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Newsletter #70 - Stalled Stacks

Rigid body simulation trouble, sketches, new mods in the works.




News

There is no news to report in this issue.


From the Programmer
Written by Invisible

It turns out that my previous trouble with non-penetrating rigid body simulation was actually caused by an incorrectly calculated collision normal. On vertex-vertex collisions, the normal was chosen to be pointing in the direction of the center of the body to the point of collision. Handling vertex-vertex collisions as vertex-edge collisions solved the problem and the simulation no longer stalls as frequently when two bodies collide.

You might have noticed I said "as frequently". That is the problem I have been trying to tackle since Monday. The simulation will sometimes stall when two bodies collide, and it will definitely stall if I try to stack two or more bodies on top of each other (or push them into a wall, etc). I suspect this is at least partially because I am not applying resting contact forces.

I read through the "Resting Contact" section of David Baraff's "Rigid Body Simulation II - Nonpenetration Constaints" from "Physically Based Modeling". It was informative, but unfortunately not practical for me since it relies on having a quadratic program solver.

"Linear programming" and "quadratic programming" are new to me, and so I have spent the previous few days learning the basics. Hopefully this will be enough to get through the next article I am planning to read, also by David Baraff, titled "Fast Contact Force Computation for Nonpenetrating Rigid Bodies". From what I have read, the method described by it does not require solving an optimization problem, so it should be a lot easier to implement.


Artist's Easel
Written by GreyKnight

iScribble Sketches #28

(Click to enlarge)


(Click to enlarge)



Community Spotlight
Written by jaythemage

With anticipation about the SAO update on the rise, some members are taking the time to create some mods while the current version is still the only version of the game.


Funny Quote of the Week
From the online chat

Background information: "neko" is the Japanese word for "cat".

Jay: If a single humanoid alien attacked your hometown and was destroying everything it saw with super lazer beams from its eyes, and told you that you could take one thing out of your room to battle it, what would you take?
InvisibleMan: Err, the SNES I guess. It can't be used for anything else
Jay: I think I'd take one cat from each of my houses
Jay: Assuming I get one thing from each of my rooms
InvisibleMan: So you'd be kind of like a necromancer?
Jay: Heh, more like nekomancer

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