Games [4 Health] Jam 2012 – Public Play


Public Space Invaders @ Dutch Design Week 2012

During the Games [4 Health] Jam 2012 I helped develop the game Public Space Invaders as part of PowerTrippers. Since the theme of this game jam was Public Play, we emphasized on step-in/step-out gameplay where your body becomes the controller by moving around the playing field. By using the concept of Space Invaders, we try to capture simple and intuitive gameplay, as well as make it attractive for all ages. It proved to be mainly attracting young players (children and students) to actually play, and adults would play as well if their children wanted them to. People easily started playing and just as easily stepped out to go on with their usual business, and it was very pleasing to see many different ways of play happening; some would be sprinting from one edge to the other, while others where more focused on aiming as well as possible.



As a player, you control a spaceship that automatically shoots at invaders, and you move your ship around by moving inside the playing field. This is what happens while you’re a defender at the part of the playing field that is closest to the screen. When you move back a bit further, you turn your ship into a spy and stop shooting. However, you can push the invaders around to make them fly into bullets shot by other players. Since this is meant to be played at a public place, such as a train station, a big hall or at a park, Public Space Invaders has to be constantly running, even when no-one is playing. This is why you can only increase your score, and there is no way to lose points. Instead, the idea is to get the score as high as possible before the day is over and get your spot on the leaderboard for all places Public Space Invaders is installed.


We also created a versus mode, because we noticed everyone wanted a turn at shooting as the defender, but there was limited space. It also felt restricting to have to stay in that small strip in order to be able to actually score points, while you’d have a ton of freedom playing as the spy. It makes for some extra entertaining gameplay because everyone would be running around, between each other and you could swap teams instantly by just walking up into their respective territories (top would be red, and bottom would be blue). It wasn’t as inviting to play as the co-op, because it lacked the invaders you could interact with as a spy or defender in co-op, yet it made up for that by giving all players more freedom and the ability to score points.

Building the game

Basic construction PSI

In order to be able to track player movement, we needed a camera at a high enough position so it can see as big an area as possible. The bigger that area, the bigger your playing field. About 5 meters high is the minimum in order to get a decently sizeable field. Next, we needed software that could actually register these people. This was the part I was working on after concepting as a group, and I found a piece of software online that was free for us to use, and it’s compatible with Unity. This is OpenTSPS, available here:  Basically, it makes a snapshot of the background you wish to track people’s movement on (like the floor or a wall) and it compares that background with the images it gets from the camera. Then it registers all differences with the background and turns them into objects with information like their position and size, and sends that to any application listening. The process will look a little bit like this:



actual image

Actual image







Tuning OpenTSPS and the setup were mainly my tasks, together with whomever was free at those moments. We all had an equal say in what the game would look and feel like, so concepting was a real team effort. We were very happy to be one of the five teams to be able to present our game at not only the Games 4 Health Europe Conference 2012, but also at Game in the City in Amersfoort, the Dutch Design Week in Eindhoven, and at my school Fontys Hogescholen Eindhoven.

Public Space Invaders trailer at the end of the Games [4 Health] Jam 2012