The goalPoint the upload-folder to a static subdomain to serve adaptive images, that can get cached.
WordPress Rewrite Rules
You can read more in detail about rewrite rules API at Christopher Davis site.
The how-to on adaptive-images.php
Those are the steps needed (just to make the Q complete):
- The HTML starts to load in the browser and a snippet of JS in the writes a session cookie, storing the visitor's screen size in pixels.
- The browser then encounters an tag and sends a request to the server for that image. It also sends the cookie, because that’s how browsers work.
- Apache receives the request for the image and immediately has a look in the website's .htaccess file, to see if there are any special instructions for serving files.
- There are! The .htaccess says "Dear server, any request you get for a JPG, GIF, or PNG file please send to the adaptive-images.php file instead."
The PHP file then does some intelligent thinking which can cover a number of scenario's but I'll illustrate one path that can happen:
- The PHP file looks for a cookie and finds that the user has a maximum screen size of 480px.
- It compares the cookie value with all $resolution sizes that were configured, and decides which matches best. In this case, an image maxing out at 480px wide.
- It then has a look inside the /ai-cache/480/ folder to see if a rescaled image already exists.
- We'll pretend it doesn’t - the PHP then goes to the actual requested URI to find the original file.
- It checks the image width. If that's smaller than the user's screen width it sends the image.
- If it's larger, the PHP creates a down-scaled copy and saves that into the /ai-cache/480/ folder ready for the next time it's needed. It and also sends it to the user.
How would I set up the rewrite rules to point a subdomain to the the uploads folder and vice versa?