Asynchronous game in real time

We made a game, a mobile racing game for Red Bull. Sort of in the trails of Chrome Racer, but even more fun we think. We used some cool stuff that we’ve written about here before – html5 audio, multiplayer gaming with websockets and node.js, but also stuff that was new to us, the vector scripting library paper.js, canvas animation and angular.js.

The first mindboggle was the question of where the race actually is taking place. The game is multiplayer and also a competition, so we needed to make sure the race synced well across multiple devices, but also that the game was correct in deciding who’s winning and what time you get. We started out with presuming that the game had to take place in real time on the server, and the server could push your car or hold it back when you got out of sync with the server, or crash it when you took a curve too fast, but in bad conditions with network latency the racing got twitchy. So the gaming experience hurt – no good.

Blue car is weirding out.

It was best to leave your car be. If your opponents get jittery on bad reception it’s ok, as long as your own car moves smoothly. So if the client is controlling the race, how do we know it’s not spoofing a killer race time? The conclusion was that the race must take place both in your browser and on the server, and the server rules when it comes to the actual result.

If the server doesn’t interfere with your driving it doesn’t have to work in real time either. There’s no clock running on the server so to speak. The server sets a start time, you tell the server when you’re throttling and when you’re not (or actually when you did throttle, due to latency we work with past tense data – the player throttled 0.2 seconds ago), and the server calculates the race, and where it thinks you should have crashed. Does nothing with this data, just quietly executes the race in an asynchronous manner. Since it just waits for events to come in it doesn’t really know or care where you are at this exact moment, not even at the finish line. Your race time is calculated when the server simulates your final run towards goal and sees that this gal was over the finish line at 16.34.

The server basically take your actions and recreates your race on the server piece by piece, while simultaneously sending out the same data to your opponents, and finally sets your race time with no consideration of the time you said you finished at. Latency matters at race start, if you’re on a bad connection you get a late start, but at the end and during the race it doesn’t matter at all. Your opponents will just look like drunk chinchillas on the race track.

Play the game on your phone: