Created by Ricardo Cabello aka Mr.doob, Multiuser Sketchpad is an online sketching pad in your browser allowing many users to draw simultaneously. Having heard people talk about node.js on Twitter, Ricardo was interested to see whether he could apply it to his Harmony project. Node.js is a tool to provide an easy way to build scalable network programs. Many client connections can be handled concurrently allowing each connection only a small heap allocation. The first implementation of node.js by Ricardo allowed approximately around 100 simultaneous users where now, Ricardo has mentioned at least double that number.
Ricardo writes:
At this point is when you just need to sit down and get the thing working. Once it was working locally I got a slice in slicehost and in a matter of minutes the experiment was live. Considering that it costs $20 for 150gb of BW and that I received €60 from flattr last month I though it was worth spending that money on this project. (EDIT: At this rate I suspect I’ll end up spending the full €60 on this…)
The first version of the code was pretty much brute force, every user was sending their X,Y position every time they moved their mouse. Yes, that’s *a lot* of data per second. There has been 50gb of data transfered in just 4 days :P However, yesterday night I finally got a bit of time and improved a bit the data that gets transferred, and not only it consumes less bandwidth, the server’s CPU is much happier (btw, thanks sole for the top tip :D).
What is especially interesting about the project is user interaction. Where most people would try to contribute to each others’ drawings there are inevitable a few who always try to make this difficult. Luckily (from my recent chat with Ricardo), Mr.doob is on the ball so expect to see more features such as dedicated rooms + more..
As expected, people like to draw male reproduction organs all over the place, and an annoying one was people scribbling on top of nice drawings. It was so annoying that I even had to tweak the brush algorithm to discourage such actions. The faster you move the cursor the less opacity the pencil has. Stupid solutions for stupid problems.
The most interesting case was “Talentina”, which I suspect is a little girl. She seemed happy and was drawing cute things like a giraffes and so on, but then someone will arrive and draw a penis on it. She would move the cursor away, like looking from the distance, and move away like in a slow/sad pace…
Read the full post about the project on Ricardo’s blog.
Also, don’t forget to grab the Mac OSX ScreenSaver version of Multiuser Sketchpad available here and created by Cédric Raud.
(Screenshots by Simon Strandgaard)
