Timthumb and Ajax

Posted by & filed under Ajax, Javascript, PHP.

Timthumb is a great tool for cropping/resizing images dynamically at the time the page loads. But what if you want to update the src of an image tag with a new image, for example, in an image carousel?

You can use timthumb via an ajax call, but the resulting data is binary so you have to do two things: 1) convert the binary to base64, 2) add a prefix to the src attribut it to tell the browser how to handle it.

So converting the binary data to base64 is done inside the timthumb script. What I did was check for a param in the GET and, if present, I converted the data to base64. In the timthumb serveCacheFile() function I replaced these line:

$imageDataSize = filesize($this->cachefile) - (strlen($this->filePrependSecurityBlock) + 6);
$this->sendImageHeaders($imgType, $imageDataSize);
$bytesSent = @fpassthru($fp);

with this:

		$imageDataSize = filesize($this->cachefile) - (strlen($this->filePrependSecurityBlock) + 6);

		if (isset($_GET['marko'])){
			// Look out for the 'marko' flag. This is serving a base64 encoded string so
			// that an HTML image tag can display the file in it's src attribute. Useful
			// when Ajax is needed to resize files for a carousel.
			$fsize = filesize($this->cachefile);
	        $binary = fread($fp,$fsize);
	        $bin64 = base64_encode($binary);
			echo 'data:image/bmp;base64,'.$bin64;
			return true;
		} else {
			$this->sendImageHeaders($imgType, $imageDataSize);
			$bytesSent = @fpassthru($fp);

Then in my HTML page I have a bit of jQuery as follows:

	load_link = encodeURI('&src=' + link + '&h=194&w=263&marko=1');
	$.get('/images/timthumb.php', load_link, updateLink);

	function updateLink(data) {

Where the ‘link’ var is the external file, in my case, a flickr hosted image. You can see I’m passing marko=1 in as a GET param. This is my flag that I pick up in the timthumb.php script. The function updateLink() adds the base64 encoded data to the src of the image with id flickr-first-photo.

One Response to “Timthumb and Ajax”

  1. Rob Anderson

    Thanks Mark, very useful (once I worked out the code samples you posted are a bit mangled with url encoding!).

    Cheers, Rob


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