Game Dev - Do you need an additional web server?

I'm a software developer who is now coding for blockchain. I learned Web3 but I want to move on from utility apps to making a game. I have found lots of tutorials online, but the one question I can't seem to find the answer to:

Do you need a separate web server (beyond the frontend host and storing data in smart contracts) to process the game logic/physics/etc?

Ex. If I wanted a character to buy a potion from a shop, that seems straightforward, just make a purchase request and store the result in a SC variable, but what about something such as collision detection? If my character needs to walk to the right until they hit a wall, how do I check if there's a wall there every step of the way? It seems prohibitive to make a SC read call every step they take and you certainly can't allow the frontend to determine... well, anything really, when money is at stake.

Thank you for any information or just a point in the right direction!