# bpj1138

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1. ## X-Purge 6

Unfortunately, I just tested the engine again and found it still "BLOWS UP". Stay tuned...
2. ## X-Purge 6

When such an error occurs, he X-Purge engine will print out an error message, like "tangent not unit"... which means, relative collision velocity was zero, therefore there was no tangent vector. It's always at the extremes where the system fails.
3. ## X-Purge 6

My thoughts? My thoughts are I'm not sure how to respond to this thread. Are you asking for specific feedback about a specific problem/question/potential solution? [/quote] I'm asking for other people's experiences solving the contact force problem. It seems to me when objects come to rest, which is obviously the solution, velocity goes to zero, therefore, you have to "catch" that condition in the code, which is obviously an invalid condition... velocity is zero, therefore time is zero, or objects are "at rest"...
4. ## X-Purge 6

Hello everybody, I've been working on my 3d verlet engine, and I thought I should share some insight about this before I upload the new version. First of all, if you haven't noticed, the previous versions of the engine would occasionally "BLOW UP" for no apparent reason. Well, that is what is being addressed in the current version. Things that I have found out in the process are: 1) don't assume the problem is the friction calculation (see below) 2) if the intersection code is faulty, all bets are off, therefore friction calculation can fail as the result 3) most of the errors are caused when velocity vanishes, this means there is no tangent vector! 4) when all else fails, just abort the operation... the next interation will handle it Your thoughts?
5. ## Resolve resting contacts

This is why this problem is so difficult. As time goes to infinity, the jitter goes to zero. Zero velocity is a bad situation, because you have no normal or tanget vector, and so you cannot calculate friction to stop the motion.
6. ## The Laws Of Physics, Where Did They Come From?

The answer is that 2 + 2 can equal 5, if God wanted it to be that way. People talk about fine funing the universe, but actually, you can make anything work out if you want to. 10 + 5 could equal Pi... l8r..
7. ## Reliving your own life?

Phantom: Thanks for remembering.. I know you're watching me.. Yes, 2 posts... Hodgman: I'm sorry.. I should have replied to you earlier. You're absolutely correct. Time does NOT exist. It is not a substance that can be "diluted" as in Einstein's theory.. The way I always explain it, is mathematicly, which is that time is a dependent variable. Dependent on the 3 spacial dimensions. We all know, distance = velocity * time, so time = distance / velocity. If there was no movement, time would "stand still". Now, some ppl will argue that time dilation is a proven phenomenon. I agree that certain particles do experience a delayed decay, BUT, the reason for this can be explained in OTHER ways than time dilation!... Namely, if a particle is traverling faster than the surrounding SPACE, it is experiencing additional PRESSURE of the EM field. That is what keeps it GLUED longer than the other particles! So, just because you observe something to be true, there could be MANY _different_ explanations for the phenomenon.. BUT, of course, I'm telling you things you already know. In any case, thank you for your reply... I REALLY appreciate it..
8. ## Reliving your own life?

All right, calm down everybody. First of all, I'm talking about La Sage, not Lebinz, so go look up "push gravity" or "shadow mechanics". Lebinz supposedly invented calculus before Newton. Then again, who knows who stole what idea from who (yes, I deliberately butcher the English language). Phantom, stop stalking me! Ok, I leave you with this: I just went to the DMV to "exchange" my driver's licence, because I moved to Ohio from Florida. I still don't understand why, I live in the UNITED states. Anyway, Ohio requires such people to take the written exam before they issue you an Ohio license. So here we go, let's take the test. They direct me to a computer station, which they told me could read the questions for me. I told them, "thanks but no thanks, I'll read them myself".. First question... what is 2 + 2? I'm not shitting you! I suppose it's a "sanity check", but given our current discussion in time, how is that a coincidence? I wanted to laugh, but I figured if I did the cops would probably handcuff me. This makes me believe in my original premise, which is that my life is a world onto itself, but truthfully, I don't really believe that. I'm not that smart. I couldn't have invented all this! And I learned everything I know from other people. God bless you all..
9. ## Reliving your own life?

