Faris Amer - Collision Sim

Pretty neat, right?

I used verlet integration to calculate the movement of the balls, an O^1 algorithm to calculate collisions with the stage, then an O^2 algorithm to calculate collisions with the other balls. I had to create custom Vector and Ball classes, and used native java packages for drawing and timing.

If you want to see my code, you can look at the repository at https://github.com/faris-amer/CollisionSim to view the full code. I'm pretty proud of myself for this one, I didn't follow any tutorials and just followed a few videos that covered collision detection conceptually, but never a full code rundown.

All the steps I followed to create the program, as well as a longer video of the full program running is below!

The first step I had to do was to create a stage, somewhere for the simulation to take place. For this, I just used basic java.awt methods and created a flat gray background and a white circle inside.

Next, I created a Ball object, drew it, and added gravity to it. Something's off though... It seems to be passing straight through.

Now, we add some collision code that keeps the ball in the stage, that goes as follows:

There are many optimizations I could make to this code, but for a first-time experience with this world of collision, I think it works pretty well.

Now, what happens when we add more balls? ..not much, at least not yet.

Doing object-object collision took me the longest, but I devised a method to make it work, albeit not in the most efficient way, but it works for the purposes of this simulation.

A little bit of tinkering later... and we've got working collisions!

Now, if the code is a little hard to read, I've illustrated below how the collision detection works.

When a ball is created, it's added to a list of balls, which the solver loops through every tick. So it's comparing every ball to every other ball one by one to see if any collisions are detected, as such:

Balls aren't touching, nothing is done.

Now the balls are touching, so it executes the code.

(normally this wouldn't show, but I've slowed the code down for visual purposes)

The program creates two vectors, then....

The program 'pushes' the two balls apart in the direction of the vectors.

Tada!

Now, we've seen what happens with 3 or 4 balls, what happens if we add... a LOT more?

Our stage starts to resemble a popcorn bucket, and our balls go a little wild.

By adding a simple loop to sub-step our code (do multiple collision calculations per frame), we get *much* smoother collisions.

And that's it! Adding a few more lines of code to color the balls, make them different sizes, and spray them from the middle, we get a nice show of what the program is capable of.

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