Wii Darts: Powering Ajax applications with Wii controllers
Date : 2008 05 07 Category : Tech & Development
AjaxianBen and I gave a presentation at JavaOne on what’s new with Ajax. Since this was JavaOne, we skewed a little more than we normally would to Java topics, and one of them was using the new Java Plugin, that has great new features such as being able to take a running applet out of the web page, and having it continue to live after shutting down the browser. Java is running out of process here, which also helps the “Java crashing the entire browser” problem.
Anyway, back to our demo. For some context, last year at JavaOne had us performing Guitar Hero on stage, so we knew that we had to use a gaming console in some way. This year it had to be the Wii, but instead of using the console, we decided to just use the controllers.
Wouldn’t it be cool to control a Web page using the controllers? We thought so, and we set to it. You can talk to the Wiimotes via Bluetooth, so we needed a stack that would allow us to do just that. Java has a bluetooth stack. We could get an applet to talk to the Java stack. Hmm.
It actually took quite some time to test out the various stacks out there. In the end we went with a native system called Wiiuse that a lot of Wii hackers use. There is a wrapper library called Wiiusej that gave us exactly what we needed.
A quick test later and we had an application that was talking between the remote and the program. It turns out that the main controller sees a series of IR lights that are in the Wii sensor bar, and this allows you to simulate the system with any decent IR source. In the presentation room the big lights that shine on stage were strong enough to act as a sensor bar so we won’t even have to use it. We can just point out to the crowd.
Anyway, back to the application. We then wrote a Java class that acts as a state machine for what the remote is doing. It understands the movements, which buttons are pushed, how fast you are moving the device. With this data we could build a simple darts game. With the state machine Java code, and an Applet wrapper that exposed the information, we were ready to get to the Ajax side of the house.
We painted a darts board onto the screen and then had JavaScript start polling the Applet for information via JSObject (As simple as: document.nameofapplet.pollmethod()). This turned out to be more stable than talking the other way, even though it meant we were polling instead of being entirely event driven. When the JavaScript code polled the applet it would pass back a data structure with the data for the coordinates of the remote, and whether the dart had been fired (button A to fire, button B to reload). We would move the dart image on the screen as you move the remote, and when fired we kicked off an animation to fire the dart at the board.
At first, it was all too simple. You setup the shot and it would get the right area every time. Not a fun game. We then decided to add some simple physics to the Ajax game. We took into account the velocity of the throw (if weak it would fall down) and how straight your shot was. If you wiggle around, the dart will not be accurate.
Anyway, this was a lot of fun, and shows that as much as we mock Java applets, if we forget about using them as fancy blink tags, and instead think of them as more extension points, maybe there is life for them.
The video below shows you a demo of the application, the source code with an explanation, and more details.