Tuesday, June 26, 2007

Addendum II

One area of Armadillo Run that I did not cover in the book is spectator levels. The AR home page hosts several hundred of them, and perhaps a few more can be found around the Internet. DEVEREX's gigantic roller coaster levels are classic and some of my favorite spectator levels.

The following picture shows the spectator level "Counting to Four". I created this counting machine using bidirectional switches and a cloth-chain elevator. It counts to four, repeats, and then stops.
It is fun to break new ground and turn ideas into working machines.


A spectator level can be made to automatically display following completion of a normal level, and this is commonly called a movie. To change a spectator level to a movie the spectator level's name must be changed to the normal level's name but with a ".end" extension:


Friday, June 22, 2007

Final Copy

After more crashes with Word, an additional 80 style and graphics changes, and wrestling with lulu.com's upload interface the book is published. Horray! I'm really tired now, and ready to get some sleep.

Monday, June 18, 2007


After over 100 little corrections, I no longer trust my ability to proofread anything :-P. If that were not enough, Microsoft Word probably crashed on me 10 times, causing me to go back and do some of the same corrections three times. Now I am waiting for one final proofreading and then I am done :-). What a relief.

Wednesday, June 13, 2007

Mother knows best?!

Yes, it is true :-). My mom has done professional copyediting before, and passing the book by her is a no-brainer. I have in front of me copy of the book with approximately 30 corrections to make in just the first 22 pages. Mainly little stuff, no big deal. I hope to get the rest of the corrections late this weekend.

Saturday, June 9, 2007

It's Here!

I finally received a copy of the book =). It looks like a large slick brochure rather than a paperback. This was the recommendation from lulu.com, as having under 70 pages in a paperback book makes the binding wear out faster. It looks like it will hold together over time. If anyone wants a hard cover version let me know and I will add that option.

A few images need work but it looks nice overall, just a few pixelated artifacts here and there. Next comes proofreading, that is after my finals Monday and Tuesday.

Oh, I forgot to add something to the last post on simulating drag. Drag on objects that are directly behind other objects is really complicated. It could be like a flock of geese where the lead object experiences more drag. Alternatively it could be like a plane getting caught in the turbulent downwash of another plane flying directly ahead of it. Drag seems potentially
like a big mathematical burden, even for a fast computer.

Wednesday, June 6, 2007

Simulating Drag

One thing the book only touches on briefly is how drag, a.k.a. air friction, is simulated in Armadillo Run. I have been thinking about this and realizing how complex drag is to simulate.

If your dealing with a
dense object moving at low speeds, like a rolled up armadillo for instance, drag is proportional to velocity. Armadillo Run uses this approach for its drag calculation each time slice, and it works just fine.

Unfortunately having drag proportional to velocity becomes increasingly inaccurate as an object approaches terminal velocity. Near terminal velocity drag (typically) increases proportional to the object's speed squared. On the other hand a sphere's streamline quality makes it a bit different than something like a box moving through the air. I once read the drag measured on a golf ball ended up being roughly proportional to the ball's velocity to the power of 1.3. Golf balls have evolved to minimize drag, though I suspect the spherical shape plays a major role.

The orientation of a moving object effects drag enormously. For instance a real metal sheet falling parallel to the ground will experience a much higher drag force than a metal sheet falling perpendicular to the ground. If the metal sheet were spinning it would experience a rotational drag force, and this would continually decrease angular velocity. Lift forces occur as well making the math even more involved.

Every complication adds to the CPU work required to calculate the next frame. An extremely accurate simulation would have a more limited number of objects that could be simulated and still have the program run in real time. Hopefully in the next Armadillo Run update Peter will find a nice trade-off between speed and accuracy for drag.

Monday, June 4, 2007

Still waiting...

After playing hurry up and wait I have a confirmation from lulu.com that my draft has been sent. Yay! Now I expect to release the book in under two weeks.