Menuknapper med gd2

hej

Jeg har lavet en menuknaps -php fil som har nogle underlige felter på sig:

<?php
   
    $img_w = (isset($_GET["w"]) && $_GET["w"]!=0)  ? abs(intval($_GET["w"])) : 25;
    $img_h = (isset($_GET["h"]) && $_GET["h"]!=0)  ? abs(intval($_GET["h"])) : 115;
    $img_t = (isset($_GET["t"]) && $_GET["t"]!="") ? $_GET["t"]              : "Ingen parametre";
   
    $img = imagecreate($img_w,$img_h);
   
    $img_bg = imagecreatefromgif("_img/button_bg.gif");
    $img_left = imagecreatefromgif("_img/button_left.gif");
    $img_right = imagecreatefromgif("_img/button_right.gif");
   
    imagesettile($img,$img_bg);
   
    imagefilledrectangle($img,0,0,$img_w,$img_h,IMG_COLOR_TILED);
   
    imagecopy($img,$img_left,0,0,0,0,imagesx($img_left),imagesy($img_left));
    imagecopy($img,$img_right,imagesx($img)-imagesx($img_right),0,0,0,imagesx($img_right),imagesy($img_right));
   
    $ft_size = 1;
   
    while(true) {
       
        $corners = imagettfbbox($ft_size+1,0,"arial.ttf",$img_t);
        $c_x1 = $corners[0];
        $c_y1 = $corners[1];
        $c_x2 = $corners[2];
        $c_y2 = $corners[3];
        $c_x3 = $corners[4];
        $c_y3 = $corners[5];
        $c_x4 = $corners[6];
        $c_y4 = $corners[7];
       
        if(abs($c_x3-$c_x1)<imagesx($img)-8
        && abs($c_y3-$c_y1)<imagesy($img)-8) {
            $ft_size++;
        } else {
            break;
        }
       
    }
   
    $corners = imagettfbbox($ft_size,0,"arial.ttf",$img_t);
    $c_x1 = $corners[0];
    $c_y1 = $corners[1];
    $c_x2 = $corners[2];
    $c_y2 = $corners[3];
    $c_x3 = $corners[4];
    $c_y3 = $corners[5];
    $c_x4 = $corners[6];
    $c_y4 = $corners[7];
   
    $x = intval(imagesx($img)/2 - abs($c_x3-$c_x1)/2 + 1);
    $y = intval(imagesy($img)/2 + abs($c_y3-$c_y1)/2 - 1);;
   
    imagettftext($img,$ft_size,0,$x,$y,imagecolorallocate($img,51,51,51),"arial.ttf",$img_t);
   
    header('Content-type: image/gif');
   
    imagegif($img);
    imagedestroy($img);
    imagedestroy($img_bg);
    imagedestroy($img_left);
    imagedestroy($img_right);
   
   
?>

Hvordan undgår jeg at de felter dukker op somme tider?