Falling simulation

News & General Discussion
1

Not really sure where this topic would go so I am placing it here…

I was curious as to how to do a simulation of a person falling. Say you were to make a sky-diving game where most of the game is spent looking at someone falling, how would you recommend doing the simulation of the wind?

The two options I can think of is to make the animations static (I.e. You manually animate each piece of clothing and hair section that you want movable inside your 3D app and have the same animation play over and over) or dynamically by splitting your character into various polys like the trouser ends being a number of polys parented to each other and giving each one a rigid body and allowing physics to do the rest…(but how do you make one end parented to the one piece of the leg and the other end parented to the other side of the leg? Parenting the same object directly underneath two objects at once is impossible so this won’t work also) For the hair this would be fine, but what about the clothing?

I am eager to hear what kind of ideas you guys n gals have…

2

Hmmm… interesting challenge. I wonder if there might be something you could do with particles that would give you the illusion that fabric or hair was “flapping” in a breeze?

3

The closest thing to a solution that I was able to think of would be a hexagonally placed series of planes, each with a ridigbody and then attached to each other with a joint. Perhaps the joint could try to make it retain the original shape while the force of the “wind” would make it fold in around itself.

The main problem here, I would think, is creating realistic wind… I was hoping that by giving everything gravity and just pushing the character off the plane, the physics engine would do the rest, but I would assume it works only with collisions and gravity and doesn’t really take into consideration wind resistance in any way, shape or form apart from angular drag…

I suppose the simplest way to do this would be to place an ‘emitter’ of sorts at various places and making it do random raycasts around, say, the leg for instance, and only apply a wind-alike-push to each object it finds. Thus, the sides of the trousers would be “blown” away from the leg in opposing directions while the top is left unaffected by anything apart from angular drag. Thus just sit back and see how the various components make each other behave…

That was the idea anyways. To implement this would require a lot of work and I am still not sure how effective a solution if would be. Spending a couple of weeks tuning this only to find out it is a useless endeavor would be a bit of a blow…

Also, this idea is for an iPhone game I am planning so adding 250 ridigbodies with colliders and adding forces to each every frame combined with a 100 or so hinges… not really sure if the iPhone can handle such an incredible workload. Perhaps I should do that for a standalone release and focus on Maya-modeling my animations for the iPhone…

This was the purpose of the question. So to clarify it a tad further:
What ideas do you guys have for realistic cloth deformation on the iPhone or is Maya my only option?

I was interested in the particle option but I am not too clued up on particles, yet. I was thinking that would be a simple way of making random wind trails emminate next to the body parts, but since the trails will appear to be standing still when they appear, I figure UV animation of an image with alpha on a 2 poly plane would do just as well.

Have you got an idea of how to implement that idea of yours with particles?

4

Well the idea I had for using particles was basically to cause some sort of “animated movement blur” along the clothes. I don’t have time to build a sample and it would probably take a lot of experimenting to get it looking right.

Another idea would be to make the clothes a separate object from the body and use bones, rigidbodies, joints and physics to bend the clothes in the directions you want, ie. imagine a complex ragdoll sort of thing.

And a third idea might be to come up with a script that takes vertices and animates them with code to simulate the flapping.

Probably the easiest would be your initial idea and create the clothes flapping animations in your 3D app, but you’d have to create animations for various “wind” directions.

I seem to remember someone did a demo of a cape flapping in the wind, you might want to look for that demo. And lastly, if you really want to get into some heavy code, did you see the fabric softbody simulations in the Wiki? Not something I’d recommend for this particular application, but might be worth looking at.

Hope this helps…

5

As far as I know Unity doesn’t support vertex animation from Maya, does it? Only bone animation…

But that brings up an interesting point… Unity allow for one to manipulate bones via script… So building a series of bones for various parts of the clothing and animating it via bone manipulation… that could be an option… That offers a number of possibilities… Stretchiness and transform in one… That could be something to pay around with… Nice call…

Does anyone know how much of an overhead bones are? For instance, how much longer would it take Unity to render a character that has 8 bones vs a character that has 20… in keeping with that question, if I have bones for my body and then a number of bones for the clothing… how many bones can a character have before it becomes too many for the iphone to handle ?