As part of my new job and my thesis I researched and implemented a 2D version of GJK (Gilbert-Johnson-Keerthi), a useful and fast collision detection algorithm. I will attempt to explain its operation and provide a basic implementation that is consistent with the excellent presentation found at MollyRocket (link provided below) as well as providing an explanation of what one does after detecting a collision using GJK.
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I spent a long time doing this recently so I am going to make it as simple as possible. The first and most important step is:
IGNORE ALL THE TUTORIALS ON THE WEB.
People want you to set up Eclipse to look for X11 binaries, or to install stuff with MacPorts, etc, etc. TERRIBLE. Do this instead.
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After a night out celebrating a friend’s recent departure from work for Costa Rica and surf heaven, I stumbled back to MindTribe to play with my MBED, “a tool for Rapid Prototyping with Microcontrollers”. It’s actually a wonderful little device and I got this “persistence of vision” trick working pretty quickly. I taped the MBED, a Hall Effect sensor, and a column of LEDs to my bike wheel and spun the whole mess, using the MBED to turn the LEDs on at the right time to spell the little “J” you see in the video.
The “J” is painted a column at a time, but the column of light is traveling around the wheel, and because it happens so quickly, your eye smears all the light flashes together so it appears as if the “J” is being painted in its entirety at a single moment in time. This is persistence of vision.
You can buy much fancier setups from adafruit but I’m pleased with how this has turned out. The fact that I was able to bang this out in just a few hours after a few drinks is testament to the excellent development tools from the MBED team. I’ll keep working on it and see if I can come up with anything worth another blog post!