Unity Quaternion Problem (Should be A Bug?)

Questions & Answers
1

Hi, i recently has a big problem. i searching from any forums and QA but didn’t find any luck.

so my problem is i want to move (and rotate) object by adding value on every Update() call, this is similar like to call Vector3.Lerp() and Quaternion.Lerp(). And this is my code :

void Update(){
if (doTim > 0 && Time.deltaTime > 0) {
	doTim -= Time.deltaTime;
	if (doTim != 0) {
	if (doPos)
		Behaviors [behaviorCycle].objTarget.localPosition += doPosTo / (doTimTotal / Time.deltaTime);
	if (doRot)
		Behaviors [behaviorCycle].objTarget.localRotation *= Quaternion.Euler (doRotTo / (doTimTotal / Time.deltaTime));
	if (doTim < 0) {
		if (doPos)
			Behaviors [behaviorCycle].objTarget.localPosition += doTim * (doPosTo / doTimTotal);
		if (doRot)
			Behaviors [behaviorCycle].objTarget.localRotation *= Quaternion.Euler (doTim * doRotTo / doTimTotal);
				}
			}
		}
}

the localPosition changes on this Update call are WORKED correctly, but for the localRotation, it rotation will ended with very strange value.

if I rotate it by only one Axis (say, from (0,0,0) to (0,90,0)) it will rotating correctly, but if I rotate it using two or more Axis (say, from (0,0,0) to (90,90,0)) it will returning very strange value.

so, What should I do? is there something I missed? I have trying to using Transform.Rotate() but it did the same things.

PS : I won’t use Lerp() function because the object are controlled by more than one script in my game.

2

The problem is that you are doing interpolation with quaternions, but calculate the delta for your rotation from euler angles. If you were interpolating over euler angles (as a vector), the result would be different than quaternion slerp.

If you want to inrerpolate rotation smoothly towards some target, i suggest you:

  • Calculate angle between current and destination target rotation, i think it’s angDist = Quaternion.Angle or something like that. The result is float
  • Calculate how much you want to rotate in this frame: angDiff = rotSpeed * deltaTime
  • Calculate the ratio of the total angle vs what you want to move, and feed that to slerp (not lerp, never lerp for quaternions that represent rotations). That would be: ** ratio = angDiff / angDist **
  • Last, you can do the Slerp correctly (as it’s meant to be, i never understand people who use deltaTime as lerp/slerp factor!!): newRotation = Quaternion.Slerp(oldRotation, targetRotation, ratio )