Cannot make script to rotate sun

Question

I tried to make a script to have the sun in my scene travel through the sky, and I the sun wouldn't move, nor will the light change. What am I doing wrong?

 using UnityEngine;
 using System.Collections;
 
 public class SunSpinner : MonoBehaviour {
     // How many second between day/night ticks (3600 per day-night cycle)
     [SerializeField] private float daySpeed = 0.05f;
     // Days that have passed
     [SerializeField] private float daysPassed = 0f;
     // Holds the sun's transform
     [SerializeField] private Transform sunTransform;
 
     // When was day/night last updated
     private float lastTimeTick = 0f;
     // Complete rotation of the sun
     private Quaternion solarRotation = new Quaternion(90f, 0f, 0f, 1f);
     
     // Update is called once per frame
     void Update () {
         if (Time.realtimeSinceStartup - lastTimeTick >= daySpeed) {
             // Rotates the sun by 0.01 degrees
             solarRotation.x = (solarRotation.y + 0.1f);
 
             //Sees if a day has passed
             if (solarRotation.x >= 360f) {
                 solarRotation.x = 0f;
                 daysPassed ++;
             }
             
             //Rotate the sun very slightly on the X axis
             solarRotation.z = solarRotation.x + 0.00001f;
 
             // Prepares for next rotation and updates the game object
             sunTransform.rotation = solarRotation;
             lastTimeTick = Time.realtimeSinceStartup;
 
         }
     }
 
     public void Reset () {
         lastTimeTick = Time.realtimeSinceStartup;
     }
 }

Answer 1

Best Answer

Answer by LazyElephant · Dec 16, 2015 at 02:03 AM

Long story short, changing the x, y, z, w variables in the quaternion doesn't do what I think you were expecting. Changing those variables directly generally isn't a good idea unless you really know the math behind the scenes, because it's not the same as simply adjusting the x/y/z rotations. You can make your script work by changing your solarRotation variable from a Quaternion to a Vector3 and by changing line 33 to sunTransform.rotation = Quaternion.Euler(solarRotation);

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14ercooper · Dec 16, 2015 at 03:29 AM 0

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The sun still stays just a touch above the horizon, and then doesn't move.

LazyElephant 14ercooper · Dec 16, 2015 at 03:33 AM 0

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For my test, I just placed it on a directional light to make sure that it was rotating and the lighting would change. The reason for your sun not moving is probably specific to your setup. How do you have your sun set up in your scene?

14ercooper · Dec 16, 2015 at 03:41 AM 0

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My sun is the one that comes defaulted to the scene, with only that script attached.

LazyElephant 14ercooper · Dec 16, 2015 at 03:57 AM 0

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oh, it's my fault. I forgot to mention that I also changed line 21 to solarRotation.x = (solarRotation.x + 0.1f);

In the script you have, you're setting it to solarRotation.y + 0.1f. But since solarRotation.y isn't changing anywhere in your script, you're just setting the solarRotation.x to the same value every time.

One other thing you'll see when it's running is that the rotation value for x will actually be counting down instead of up and it will automatically wrap around to 360 when it reaches 0. So you'll need to adjust your day tracking code.

14ercooper · Dec 16, 2015 at 03:55 AM 0

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Also, does not work with a fresh directional light

maccabbe · Dec 16, 2015 at 04:00 AM 0

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It sounds like your "sun" is just the directional light. Its position should not have any effect on your game.

However if you wanted it to see it "move" or "travel through the sky" then you have to change its position not its rotation. This can be done directly using transform.position or indirectly in a number of ways including transform.RotateAround

http://docs.unity3d.com/ScriptReference/Transform-position.html

http://docs.unity3d.com/ScriptReference/Transform.RotateAround.html

14ercooper · Dec 16, 2015 at 04:04 AM 0

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Thanks! That worked.

Answer 2

As @LazyElephant stated, the problem is misuse of Quaternions, but what may seem like the simplest solution does not actually function as easily as it could. Euler angles may seem correct at first, but the way Unity handles them comes second to directly-Quaternion-based functions.

One possible way of accounting for this is, rather than using the sun's position to determine the time, use the time to determine the sun's position. For instance:

 // C#
 
 [SerializeField] private float dayCycleTime = 180.0f; // 3600 * 0.05
 
 [SerializeField] private float rotationAngleOffset = -90; // Starting rotation from (0, 0, 0), where a time of "0" is midnight, offset rotation by 90 degrees
 
 [SerializeField] private Vector3 sunRotationAxis = Vector3.forward; // Rise in the east, set in the west
 
 private float sunSpeedScale; // 360 degree rotation occurs in "dayCycleTime" seconds.
 // This scale will accommodate this using the formula (360 / dayCycleTime)
 
 void Start()
 {
     // Correct for dayCycleTime <= 0
     if(dayCycleTime <= 0)
     {
         dayCycleTime = 0.0001f;
     }
     sunSpeedScale = 360.0f / dayCycleTime;
 }
 
 void Update()
 {
     // use of Time.realtimeSinceStartup may be replaced in order to choose when time starts, or to be able to pause time as desired
     sunTransform.rotation = Quaternion.AngleAxis((Time.realtimeSinceStartup * sunSpeedScale) + rotationAngleOffset, sunRotationAxis);
 }

This version should not find itself caught in the data-type conversion between euler angles and Quaternion rotations which prevent high values from being utilized.

Cannot make script to rotate sun

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