mmo-snake
Massively multiplayer online snake. Peer to peer with CRDTs at core. MVS architecture with reagent and react for rendering.
Overview
- Largely an experiment
- Developing a better understanding of CRDTs
- Figuring out a good architecture for client side development
Design
Goals of a representation:
- Minimise communication between clients.
- Allow for errors to be identified.
- A message is dropped or arrives out of order.
- Is this actually a concern with tcp?
- Not cause compound issues in the case of errors.
- Probably not an issue with tcp either.
- Able to drop old states/messages if desired in order to only show the head of the snake.
- Be able to determine who 'knew' what in order to resolve winner in the case of actions frome each user causing death.
- Allow for predictive movement in the case of network latency.
- Allow for an unlimited number of players
Ways that you could structure the snake game:
-
(players-vector (moves-vector (map vector-clock action)))
{:alice [(action [10 8] :left) (action [11 8] :right)] :bob [(action [0 8] :right) (action [10 11] :right)]}
Here Bob has seen that Alice turned her snake left at T10. So if turning right caused Bob to crash into Alice then bob would lose. Bob also potentially crashed at T11, however Bob was not aware of Alices actions at T11 that could have caused him to crash into her.
Perhaps we allow snakes to cross in the case that there was no barrier that you were aware of at the time of collision. That still means that someone could 'pop' in front of you after a late message and their predicted position was incorrect.
Perhaps you have a kind of action that's just 'I am here' that gets fired every few spaces. Clients color predicted positions differently so that it's clear that they might be re-drawn.
It would be convenient if the coord at which you turned was included so that we could work backwards rather than needing to maintain some state from when you first started the game. Might also help with error checking.
-
(players-vector (positions-vector x-y-coord)) Have each client report death if they see their player crash. If not then just allow the overlap. Relies on trusting the clients. In the case of constant latency then the snake will be slightly behind it's actual position and will probably look fine. If you have a slow down in delivery of messages and then they all come together then the snake will jump forward after having stood still for a while. Will cause a lot of packets to be sent.
Setup
To get an interactive development environment run:
lein figwheel
and open your browser at localhost:3449. This will auto compile and send all changes to the browser without the need to reload. After the compilation process is complete, you will get a Browser Connected REPL. An easy way to try it is:
(js/alert "Am I connected?")
and you should see an alert in the browser window.
To clean all compiled files:
lein clean
To create a production build run:
lein cljsbuild once min
And open your browser in resources/public/index.html. You will not
get live reloading, nor a REPL.
License
Copyright © 2014 FIXME
Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.