You can have objects placed in a certain fashion so that if all of them are visible, it is determined that the resolution is the highest; if some are visible, the resolution is medium (1024x768); if very few are visible at once, then the resolution is low (800x600).
Something like this:
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xxxxxxxxxxxxxxxxxxxxxThe red "x"s would be where objects placed would be visible together only in the highest resolution; the blue represents objects placed that would be visible only in the highest or medium resolutions; the green would be visible in the lowest resolution. Of course, you don't need to place objects on every spot. The extents would do (e.g. the corners, the edges, etc.).
Then, you can use the visibility logic conditions (Object visible/not visible conditions) to determine what objects are visible. If all are visible, then the resolution is the highest. If some are visible, then it is medium. If very few are visible, then it is low.
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