Engine for 2D Top-Down Physics-Based Skeletal Animation

Question

I just watched at the Sui Generis video, and was completely amazed. Specifically, the part where the big troll thing is beating up the player with his flail.

This got me really excited, and I would like to try implementing something like this in a 2D Top-Down format. Something like this.

That atloria example seems simple enough, but it's not exactly what I'm looking to make. I think atloria is using predefined animations, where as I would like to make something more physics-based like the Sui Generis engine does.

So, I'm wondering what physics engines might work for something like this, and if I'd need to implement my own skeletal system, or if I could just use "joints" and such from the engine. The only experience I have in terms of physics engines is Box2D, which I've heard shouldn't be used for top-down settings, and I can think of a few reasons it wouldn't work out well. One of those reasons being gravity. In box 2D, gravity pulls towards a side of the screen (usually the bottom.) I wouldn't want my player's forearms constantly being pulled to one side. :)

Also should mention that the programming language doesn't matter all that much to me. I'm currently playing with HTML5 stuff, though. :)

Thanks in advance!

Answer 1

Any physics engine can do (at least) half the work for you. The effect you're seeing is achieved by blending ragdoll physics with explicit animations. You can do this by having animations apply forces to bones and letting physics do the work for you. I haven't implemented this myself so I'm not 100% sure on the technique, but there's some articles out there on the Web on it.

Wolfire's blog used to have some good articles on it, but I can't for the life of me find them right now. BTR Studios has a nice overview of the technique. There's a great set of slides on Just Cause 2's ragdoll animation blending. Google "ragdoll animation blending" and you can find more.