Filled polygone is not rendered 129th time on same image

I have a function which creates a polygon of blue color. I call this function inside a loop of 128 iterations. For every iteration, i change the value of x and y so that my polygon is rendered on new location. This goes fine and i get 128 new polygons on my image after running the script. But if change the number to 129, the 129th polygon is transparent or what i cannot guess. It just does not display or render at all. Is this a bug or some mistake with my code?

I am using php version 5.1.4 that came with WAMP5 Version 1.6.3

my code is -
<?php
$im = imagecreate(600, 400);
$x = 20;
$y = 350;
for($i=1;$i<=128;$i++) //create a polygon 128 times
{
drawPoly($x,$y,$im);
$x = $x+2;
$y = $y-2;
}
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);
function drawPoly($xCoord,$yCoord,$im)
{
$x1 = $x2 = $xCoord;
$x3 = $x4 = $xCoord + 70;
$y1 = $y4 = $yCoord;
$y2 = $y3 = $yCoord + 30;
$Poly = array(0 => $x1,1 => $y1,2 => $x2,3 => $y2,4 => $x3,5 => $y3,6

=> $x4,7 => $y4);
$bg = imagecolorallocate($im, 150, 150, 150);
$blue = imagecolorallocate($im, 0, 0, 255);
imagefilledpolygon($im, $Poly, 4, $blue);
}
?>

 

The issue is solved. It was the problem with the code.

i took this line $bg = imagecolorallocate($im, 150, 150, 150); outside the function drawPoly(), and everything worked as

expected.

the new updated code is -

<?php
$im = imagecreate(600, 400);
$bg = imagecolorallocate($im, 150, 150, 150);
$x = 20;
$y = 350;
for($i=1;$i<=150;$i++) //create a polygon 128 times
{
drawPoly($x,$y,$im);
$x = $x+2;
$y = $y-2;
}
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);
function drawPoly($xCoord,$yCoord,$im)
{
$x1 = $x2 = $xCoord;
$x3 = $x4 = $xCoord + 70;
$y1 = $y4 = $yCoord;
$y2 = $y3 = $yCoord + 30;
$Poly = array(0 => $x1,1 => $y1,2 => $x2,3 => $y2,4 => $x3,5 => $y3,6 => $x4,7 => $y4);
$blue = imagecolorallocate($im, 0, 0, 255);
imagefilledpolygon($im, $Poly, 4, $blue);
}
?>

But i still want to know why this happened and why it worked when i took that line outside the function?