Quaternion vs Euler in game engines

PolyHertz

I was wondering if performance wise there was any reason to use Quaternion/Euler over the other? Are there any known major issues with using either of them in Unity/UE4 to be aware of?

fmnoor

At the end of the day, all rotations are handled as a quaternion (I'm pretty sure about this across all game engines - I could be wrong about UE4 though but I'm going to guess it does quaternion). They are more efficient. Here's a good breakdown of both : https://knowledge.autodesk.com/support/maya/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU/Maya/files/Animation-Basics-Animated-rotation-in-Maya-htm.html

Farfarer

Quaternions don't tend to suffer from gimbal lock and such, too (and they're faster to compute and stack I believe).

kio

i think its more about editing than performance - quaternion as curves just  ... well... don't really work. 

PolyHertz

Another related question; is it ok to mix both Euler and Quanternion in a rig? Like say having the root as a Quanternion so that a character can act like an acrobat doing rolls/flips/etc. , while using Euler for the rest?

JedTheKrampus

You can probably use Euler angles for anything that only needs to rotate around one or two axes, like an elbow. For stuff that requires more degrees of freedom like an arm socket it's better to use quats. In the end (in the engine) it's all quats anyway most of the time.

echofourpapa

In Unity I'm not aware of a way to rig and animate with Quaternions, only Euler angles.  You do have access in code to the Quaternions, and it has lot of helper functions to translate between Euler and Quaternions.  The Unity docs on it are here.  

PolyHertz

Bumping since still don't have an answer to my second question posted above (is it ok to mix TCB and Euler controllers in a single rig)

fmnoor

Yes it should be fine. I suspect most animators would prefer Euler for most things though. 

http://polycount.com/discussion/comment/1356904/#Comment_1356904

Farfarer

Yeah, shouldn't be a problem.

They may get rigged as Euler or TCB... but they're going to get exported as keyframes in the same specification regardless of how you actually get the rig to rotate.