In 1992, Wolfenstein 3d was announced, a completely different work from its series predecessor that shocked the world.
For the ultimate 3D effect, Carmack utilized the Ray Casting method in Wolfenstein 3D. It can greatly reduce the number of calculations, but the limitation is that the angle of view can not up and down, there is no concept of vertical height, and there is only a 90-degree angle between walls.
In fact, it wasn't really 3D, but a pseudo-3D effect. But in those days, it had a huge visual impact - people knew for the first time that games could be played like that!
Wolfenstein 3D was an eye-opener. The game environment and character models were impressive at the time, and it was much smoother than any 3D shooter that had come before it. This effectively popularized the shooter and made it accessible to everyone.