Question App to force games to run at particular sizes on screen?

[_dawn_chorus_]

Is there an app that allows you to select a certain amount of the monitor that a game will then recognize as the new border?
I have a massive screen and for some games I'd like them to only use like 70% of the screen.

So something like when you open a game in a lower res in windowed mode but being able to resize or pre-select a window size for it to do that in.

 

[Karadjgne]

Depends on the windowed mode. Regular windows mode will have a sizable border, don't need to change resolution for that, Fullscreen windows mode is borderless.

 

[hotaru.hino]

Most games don't allow you to resize the window arbitrarily in windowed mode. If you need an exact resolution, you could try making a custom resolution in your video card's control panel and use that.