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How to create animations involved two actors?

Started by December 09, 2021 02:17 PM
4 comments, last by hplus0603 2 years, 10 months ago

Hello! I'm a software engineer (specialising in web development) looking to step into the world of game development and wanting to make a game as a hobby project. I've decided I want to make a simple pro wrestling game. If I can get two humanoid characters performing a couple of wrestling throws, then I'll be happy!

One topic I'm struggling to find resources on is the actual animation of moves. How would I go about creating an animation that involves two game actors? As one wrestling would need to throw another wrestler, but the wrestlers that are attacking and defending should be interchangeable.

As some background, I'd be using either Unity or Unreal Engine 4, and Blender for modelling and animation. And I would be doing keyframe animation as opposed to something costly and involved like motion capture.

That's pretty much the hardest kind of challenge regarding animation. What should help is using Inverse Kinematics and constraints. E.g. you could constrain the hands of character 1 to the belly of character 2. Then, if you lift up the second, the firsts hands should follow the belly and it looks like one lifting up the other. Beside this, physics simulation (ragdolls) can help with realisitc falls, for example.

Though, doing this manually and lacking former experience, results won't be anything like real life.

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I suppose that my question is this: How realistic do you want this to be?

If you don't mind a some stylisation, you can probably get quite far with simplified animations and a bit of interpolation to get the characters into their intended relative -positions and -orientations.

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The big question is how different the wrestlers are from each other. If they're all texture swaps of the same model, then you only need one set of animations. If they all have radically different body shapes, then each pairing of wrestlers needs a unique set of animations. You may be able to stretch a smaller number of animations by blending animations together - for example, throwing a medium opponent could be a blend of throwing a big opponent and throwing a little opponent, but only if the original animations are similar enough that blending them makes sense.

Either way, the process is pretty much the same: load both wrestlers into the same Blender project and start animating.

Typically, this is done by creating a shared reference point (say, a center point on the ground) and then animating both of them relative to that reference point. If you start this animation when the actors are not in the right relationship to each other, you have to first move them there – e g, one actor moving/running to the desired start point, or just snapping.

More advanced options would be to use IK to animate target positions for target bones hands, feet, head, etc) and then run some kind of physics/IK simulation to make the characters reach the appropriate positions, but without the torsos or limbs intersecting. Unreal Engine is adding some of these “physics based animation tweaks” to UE5 (they show some in their video footage) but it's not a general system yet. Nobody else has this solution as something you can buy/download, either, because it ends up being very hard to author and very game specific. With Unreal you get the source code, and can add the features you need, though.

But, if you're not a practiced 3D programmer / animator, this would be considered “very hard” – still fun, I'm sure, but could be the kind of thing that breaks you if you're not careful :-)

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