Ever since Mari0 was released, people have been requesting the ability to run the game in fullscreen mode. I’ve always been against this since Mari0 uses a 400x224 base resolution which can’t be easily scaled for any resolution.
The solution is either: Change the base resolution by showing more/less blocks on the screen at the same time, something I can’t do because it would change gameplay, or scale the game with unrounded factors, but I really don’t like scaled pixel art.
I caved in though and added both letterbox and streched fullscreen to SE. You can chose any scaling factor that fits on your screen and going any further will make it go fullscreen. I put up a quick comparison between letterbox, which preserves the aspect ratio, and stretch, which fills up the whole screen, below.