Have a widescreen computer and your RollerCoaster Tycoon 3 game is not filling up the whole screen? You can imagine that you can change this setting easily within the game, but even with that the game will appear at a fixed 4:3 aspect ratio, instead of 16:9. There is a way to enjoy your RCT3 game in full screen by changing one line in one file.
Before proceeding, make sure RCT3 is NOT running. For Windows Vista or 7 users, type in “%appdata%/Atari/RCT3/” in the search bar found at the start menu to to your AppData folder. For Mac OS X users, press Cmd+Shift+H to bring up the Home folder, and then navigate to Library/Application Support/RCT3. Once there, two files should come up. MusicGenre.txt, and Options.txt. The file that you want to open and edit is the Options.txt file. When open, the first set of words you’ll find are “Resolution”, followed by two numbers. Those two numbers represent the width and height that the game will appear in. You want to match those two numbers with your current screen resolution of your computer to have RCT3 fill up your screen. For example, if your screen resolution is 1366 x 768, “Resolution 1366 768” is the text you’re going to use. Below is an image of what the Options.txt file looks like.
The highlighted area of the txt file is where you change the resolution that RCT3 will appear in. After hitting Ctrl/Cmd+S or saving the file, relaunch RCT3 and the game should fill up the screen.
Mac OS X Lion and later: The user Library folder got hidden by default, so to get to the Options.txt file, you will need to hold the option key, then click “Go” on the menu bar at the top. From there, you should be able to follow the path to the Options.txt file (thanks to Kevin in the comments below for this info!)