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IfThen Software LLC

Official IfThen Software LLC development journal.

Author: InvisibleLf

Newsletter #70 - Stalled Stacks

Posted by InvisibleLf Thursday November 18 2010 at 8:22PM
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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

Newsletter #69 - SAO Updates Soon

Posted by InvisibleLf Thursday November 11 2010 at 8:28PM
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News

Development on Stick Adventures Online will be starting very soon. Check the game's website to see our progress till then.


From the Programmer
Written by Invisible

I've spent the last 4-5 months studying physics. I'll need that knowledge for Merki, the SAO updates, and probably every other project we work on.

For anyone interested, these are some good resources for learning physics:
http://www.brightstorm.com/math - Introduction to calculus
http://ocw.mit.edu/courses/mathematics/ - Calculus, differential equations
http://www.physicsclassroom.com/Class/ - Beginner level physics
http://electron9.phys.utk.edu/phys135d/Modules.asp - College level physics. There are some typos though, so watch out for that.
http://chrishecker.com/Rigid_Body_Dynamics - Rigid body dynamics, specific to game programming.
http://gafferongames.com/game-physics/ - Solid groundwork for making a physics simulation.
http://www.cs.cmu.edu/~baraff/sigcourse/ - Particle systems and rigid body dynamics, specific to game programming.

So far, I have a working particle system and unconstrained rigid bodies. If you are interested in seeing the physics system in its current state, you can get it here.


Artist's Easel
Written by GreyKnight

iScribble Sketches #27

(Click to enlarge)



Community Spotlight
Written by jaythemage

In August, after Corvus stated that mods were dead because of the strict rules of using copyrighted material, Ace created and released a "Mod Scene Defibrillator" called SAO_DAT_EDIT. This program allows users to edit the DAT files of SAO to change image proportions which enables modders to edit the sizes of the sprites and have an even broader variety of ideas for mods. However, the program has not been used to create any mods by this time despite the major potential of the program.

The wait has been long, but fans of Stick Adventures Online are finally getting another major update. There have been several predictions of what exactly will be included in the update; however, the most common are that there will be at least one new map and that there will be several new enemies. Though there will be a price to pay for the update, many fans are willing to pay to play SAO's big update, even though they do not yet know how much it will cost.

Funny Quote of the Week
From the SAO moderator's channel

Background information: An SAO player had just been banned for swearing. pifreak (an SAO moderator) then said this in the moderating channel, regarding the recent ban.

pifreak: *tutorial* How not to respond to the queston: "Why did you avoid the filter?"
pifreak: "i dont know i'm kinda bored lol"