I used SFML which is a simple library for working with the system, graphics, audio, etc. I used the mouse position and subsequently the window position to decide what part of the game world I want to show, and rendered only that part in the window. It took a while to get right because my math was not great at first lol, and it would've definitely been easier to use something like raylib which supports transparent windows so that I could make a virtual fake window. I mostly just wanted to try not to use a game engine for a jam (and also do something cool with desktop windows). Thanks for playing!