Turn Smoothly

Part of the Physics and Gameplay section of Coddy's Unity journey. Lesson 43 of 63.

Setting transform.rotation straight to a new rotation turns an object in a single frame. Quaternion.RotateTowards(current, goal, maxDegrees) returns current turned toward goal by at most maxDegrees, and never past the goal. With turnSpeed * Time.deltaTime as the step, the object turns at a steady rate and stops exactly on its goal, as MoveTowards does for positions. This sunflower follows the sun at 30 degrees per second:

public Transform sun;
public float turnSpeed = 30f;

void Update()
{
    Quaternion goal = Quaternion.LookRotation(sun.position - transform.position);
    transform.rotation = Quaternion.RotateTowards(transform.rotation, goal, turnSpeed * Time.deltaTime);
}

A sun 90 degrees away takes the sunflower 3 seconds, 30 degrees in each. It turns the short way round, and the goal is worked out again on every frame, so a moving sun is followed.

Quaternion.Slerp(a, b, t) is the rotation a fraction t of the way from a to b, as Vector3.Lerp is for points. Written as Slerp(transform.rotation, goal, 5f * Time.deltaTime) in Update(), it turns a share of the remaining angle on each frame: quick at first, slower and slower near the goal, never at a set speed and never quite arriving. That ease suits a camera or a head turning. When the turn rate is a rule of the game, such as a cannon that turns 60 degrees a second, use RotateTowards.

Challenge

Medium

The owl turns to look where you point it. Each arrow gives it a new direction to face: up +z, right +x, down -z, left -x. On a press it starts turning toward that direction at turnSpeed (180) degrees per second, at a steady rate, and it finishes the turn even after the key is let go, stopping exactly on the new direction.

Press Play, press the arrows, then Check.

Try it yourself

using UnityEngine;

public class Owl : MonoBehaviour
{
    public float turnSpeed = 180f;

    void Update()
    {
        // Up, right, down, left: turn to face +z, +x, -z, -x at turnSpeed degrees per second.
    }
}