Set screen resolution

[swanlon]

When screensaver starts from for example a game with stretched res resolution, the screensaver will turn on and only cover part of the screen (because it thinks my resolution is the stretched one and when it starts it minimizes the game, moving me to 16:9 res)

I'd like an option just to set the preferred screen res so doesn't matter what I am using as a screen res, it will always fit my screen.