Show HN: Easel – Code multiplayer games like singleplayer

For the past 3 years, I've been creating a new 2D game programming language where the multiplayer is completely automatic. The idea is that someone who doesn't even know what a "remote procedure call" is can make a multiplayer game by just setting `maxHumanPlayers=5` and it "just works". The trick is the whole game simulation, including all the concurrent threads, can be executed deterministically and snapshotted for rollback netcode.

Normally when coding multiplayer you have to worry about following "the rules of multiplayer" like avoiding non-determinism, or not modifying entities your client has no authority over, but all that is just way too hard for someone who just wants to get straight into making games. So my idea was that if we put multiplayer into the fabric of the programming language, below all of your code, we can make the entire language multiplayer-safe. In Easel the entire world is hermetically sealed - there is nothing you can do to break multiplayer, which means it suits someone who just wants to make games and not learn all about networking. I've had people make multiplayer games on their first day of coding with Easel because you basically cannot go wrong.

There were so many other interesting things that went into this project. It's written in Rust and compiled to WebAssembly because I think that the zero-download nature of the web is a better way of getting many people together into multiplayer games. The networking is done by relaying peer-to-peer connections through Cloudflare Calls, which means Cloudflare collates the messages and reduces the bandwidth requirements for the clients so games can have more players.

I also took inspiration from my experience React when creating this language, here's how you would make a ship change color from green to red as it loses health:

`with Health { ImageSprite(@ship.svg, color=(Health / MaxHealth).BlendHue(#ff6600, #66ff00)) }`

There is a lot of hidden magic that makes the code snippet above work - it creates a async coroutine that loops each time Health sends a signal, and the ImageSprite has an implicit ID assigned by the compiler so it knows which one to update each time around the loop. All of this lets you work at a higher level of abstraction and, in my opinion, make code that is easier to understand.

Speaking of async coroutines, my belief is that they don't get used enough in other game engines because their lifetimes are not tied to anything - you have this danger where they can outlive their entities and crash your game. In Easel each async task lives and dies with its entity, which is why we call them behaviors. Clear lifetime semantics makes it safe to use async tasks everywhere in Easel, which is why Easel games often consist of thousands of concurrently-executing behaviors. In my opinion, this untangles your code and makes it easier to understand.

That's just the beginning, there is even more to talk about, it has been a long journey these past 3 years, but I will stop there for now! I hope that, even for those people who don't care about the multiplayer capabilities of Easel, they just find it an interesting proposal of how a next-generation game programming language could work.

The Editor runs in your web browser and is free to play around with, so I would love to see more people try out making some games! Click the "Try it out" button to open the Sample Project and see if you can change the code to achieve the suggested tasks listed in the README.