This utilizes the very old method Wolfenstein 3D used - albeit modified. It sends out n rays from the camera, and the distance they intersect with an object at, you draw a rectangle of width , and height corresponding to the distance. This creates the illusion of a first person view. The actual calculation method for determining intersection distance is different from the Wolfenstein 3D method - but the end result is visually identical.
You can change the view in the running program by pressing 'v'.
(This is not 1:1 with the above gif)
This project was inspired by this tutorial.