The Bear Cannon

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By Brent Rossen
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01.11.2007
Download Project - 25 MB (no source, no working files - large audio file)

The Story
You've been called out of the audience in "The Big Tent" to assist the ringleader with his demonstration of "The Flying Bear!" Aim the cannon carefully and fire the bear through the hoops. Make it through all 5 hoops and you win!

Setup Instructions
Print the markers from the zip file, I used the L (tracking head), Kanji (tracking Cannon), and sample2 (tracking Lighter). Set up webcam as usual for artoolkit. Be sure you're at least 3 feet from the screen so that the webcam can see all three markers at once and you can see the cannon. Run BearLaunching.exe to start. Turn on your audio, you should hear a welcome then some music.

Interface Instructions
Using the Kanji marker, aim your cannon by moving the marker horizontally across the camera view, this will rotate the cannon. Use the sample2 marker to control the Lighter, the movement is the same as the cannon. Touch the Lighter to the wick on the top of the cannon to fire. The bear will fly out of the cannon in the direction you are aiming.
Be aware that if you move the lighter to the wick, then move the sample2 marker out of scene, you will fire continuously. Since controlling three markers at once can be difficult with AR Toolkit you can also fire by pressing the 'a' key.
The interpupillary distance can be adjusted with + and -.
Also note that the "you win" is the end of the game, you can keep firing the bear, but nothing else happens.

Project Notes
This game was chosen in large part because I wanted a scenario where the stereo would actually make a difference. It is significantly easier to aim the cannon when you can look down the barrel towards the target (given by head tracking), and it makes it significantly more immersive that you have to change your focus to look at the distant objects. In this way stereo doesn't just look "better", it actually enhances performace in the system. The disadvantage of the red blue stereo is that it's much more difficult to see the details.
Collision detection was used to determine when the Bear passed through a hoop as well as when the lighter touched the launcher.
The bear flys in a parabola out of the cannon, much as it would in a vacuum. No friction or acceleration was taken into account. Simplified physics was enough for the game to be fun.
Since the rotations in artoolkit are imprecise the rotations of the objects are determined by the translation of the markers.
All of the vocal sounds were made by me. The children cheering and the cannon were found at findsounds.com. Thunder and Blazes was found at Wurlitzer 165 Sound Files.
FMODex was used to play sounds. I chose to use an audio feedback system because I thought it would be more immersive.
All objects were made by me.

Time Worked: ~40 hrs