What Optimizations Does A Browser Perform When A DOM Element Is Being Rendered Off Screen?

I control an iframe being rendered on another domain. Is there a clear way of telling whether this iframe is being rendered above or below the fold on the parent page? Obviously, I

Solution 1:

I don't think so.

The same origin policy restriction prevents that, although you can use url parameters, which can be set by the javascript embedding the ad, to the offset on the page.

Solution 2:

This really varies by-browser, as different browsers interact with the Flash plugin differently. The most precise explanation I could find is on an old connectedpixel post.

At the point of writing, Firefox didn't init a flash object until it was scrolled on page. IE, on the other hand, resized the Stage element when it scrolled into view. No versions of browser, Flash, or OS are given, so this may have changed since that test.

In short, I need to make a flash object and play with it, watching for various events.