Heya. I'm working on some ideas for a 3D engine, and I made a function that rotates Matrixes. The actual Matrixes are structs which are passed to the functions via an array reference.

Well, one of the matrixes is a translation matrix, which moves points in 3D space. 3D Units in my engine are represented in what I assume is 10x3 fixed point. IE, 1000 = 1.000, 500 = 0.500, etc.

To do this, each matrix is multiplied, then all members are divided by 1000. When I express a translation by 2000 3D units, it is actually translating the matrix by 2,000,000, which comes out to 2000 after the division by 1000.

Anyway. After translating by 2,150 units, the 3D model begins to decrement negatively. I was wondering what was causing this, so I created a "more-difficult-than-it-needs-to-be" logging function that will quickly log up to 12 megs of matrix multiplications in seconds.

I have a picture of this log and the offending line when the translation multiplication returns a negative number.

What causes this? Is it because the Verge3 integers wrap to negative when they increase too high?

[click for image]

How does 1000 * 2150000 = -2144967296?

(replaced image with link. -Grue)

I'm somewhat surprised about the number of times this question comes up. I thought the wrapping behavior of signed integers was well known amoung programmer circles.

I am open to suggestion about where best to put it. Appendice? New section somewhere else?

Sorry, I knew about how the variables wrapped, but I had no concept of at what value they wrapped.

I understand wrapping and signed integers, I just don't know their max values. Short, long, int...search me.

I figured it was wrapping when I posted it, but I wanted to be sure. All that x1000 multiplying will be taken out...but I kinda liked it.

EDIT: and thanks Zip for that bitshifting tip. I forgot all about that, and I may look into it. I'm not sure if I'll use any more mathematical magnification of data. If that's what you call it.

Sorry for using everyone's time.

Hey, hey, let me defend my integrity a bit here. I'm not stupid, I'm just not professional.

When you say "good portion of the Verge community DOESN'T have a formal programming background"...I'm going to say, "No, really?"

A lot us of get into this stuff early...I think, and I've been interested in Verge since high school. Riding on nothing but some Atari Basic 800XL experience (thank you, grandfather), which was then revamped when I figured out what the heck a "function" was. I plan on raising my kids the same way. (Here's a Nintendo, Game Boy, Atari 800XL, SNES/Genesis, Crappy Pentium 90mhz, your first RPG maker, Intro to Verge, a Real Computer to aid you in all things technology-related, and from there you're on your own, son. Don't let me down.)

Professional? Heck no. I improvised, and I'm proud :) Which, is probably going to be the rule, because I don't think I'm going to pursue computing in college. I think.

And that is why internet tutorials will always be my friend. That ought to be a section of my site...or, this site. Just a whole LOAD of tutorials. For everything. In fact, can we submit links? I'd check right now, but as I post this my wireless is down because my family's on the phone (yes...when my family picks up the cordless phone, the laptop's wireless connection dies. I find it has something to do with the vector collision between the unit vector of the phone to its receiver and the computer to the wireless hub. Mainly because she's on the other side of the house, and yet despite being practically ten yards from the wireless hub (I've even failed to get a connection at 10 inches with phone on), I'm....well. I'm rambling a lot, aren't I?

Well, don't be too impressed. Right now I'm trying to implement bitshifting and I'm screwing everything up :)

Er, that's not the problem. I'm just screwing up all the calculations in general now, and I'll probably have to end up re-implementing all the matrix stuff. It isn't worth the time trying to fix it because I've got no clue what I'm doing wrong.

EDIT: Nevermind. Turns out I was fixing the bitshifting when I removed a crucial cos() function. Cos(z_angle)>>8 suddenly became (z_angle)>>8 and stuff started dying.