This totally misses the point. I can't run all those calculations while rendering a website. The browser needs to be intelligent enough to not dynamically jump around in the viewport when an element finished loading. Just fix the viewport and attach at the top and bottom.

And relative units don't fix this either as that information still misses the ratio of my image. If it's 100 vw, how high is it? I don't know this information without fetching the image, doing calculations and dynamically updating the DOM with that information.