I have a problem with the windowed mode. It will scale to the actual resolution, thus giving me a 20fps or so. I want to have the resolution set in the game (like 1280×800), but upscaled into the window size.
So … it would give a (more) blurry picture, than the native resolution (obviously), but I would get a faster gameplay, and windowed gameplay functionality. I could change songs in my music player with ease, respond to my friends on Skype/MSN/Steam/XMPP/whatsoever.
Best Answer
I think I understand where you're coming from here - you want the game to run in windowed mode, but cover the entire screen, at a resolution lower than what you normally run Windows at.
If this were possible, it would have to be a feature of the game or your graphics driver. I've checked all of my graphics drivers on various systems and not really seen this as an option. I don't own BF3 on PC (however, I played the beta), but I've not seen this as a game option anywhere previously either. The closest I've seen is using -window -noborder on Source engine games, which isn't exactly the same.
There is a similar option in Modern Warfare 3:
That said, you might be able to approximate this by changing your Windows desktop resolution before you load the game. Then play the game in windowed mode at the lower desktop resolution.
Alternatively, since the problem with running in your native resolution is that the frame rate is too low, you might consider messing with the settings to see if you can't boost your frame rate by compromising graphical quality.