Euler Angles

Part of the Physics and Gameplay section of Coddy's Unity journey. Lesson 42 of 71.

transform.eulerAngles is an object's rotation as three angles in degrees, around x, y and z. Unity stores the rotation as a quaternion (the next lesson) and works the three angles out again each time you read them, always as values from 0 up to 360. Tilt a plank to -10 degrees around z and read it back:

transform.rotation = Quaternion.Euler(0, 0, -10);
Debug.Log(transform.eulerAngles.z);   // 350

You set -10, but the code reads 350, so if (transform.eulerAngles.z < -5) is never true. Reading back can change all three numbers: set (100, 0, 0) and you read (80, 180, 180), the same orientation written another way. Quaternion.Euler(x, y, z) goes the other direction and accepts any angle: -10, 350 and 710 build the same rotation. So keep the angle in a float of your own, change and limit it there, and set the whole rotation from it. This seesaw tilts with the arrows and stops at 20 degrees either way:

public float speed = 40f;
float tilt;

void Update()
{
    tilt += Input.GetAxisRaw("Horizontal") * speed * Time.deltaTime;
    tilt = Mathf.Clamp(tilt, -20f, 20f);
    transform.rotation = Quaternion.Euler(0, 0, tilt);
}

Do not change one part of the angles you read. transform.eulerAngles.x = 110; does not compile (CS1612, as with position.x), and copying eulerAngles, changing x and assigning the copy back starts from Unity's version of the angles. After setting (100, 0, 0), that copy is (80, 180, 180); add 10 to x and you get (90, 180, 180), which turns the object back to 90 instead of on to 110.

Challenge

Medium

Fix the camera's sweep: it turns back at 45 but not at -45, because eulerAngles.y reads -45 as 315.

Add a field float angle; and replace the two first lines of Update() with angle += direction * speed * Time.deltaTime;.
Keep the two if lines, then set the whole rotation: transform.rotation = Quaternion.Euler(tilt, angle, 0);.

Press Play: the camera sweeps from 45 to -45 and back, tilted down. Then Check.

Try it yourself

using UnityEngine;

public class Sweep : MonoBehaviour
{
    public float speed = 30f;
    public float limit = 45f;
    public float tilt = 20f;   // degrees down, around x
    float direction = 1f;

    void Update()
    {
        transform.Rotate(0, direction * speed * Time.deltaTime, 0, Space.World);
        float angle = transform.eulerAngles.y;
        if (angle > limit) direction = -1f;
        if (angle < -limit) direction = 1f;
    }
}

All lessons in Physics and Gameplay

1Rigidbody

Gravity and Mass Push with AddForce Jump with an Impulse FixedUpdate for Physics Velocity Kinematic Bodies Recap: Launch Pad

4Coroutines

Invoke InvokeRepeating, CancelInvoke Your First Coroutine Loops in Coroutines Stopping Coroutines Recap: Countdown

7Rotation

Euler AnglesQuaternions Face the Way You Move Turn Smoothly Recap: Turret

10Project: Arena Escape

Open After the Last Wave

Practice on your own: Unity playground