This blog has a rotating header — if you visit /header/ and bounce on reload, you’ll see a series of random images. Here’s how it works:

The header is added to a div with the following CSS:

#headerimage{
  background: url("/header/") center center no-repeat;
}

/header/ is a directory in ~/public_html/. It contains a bunch of similar-sized images, along with the following index.php file:

<?php
$pattern = '/\.(png|gif|jpg|jpeg|svg)$/i';
$dh  = opendir('.');
while (false !== ($filename = readdir($dh))) {
  if (!is_dir($filename) && $filename[0] != '.' && preg_match($pattern, $filename)) {
    $files[] = $filename;
  }
}
closedir($dh);
$file = $files[rand(0, count($files) - 1)];
header('content-type: '. mime_content_type($file));
readfile($file);
?>

It’s pretty simple. It

1. looks for image files in the same directory (lines 2-9)
2. chooses one at random (line 10)
3. sets the mimetype of the response based on the image’s filename suffix (line 11)
4. sends out the file’s contents (line 12)

What’s nifty is you can turn this into an ultra-lightweight slideshow by adding one line:

header('refresh: 5');

after line 11 (the mime_content_type header). There isn’t any transition between the image changes, but we’ll leave that for next time.

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