PHP Grid Generator

generate_grid.php

<?php
/**
 * This script will generate a grid overlay for
 * a 960 style grid given three params, column_width, gutter_width, height.
 * and columns.  These will default if not provided. The result
 * will be a PNG file.  The height specifies the height of the image which
 * defaults to 1.
 */

$expires = 60*60*24*   30;
header("Pragma: public");
header("Cache-Control: maxage=".$expires);
header('Expires: ' . gmdate('D, d M Y H:i:s', time()+$expires) . ' GMT');
header("Content-type: image/png");

$column_width = 60;
$gutter_width = 20;
$columns = 12;
$image_height = 1000;

if ( isset($_GET['column_width']) ) {
  $column_width = $_GET['column_width'];
}
if ( isset($_GET['gutter_width']) ) {
  $gutter_width = $_GET['gutter_width'];
}
if ( isset($_GET['columns']) ) {
  $columns = $_GET['columns'];
}
if ( isset($_GET['height']) ) {
  $image_height = $_GET['height'];
}

$grid_width = $columns * ($column_width + $gutter_width);

$image_height = 1;
$image_margin = 0;
$image_width = $grid_width + $image_margin * 2;

$image = @imagecreatetruecolor($image_width, $image_height);
imagealphablending($image, false);
imagesavealpha ($image, true);

//$grid_column_color  = imagecolorresolve($image,255,229,229);
$grid_column_color    = imagecolorallocatealpha($image, 255, 255, 255,  60);
$grid_margin_color    = imagecolorallocatealpha($image,  74, 255, 255,  60);
$grid_colEdge_color   = imagecolorallocatealpha($image, 202, 127, 127,  60);
$background_color     = imagecolorallocatealpha($image, 255, 255, 255, 127);

imagefilledrectangle($image, 0, 0, $image_width, $image_height, $background_color);

$margin = $gutter_width / 2;

for ( $i = 0; $i < $columns; $i++ ) {
  $left_margin  = $i * ($gutter_width + $column_width) + $image_margin;
  $left_col     = $left_margin + $gutter_width / 2;
  $right_col    = $left_col + $column_width - 1;
  $right_margin = $right_col + $gutter_width / 2;

//print "col $i : $left_margin <br/>\n";

  imageline($image, $left_margin, 0, $left_margin, $image_height, $grid_margin_color);
  imagefilledrectangle($image, $left_col, 0, $right_col, $image_height, $grid_column_color);
  imageline($image, $left_col, 0, $left_col, $image_height, $grid_colEdge_color);
  imageline($image, $right_col, 0, $right_col, $image_height, $grid_colEdge_color);
  imageline($image, $right_margin, 0, $right_margin, $image_height, $grid_margin_color);
}

imagepng($image);
imagedestroy($image);

?>