How to do Cutting Animations and States?

SuperSparkplug

Hi there,

For a while I've been interested in how games like Fruit Ninja and Metal Gear Rising Revengence performed the act of cutting things in half, showing the inner part of the 3D model and spliting it into two or more meshes. I've tried looking it up and haven't exactly found much in the way of how to do it either in Maya or programatically in a game engine (eg Unity).



Coincidentally, the manager of my workplace is interested in exploring how to do this and tasked me today with figuring out how to do that. I've looked up and have read a few things on how it might be done in general and certain interesting details (via Platinum Games' Blog and a few other sources), but I still can't find anything on how to do it or at least in a manageable way.

Can anyone describe to me how or where exactly I can learn how to animate or program the cutting of 3D meshes that splits the mesh and exposes inner geometry which normally doesn't exist?

GlowingPotato

If i would guess... Real time tessellation and decal projection ?

I'am note sure...

SuperSparkplug

Even terms like that would be nice. I'm kind of in the dark about key words to search for.

Eric Chadwick

Games like Fruit Ninja just swap the models when you cut them. So the game shows you a "whole fruit" model, then when your cursor swipes across the physics mesh of the fruit (an invisible simple sphere shape), the whole model is made invisible and the pre-cut fruit model is made visible. It is given some physics forces to push the pieces apart, plus the game spawns a pre-made particle animation for the wet bits. The fruit always cuts evenly across the middle, because it's pre-cut!

For games like Metal Gear they use a variety of approaches. SimonT has some good links and pics here:
http://simonschreibt.de/gat/metal-gear-rising-slicing/

Unreal Engine has dynamic destruction using APEX, but it's not as granular as MGR's slicing:
http://udn.epicgames.com/Three/APEXDestruction.html
https://docs.unrealengine.com/latest/INT/Resources/ContentExamples/Destructables/index.html
https://docs.unrealengine.com/latest/INT/Engine/Physics/Destructibles/DestructibleProperties/index.html

Search for "fracture" "dynamic destruction" "constructive solid geometry" or "csg" etc.