I'm developing a 2D HTML5 Canvas Game, and I am trying to think of the most efficient way to implement a Physics Loop on the server-end of things, running NodeJS and Socket.IO.
The only method I've thought of is using setTimeout/Interval, is there any better way? Any examples would be appreciated.
EDIT: The Game is a top-down Game, like Zelda and older Pokemon Games. Most of the physics done in the loop will be simple intersects.
I believe setTimeout is good enough for your needs. I am, myself, facing a similar situation and I am going with setTimeout.
This awesome article on BNG helped me better understand what a I have to do (or, at least, try): Real Time Multiplayer in HTML5.
About the link: It talks mostly about the multiple game loops and networking them. It's pretty cool. Below, an excerpt.
When it comes to a real time game, we want to run the game logic itself on the server AND the client. This is due to the fact that the server needs to be the authority on the state of the game at all times, but the client needs to run the game locally too. Each frame on the server, input from the network will be processed and applied to players, and that change is sent to the other players at a fixed rate. On the client, input will be collected and sent to the server, and positions can be updated while waiting for the messages to come back from the server (client prediction).
It's a highly recommended read. At least by me. =P
For server-side stuff you have a couple of options. The first is to entirely extrapolate all your collisions working off of the assumption that you will have frequent-enough messages from clients, communicating all meaningful state change through the server, which then will run validation on game events only as it receives IO callbacks from the client connections.
The second way, which you seem to prefer, is to run your own loop while whilst you process IO callbacks. Although setInterval and setTimeout will accomplish this, you have a much more fine-grained set of tools to control this: setImmediate(callbacks, [[arg], ...]) and process.nextTick(callback).
Process.nextTick will run your callback before other IO events, so long as you haven't stacked up a recursively infinite stack of callbacks (if it exceeds a certain number, process.maxTickDepth, then it will yield to the IO callbacks).
SetImmediateCallback is similar to process.nextTick in that it acts every tick, but only one of the queued callbacks gets executed on every tick, rather than all queued callbacks.
Using these will look similar to setTimeout or requestAnimationFrame.
function gameLoop() {
updateCollisions();
process.nextTick(gameLoop);
}
process.nextTick(gameLoop);
The advantage of these is that you're not dependent on V8's implementation of setTimeout and setInterval. These are more of a direct line to Node's event loop. Just be sure you don't starve the IO if you are using process.nextTick. updateCollisions should be guaranteed to not take that long at all.
