Search found 26 matches

by ewjordan
Fri Oct 31, 2008 10:42 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: ApplyForce() adds excess energy
Replies: 3
Views: 1634

Re: ApplyForce() adds excess energy

While that whole thing is probably worth reading anyways, the quick answer is that there's no requirement that the same force over the same time adds the same amount of energy; change in energy is the integral of the force over distance (dotted appropriately, of course), not time, so the answer is t...
by ewjordan
Tue May 20, 2008 10:36 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: CA and numerical integration and root finding
Replies: 18
Views: 4923

Re: CA and numerical integration and root finding

However, I put a ball inside that box, eventually the ball will tunnel outside of the box (yet remain inside the static region). I believe this shortcoming to be related to linearization of rotational motion. For example, the velocity of a pendulum is tangent, yet it moves inward. There could also ...
by ewjordan
Mon May 19, 2008 11:56 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: CA and numerical integration and root finding
Replies: 18
Views: 4923

Re: CA and numerical integration and root finding

Instead of calculating progressive conservative advancement steps and integrating the entire simulation, every body computes it's exact time of collision whenever it doesn't know its next time of collision. When the time of collision arrives, we solve the resulting island (that's the proper term, r...
by ewjordan
Wed Feb 13, 2008 9:06 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Collision normal perturbation
Replies: 2
Views: 2275

Re: Collision normal perturbation

This could be interesting if it works, particularly when applied in conjunction with visual bump or parallax mapping. However, there are pitfalls. First, make sure your normal vectors aren't causing collision resolutions to pump energy into the system - your normal vector field should be curl free, ...
by ewjordan
Sun Jan 06, 2008 11:25 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Newton's cradle
Replies: 8
Views: 9352

Re: Newton's cradle

Jan - I saw the videos (very nice work, btw!) and took a look through your paper, and I had a couple questions. Based on a quick reading, it seems that one distinction between your method and SI (at least as far as solving Newton's cradle goes) is that in SI one iterates over the contacts several ti...
by ewjordan
Thu Dec 13, 2007 5:35 am
Forum: General Bullet Physics Support and Feedback
Topic: Java Bullet
Replies: 3
Views: 1537

Re: Java Bullet

Please keep us informed if you're going to do this, I'm very interested in seeing this happen. If I have some time, I'd be willing to help, as I'm very much in a porting mood from working on a Box2d Java port (http://www.box2d.org). One suggestion, it might be a good idea to start from the XNA port ...
by ewjordan
Sat Oct 20, 2007 5:04 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Rope Physics in 2D
Replies: 3
Views: 7788

Re: Rope Physics in 2D

Well, good luck with it - if you need any help, let me know, I have used this method in games before: http://www.ewjordan.com/rgbDemo/ has a Java demo (applet) of a game I did this in, which is still unfinished. If you're on a 64 bit machine it might not run, it uses JOGL and I don't think I have th...
by ewjordan
Thu Oct 18, 2007 5:45 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Newton's cradle
Replies: 8
Views: 9352

Re: Newton's cradle

[Sorry, this is really long: long story short, don't hit your head against this stuff too much, there's no perfect solution] If you have something that works perfectly for Newton's cradle, it will give a nonsense result for an impulse applied to a "frame" of mass 1 exactly enclosing a row of several...
by ewjordan
Thu Oct 18, 2007 5:08 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Rope Physics in 2D
Replies: 3
Views: 7788

Re: Rope Physics in 2D

If all you need is rope stuff (and you don't need a full rigid body simulator), Verlet integration plus distance constraints by position projection is the simplest approach, and it's pretty fast. For each particle you store the current position and the last position, and time stepping is done as fol...
by ewjordan
Wed Oct 03, 2007 6:28 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Collision detection for mobile physics engine
Replies: 6
Views: 3368

Re: Collision detection for mobile physics engine

Figured I'd chime in here: I'm one of the people working on a port of Box2D to Java. Unfortunately at the moment we're not shooting for mobile Java yet, because a) we're still not sure how well things will run on regular old Java, and b) to use on mobile requires that all the math be converted to fi...
by ewjordan
Wed Oct 03, 2007 1:18 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Rigid Body Techniques
Replies: 7
Views: 5324

Re: Rigid Body Techniques

Practically speaking, Verlet-based simulation is easy to understand, which makes it initially attractive, and there is something nice about having velocity-free representations (if you've ever done PDE simulations, wave equations or something like that, you'll know how much easier these can be to wo...
by ewjordan
Sat Sep 29, 2007 10:56 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: 2d physics shape optimization
Replies: 2
Views: 1809

Re: 2d physics shape optimization

Probably not, is my opinion (others here definitely know more than I do, though). As far as I know, SAT is pretty much it for polygons, including triangles - you can't get much simpler than testing which side of a line something is on and by how much. The only caveat would be that you might be able ...
by ewjordan
Wed Sep 19, 2007 11:48 pm
Forum: General Bullet Physics Support and Feedback
Topic: Java physics engines?
Replies: 7
Views: 5181

Re: Java physics engines?

Alright, if I have the time I might see what I can accomplish here, probably with floating point at first - a Java port might be tricky to get running very fast, I'll have to take a look through and see whether there are things that could easily be changed to fix this (in particular object creation ...
by ewjordan
Tue Sep 11, 2007 11:07 pm
Forum: General Bullet Physics Support and Feedback
Topic: Java physics engines?
Replies: 7
Views: 5181

Re:

It seems to me that if you need to use physics within a Java program, you should be looking for a C/C++-based physics engine - and adding Java bindings to it so you can use it within Java code. That's not at all unreasonable since it keeps the heavy math in the C++ code and leaves you to do the hig...
by ewjordan
Wed Aug 29, 2007 1:07 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: [solved] avoiding jitter with verlet rigid bodies
Replies: 5
Views: 4337

What Dirk means by allow for some slop is that when you're fixing up the penetration, don't do a 100% projection; rather, figure out the correct place to project to, and project (say) 90% of the way there, or something like that. But I've got to say, that "dancing" looks a little more severe than I'...