What I do is similar, I figure out if the aspect of the pixels themselves ie width/height gives you the same value as you'd get for a known aspect ratio, e.g. 16:10, and then make the assumption that the ratio is in proportion and size accordingly. The only problem is, it is possible to have modes which are not in proportion in terms of aspect - e.g. my widescreen monitor has a 1024x768 mode which stretches to fill a 16:10 aspect. There's no way to tell other than through user input. Unfortunately Max doesn't tell you what the aspect ratio of the mode is, which would be really nice. There's probably too many differences in the display hardware to do it consistently.