Is it because you're drawing to integer coordinates and not antialiasing your lines? If the boxes are not actually overlapping, as in hires, then even the lowres presumably should show some trace of the white of the larger box blended in with the red of the smaller box, all within one pixel. That you have total overlap of red replacing white suggests you aren't drawing properly.
Everything is modelled with floats, of course, but they have to be converted to integers at render time (i.e. pixel coords). Anti-aliasing doesn't come into it as there isn't any - this is pure 2D. I absolutely would not do this as you're essentially allowing users with different screen resolutions to inhabit different worlds -- it will bite you on the ass eventually.
Assuming that collisions are bad for the player (as they usually are), there visually appearing to be a collision where there actually isn't one will do nothing more harmful than give the impression of squeezing past something by a hair's breadth. Every shooter with hotspots does this and I wouldn't worry about it.
Indeed - some good points. I have decided to stick with using the mathematical representation and just leave it to the renderer to display the world as accurately as it can. I have yet to see a visual error of > 1 pixel so it should be fine.Assuming that collisions are bad for the player (as they usually are), there visually appearing to be a collision where there actually isn't one will do nothing more harmful than give the impression of squeezing past something by a hair's breadth. Every shooter with hotspots does this and I wouldn't worry about it.
Thanks.