 0, 0, 0);
for($y=0;$y<$maxwert;$y += $size){
for($x=0;$x<$maxwert;$x+=$size){
$r = rand(0,255);
$g = rand(0,255);
$b = rand(0,255);
$color = imagecolorallocate($img, $r, $g, $b);
imagefilledrectangle ($img, $x, $y, $x+$size ,$y+$size, $color);
}
}
header("Content-type: image/png");
imagepng($img);
?>