Simple bar graph using GD and PHP

This is a simple piece of code to display a bar chart in PHP using GD with a 3D effect, based on the other bar chart code.
<?php

        

        // This part of the code is the same as the other 

        // graph example

        

        $values = array("23","32","38","57","12",

                "4","36","54","32","15",

                "43","44","30");

      

      $columns  = count($values);

      $width = 200;

      $height = 100;

      

      $column_width = floor($width / $columns) ;

      

      $padding = min(max($padding,1),$column_width);

      

      $im        = imagecreate($width,$height);

      

      $r         = 0xaf;

      $g         = 0xaf;

      $b         = 0xaf;

      

      // Create the colors.

      

      $gray      = imagecolorallocate ($im,$r,$g,$b);

      $gray_lite = imagecolorallocate ($im,$r+40,$g+40,$b+40);

      $gray_dark = imagecolorallocate ($im,$r-20,$g-20,$b-20);

      $white     = imagecolorallocate ($im,0xff,0xff,0xff);

    

      imagefilledrectangle($im,0,0,$width,$height,$white);

      

      $maxv = 0;

      

      // The first change - we need to reduce the maximum height

      // of the columns to allow for the vertical effect.

      

      $max_height=$height - $column_width;

      

      for($i=0;$i<$columns;$i++)$maxv = max($values[$i],$maxv);

        

for($i=0;$i<$columns;$i++)

      {

    $column_height = ($max_height / 100) * (( $values[$i] / $maxv) *100);

      

    $x1 = $i*$column_width;

    $y1 = $height-$column_height;

    $x2 = (($i+1)*$column_width)-$padding;

    $y2 = $height;

      

      // Draw the main columm

      

    imagefilledrectangle($im,$x1,$y1,$x2,$y2,$gray);

      

      // This is the offset for the 3D angle

      

    $offset = ($column_width-$padding) / 2;

      

      // Create an array for the top part of the column

      

    $pt = array($x1,$y1,

                $x1+$offset,$y1-$offset,

                $x2+$offset,$y1-$offset,

                $x2,$y1);

      

      // Now draw it.

      

    imagefilledpolygon($im,$pt,4,$gray_lite);

      

      // Create the side of the column

      

    $pt = array($x2,$y1,

                $x2+$offset,$y1-$offset,

                $x2+$offset,$y2-$offset,

                $x2,$y2);

      

      // And draw that part too

      

    imagefilledpolygon($im,$pt,4,$gray_dark);

      

      }

      

      // return the image using imagepng or imagejpeg.

      

      ?>