Quaternion.Slerp timescale behavior

Questions & Answers
1

I’ve got a coroutine that I’m calling to rotate and object so that it faces another direction using Quaternion.Slerp. It doesn’t seem to be rotating correctly however:

public IEnumerator QuatRotate(float _rotateSpeed)
	{
		float rate = 1.0F / _rotateSpeed;
		float timeScale = 0.0F;
		while(timeScale < 1.0F)
		{
			timeScale += Time.deltaTime * rate;
	    	transform.rotation = Quaternion.Slerp(transform.rotation, Quaternion.Euler(0F,180F,0F), timeScale);
			print(timeScale);
			yield return null;
		}
	}

I’m printing out timeScale to the console and I can see that it’s incrementing upwards to a value of 1.0F as it should, but the slerp function seems to be ignoring this and rotating at a different rate, even though I set timeScale as its t parameter. I get how Unity’s Lerp functions work, using 0…1 as relative distance between the first two parameters, but it doesn’t make sense when I see timeScale incrementing linearly while the object rotates either too fast or too slow.

3

Below is your code with a few tweaks. From your naming I assumed you would want _rotateSpeed to represent the number of times the object would make the 180 degree rotation in a second (though it only makes one rotation). So a value of 2 will rotate the 180 degrees in 1/2 second. A value of 0.1 will take 10 seconds to rotate. Using the current rotation rather than saving the start rotation was the biggest issue with the timing.

public IEnumerator QuatRotate(float _rotateSpeed)
{
   float rate = 1.0F / _rotateSpeed;
   float timeScale = 0.0F;
   Quaternion q = transform.rotation;
		
   while(timeScale < rate)
   {
     timeScale += Time.deltaTime;
       transform.rotation = Quaternion.Slerp(q, Quaternion.Euler(0F,180F,0F), timeScale/rate);
     //print(timeScale);
     yield return new WaitForEndOfFrame();
   }
}
2

This is how I rotated my camera to rotate to a specified location. You could use it or modify it to your needs. It is in boo.

def rotateToObject ( target as Transform, time as single ) as IEnumerator:
		initialRotation as Quaternion = transform.rotation
		targetRotation  as Quaternion = Quaternion.LookRotation(target.position - transform.position)
		rate            as single  = 1.0/time	
		delta           as single  = 0.0
		
		while delta < 1.0:
			delta += rate * Time.deltaTime
			transform.rotation = Quaternion.Slerp(initialRotation, targetRotation, delta)
			yield

Using ‘as’ is Boo’s way to instantiating type. Also single is float in C# and JS