## A Eureka MomentMay 1st, 2009 Patrick Stein

I was pondering the Phony Physics again as I set to work on my iPhone app.

In the previous post, I twiddled the equations for damped spring motion until I found something visually pleasing. Last night, I went back to the drawing (a.k.a. white) board.

What if I used an exponential spiral (parameterized by arc length). Then, I could easily adjust the number of times it bounces back and forth. I could use a spiral like $r(t) = \alpha K (1-t)^n$ and $\theta(t) = K(1-t)$ where $K$ is some multiple of $2\pi$. Then, I could walk along the spiral getting to the origin when $t = 1$ going around the origin $\frac{K}{2\pi}$ times in the process. If I follow the curve at a fixed rate, then I guarantee that my oscillations will pick up speed as I approach the origin.

Rather than have it spiral into the center, I am just using the x-coordinate of the spiral as my new $t$ value to interpolate with. I like the effect for the most part. It overshoots a little bit far on the first oscillation. I may tweak it some more before it’s all over. For now though, I am sticking with it.

I will post some graphs soon.

## Sneak Peak: Artwork for Spelling iPhone AppMay 1st, 2009 Patrick Stein

My first iPhone app is a children’s spelling game. Development is coming along well now that I’ve discovered cocos2d-iphone. I should have screenshots to show early next week. For now, here is a sneak peak at one of the cards in the game.

## First decent images from my new raytracerSeptember 25th, 2008 Patrick Stein

Some time ago, I wrote an n-dimensional raytracer in C++. It does a fair number of things, none of them efficiently, most of the rigidly.

There are a bunch of things that I wanted to do with it for a long time, but it’s been too slow and rigid to make any of those things fun.

Enter Lisp. As soon as it made it through my skull that Lisp is actually compiled (honest-to-goodness your-CPU instructions), I wanted to rewrite the whole thing in Lisp. I have finally gotten started on doing that. And, I just made it to the point where I’m actually tracing rays. Here is a stereo pair of a three-dimensional scene: