Musings about FP and CS

A log of my journey through FP and CS

Fun with pong at Roland Garros

by Clement Delafargue on August 7, 2014

Tagged as: roland garros, company campus.

I worked on a fun project with Company Campus for the French Open Roland Garros.

The goal was to let people play Pong on the Suzanne Langlen court giant screen.

Pong Screen

Instead of playing with regular controllers, people just had to put a hand in the air. The paddle position was mapped to the hand’s position.

Game controllers

The hardware

It’s made of simple, easy-to-get parts.

The game server is a compact PC.

The screen is a 74m² 32/9 giant screen.

The game controllers are custom-made. Each one runs on a raspberry pi + an arduino card for data acquisition. The frames were made by welding steel bars and adding wood panels.

Both the game server and the controllers RasPis run on Archlinux. Everything is automated thanks to systemd (everything had to be plug-and-play). systemd services and network configuration helped me a great deal in making everything resilient (NodeJS applications have this weird tendency to not be reliable).

The code

We used johnny-five to get the data from the arduino.

The controllers stream the raw data from the ultrasound sensor to the game server, in UDP. The CPU and RAM are a bit tight, so nothing else is done there (switching from TCP to UDP and removing data normalization gave a huge latency drop).

The game itself is written in nodeJS with a HTML display. Since the pong physics are very straightforward, I was able to write it entirely in an evented fashion. No game loop, yay (even the ball movements are rendered with CSS transitions).

To normalize the data streamed by the controllers, BaconJS was of great help.

Here’s the code which removes the errors and transforms the raw position in centimeters into a relative position in a [0, 1] interval.


var normalizedPosition =
rawPosition
    .filter(function(p) { return p >= min && p <= max;})
    .skipDuplicates(function(op, np) { return Math.abs(op - np) < 1; })
    .map(function(p) {
        return 1 - (p - min) / range;
    });

Overall

This project was really fun. It’s rare to have the opportunity to do stick welding in my day-to-day job and to have your code displayed on a 74m² screen right in the middle of Roland Garros :-)

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