I tend not to believe professional theories, because they are also part of a dogma which much like the other dogma is self reinforcing. Notice I didn't say that it only reinforced material beliefs, because scientists routinely break that rule. For example, extra dimensions of string theory, Einsteins curved space, dark matter, and so on. In the case of deja vu, it's simply a foregone conclusion based on the orignal scientific dogma that everything has to be resolved through partical interaction, nevermind what particals are or who put them there. So, when it's convenient, they use the material argument, but then promptly invent exotic materials or dimensions when their equations don't work out or disagree with observation. I agree, and I believe there is a practial theory that describes the material universe very eloquently, and this theory has been buried a long time ago. You see, when Newton came up with his gravity "theory", many people were asking "what is the mechanism of gravity", because Newton's "theory" was only a description of what happens, not how it happens. Well, not many people know that Newton had an adversary who gave exactly such a mechanism. Unfortunately, since this adversary was an unknown and Newton was the mathematics chair at Oxford, politics not science now dictate who's right and who's wrong. This was the greatest blunder in human history. I'm guessing it will take another thousand years for us to correct this, and the only way to do so is to go around the mainstream scientific community which now just like then is based on politics, popularity, money, and hurd mentality more than anything else. Luckily, power has been returned to the people through the Internet, however, it takes a lot of effort to undo the damage that the dogma has caused. The underground is also filled with crackpots, just like the mainstream. So, good luck to anyone trying to make sense of "scientific" theories. What if I'm correct and you either go on to the next life or relive your life again? In other words there is no heaven or time in between when you get the answers to such questions. In that case you can only figure it out within your lifetime. Then again, if you're not meant to do it, you never will.
10. ## Reliving your own life?

It occurred to me the other day that maybe the reincarnation theory is wrong, and what actually happens is you relive the same life over and over again? This would explain deja vu. The long version is this. I was also thinking of how people can't imagine the universe having always been and always will be, but curiously, nobody would argue that numbers have always existed? Maybe God doesn't exist but numbers do. There is even circumstantial evidence for this, which is the fact that even God cannot make 2 + 2 == 5, which negates one of the supposed powers that God is supposed to posses, namely, omnipotence. In theory, if you have a sufficiently long number, it could define your whole life. You and everything you experience. Why not? Unlike the "real" universe, there are no limits to the capacity of numbers. You can have any combination at all, defining every atom in your body and all the stuff you see in front of you. Furthermore, conciousness works on the anthropic principle, that is, there are infinite random combinations, and most of them end up not creating conciousness, yet, some will necessarily hit on the right combination to make conciousness, and therefore, if you're concious, you must be one of the right combinations. The end justifies the means. I'm actually a disbeliever myself. One of the reasons is that this would probably lead into the horrible thought that you're alone in your own creation. After all, how would this explain other entities interacting with you? One possibility is that numbers that are relatively close define the same type of entity. So for example, a large part of a number would define your home planet and then the minor part would define you and your friends. But still, it seems all these number are independent of each other, so you could have your own definition of people within your life that had nothing to do with someone else's definition. Does any of this make sense? I hope not. I actually like God, and would hate to lose a friend like that.
11. ## Linus Torvalds and his smackdown speech

I have to say I agree with him. Remember Java came about in order to purge some of the useless and/or confusing features of C++. Code readability is important, and if you give people enough rope, they'll hang themselves. However, given how Java never really caught on because it turned out to be slow, and x86 remained the processor of choice instead of Java processors, C++ was resurrected in order to rectify this situation. The truth is, the computer world can never make up its mind, much like the US voters. So, the answer is, use C++, but only the base features. Problem solved (sort of).
12. ## Handling object collisions

I'm convinced. BTW, have you ever played Pulsoids? http://www.simtel.net/product/view/id/138992 One of these days I'll upload the new version.
13. ## Handling object collisions

Right, I use spatial hashing for object<->world collisions as well. You can also use it for storing the visibility set. I even went as far as hashing the angle of view. Once that's done you just divide the object's position by the cell size and convert that to integers which gives you indexes into the collision/visibility arrays. I can't think of a quicker way to get at the relevant data.
14. ## Contact force situation

I suppose you could integrate the equations symbolicly inside the time step. In classic RBD, you almost have to do this in order to conserve angular momentum properly, otherwise the system will leak energy. You can see this clearly when an object is nutating. A first order integrator will not work, or only work for a few seconds. As far as stability, I haven't seen an LCP engine, so I can't say one way or another. I do know that adhoc methods have problems, because they have no concept that the solution depends on the entire system, rather work on pairs of objects separately from all the others. This leads to impulses applied in opposite directions that grow in strength in order to componsate for the impulses working in the opposite directions. To use an analogy, think of people talking at a party, and having to talk louder and louder in order to be heard, meanwhile all the other people also start talking louder and louder so they can be heard, and so forth.
15. ## More question on Verlet

[attachment=10606:VerletWellBin.zip] This should help visualize the situation. Look at the vertexes of the boxes. Red light means dynamic, Green means static, and Blue means "dampening" (something I added). Hope that helps. BTW, I'm told you can disassemble this code.. Good luck.. PS: when the system seattles down, you'll see the lights blinking rapidly. That is the shock wave traveling through the system. --Bart