Xkcd HTML5

Canvas MMO

WebSocket

Scaling with

PubNub

by Stephen Blum

Hello all hackers. We notice a new MMO was released by n01se and xkcd yesterday (September

26th, 2012) with multiple users flying around with a balloon figure. If you got stuck, you can click your

balloon guy and turn into a ghost to seamlessly move through the landscape unhindered by mortal

barriers like trees and hills. There was a problem however with the scaling of users on the system.

The max concurrency could only be 20 users at a time leaving many wonder where the MMO part of

the MMO was.

Click here to join the live MMO game Powered by PubNub.

We saw an opportunity to save the day and scale using PubNub’s real-time cloud based global

infrastructure. This allows the concurrency to scale easily. Note that in order to do this in a short time

frame, we excluded some important security precautions. However we hope you play nice in this real-

time MMO that actually scales.

Game Instructions

1. Click to Move

1. Type to Talk

1. Press Enter to Clear

1. Type “I am YOUR_NAME” and Press Enter

Note that in order to switch from the non-

scaled Node.JS server to PubNub, we had to

come up with a solution to replace the server

side with a full 100% client side solution.

Therefore, we built an RFC 6455 WebSocket

Client that works with all users and

browsers. By doing this, you are actually

connecting to a PubNub Edge Node nearest

your location, creating a fast, low latency

connection. Now you can relax, sit back and

play a real MMO courtesy of PubNub.

Watch the video on the right to see xkcd

HTML5 Canvas MMO WebSocket Scaling with

PubNub in action.

Credits

1. Homage to n01se and xkcd, especially 1110.

2. No server required courtesy of PubNub.

3. RFC 6455 Support for WebSocket Client Specification Written by Stephen Blum.

4. Port from original author written by the PubNub Team.

5. Download/Clone Source Code Repository: GitHub Source Code.

As a follow up to this article, we wanted to note and proclaim our thoughts and feedback on the original source. Thank

you 1110 and n01se for the creativity and JavaScript. One thing we wanted to change was the animation style you

used for network coordinate relays. The Animation would animate based on Vectors and current X, Y coordinates.

However since the game had little interactivity between players, the better method would be something we at PubNub

are well versed in which we call Dead Reckoning with Deterministic Lockstep at a single step buffer. This method

prevents jitter and jumping of the avatars on the screen. If we were to upgrade the animation engine, we would

implement this method first. You can see this style of network tweening on our Home Page of PubNub.com click the

tab that says “PubNub In Action”. Looking forward to seeing you in the game today!