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Question Velocity number is not round when I put it in Fixedupdate.

Discussion in 'Scripting' started by Kokomeant, Dec 23, 2022.

  1. Kokomeant

    Kokomeant

    Joined:
    Dec 23, 2022
    Posts:
    13
    Hello, I'm unity beginner.
    I'm trying to create simple character movement with Rigitbody velocity, And now when i put the velocity code in the FixedUpdate the velocity number decreased to 2.292152 (my speed is: 3), But when i put the code in Update it works perfectly and stayed on 3 without any change, Now I'm asking it because i understood that a Rigitbody proprties should be in FixedUpdate and when you set the velocity and don't add velocity it shouldn't be multiplied with Time.DeltaTime.
    Here is my script:

    Code (CSharp):
    1. public class PlayerMovement : MonoBehaviour
    2. {
    3.     [SerializeField] float ForceSpeed;
    4.     [SerializeField] float jumpPower;
    5.  
    6.     Rigidbody2D Rb2D;
    7.  
    8.     private void Awake()
    9.     {
    10.         Rb2D = GetComponent<Rigidbody2D>();
    11.     }
    12.  
    13.     void Start()
    14.     {
    15.         ForceSpeed = 3f;
    16.         jumpPower = 6f;
    17.     }
    18.  
    19.     string keyDown;
    20.     void KeyIdentificator()
    21.     {
    22.      
    23.         if (Input.GetKey(KeyCode.D) && !Input.GetKey(KeyCode.A))
    24.         {
    25.             keyDown = "D";
    26.             Debug.Log(keyDown);
    27.         }
    28.         else if (!Input.GetKey(KeyCode.D) && Input.GetKey(KeyCode.A))
    29.         {
    30.             keyDown = "A";
    31.             Debug.Log(keyDown);
    32.         }
    33.         else if (Input.GetKey(KeyCode.D) && Input.GetKey(KeyCode.A))
    34.         {
    35.             keyDown = "Both";
    36.             Debug.Log(keyDown);
    37.         }
    38.         else
    39.         {
    40.             keyDown = "";
    41.             Debug.Log(keyDown);
    42.         }
    43.     }
    44.  
    45.     void CharacterMovement()
    46.     {
    47.         if(keyDown == "D")
    48.         {
    49.             Rb2D.velocity = new Vector2(ForceSpeed, Rb2D.velocity.y);
    50.         }
    51.         else if(keyDown == "A")
    52.         {
    53.             Rb2D.velocity = new Vector2(-ForceSpeed, Rb2D.velocity.y);
    54.         }
    55.         else if(keyDown == "Both")
    56.         {
    57.             Rb2D.velocity = new Vector2(0f, Rb2D.velocity.y);
    58.         }
    59.         else
    60.         {
    61.             Rb2D.velocity = new Vector2(0f, Rb2D.velocity.y);
    62.         }
    63.     }
    64.  
    65.     public int fps = 9999;
    66.  
    67.     private void Update()
    68.     {
    69.         Application.targetFrameRate = fps;
    70.         KeyIdentificator();
    71.        // CharacterMovement();
    72.         Debug.Log(Rb2D.velocity.x);
    73.     }
    74.  
    75.     private void FixedUpdate()
    76.     {
    77.         CharacterMovement();
    78.     }
    79. }
    80.  
    Sorry for my english, And Thanks in advance :)
     
    Kokomeant, Dec 23, 2022
    #1

  2. MelvMay

    MelvMay

    Unity Technologies

    Joined:
    May 24, 2013
    Posts:
    10,620
    You can only read input per-frame. You cannot/should not do it during the FixedUpdate.

    That's not true or is a bad version of the truth. You can set velocity whenever you like. The simulation will run by default during the FixedUpdate (although you can change that).
     
    MelvMay, Dec 24, 2022
    #2
    Kokomeant likes this.

  3. Kokomeant

    Kokomeant

    Joined:
    Dec 23, 2022
    Posts:
    13
    First of all thank you for the response.
    I think I'm a little lost, So I can set the velocity in Update because I'm setting the velocity right? But if I add velocity it should be in the FixedUpdate right?
     
    Kokomeant, Dec 24, 2022
    #3

  4. MelvMay

    MelvMay

    Unity Technologies

    Joined:
    May 24, 2013
    Posts:
    10,620
    Update vs FixedUpdate is nothing specifically to do with velocity or physics. Update runs per-frame which can/is variable. FixedUpdate, as its name implies, runs at a fixed interval.

    If you have any value and you add 1 to it during Update, it'll get 1 bigger every frame. If your frame-rate goes up, it'll go up faster and likewise slower if the frame-rate goes down. If you do that during the FixedUpdate then it's frame-rate independent and will always go up by the same rate which is 50Hz by default (can be changed).

    If you apply that to velocity then you'll get a differing change in velocity during update and a constant one if in FixedUpdate.

    As I say, it's nothing to do with physics and everything to do with timing.

    You can, of course, change velocity per-frame and scale that change by the elapsed time to make it change/sec.
     
    MelvMay, Dec 24, 2022
    #4
    Kokomeant likes this.

  5. Kokomeant

    Kokomeant

    Joined:
    Dec 23, 2022
    Posts:
    13
    I got it, Thank you very much! :)
     
    Kokomeant, Dec 24, 2022
    #5
    MelvMay likes this.

  6. oscarAbraham

    oscarAbraham

    Joined:
    Jan 7, 2013
    Posts:
    431
    oscarAbraham, Dec 24, 2022
    #6

  7. MelvMay

    MelvMay

    Unity Technologies

    Joined:
    May 24, 2013
    Posts:
    10,620
    You're best to quote the dev above, not me. I know how to use this stuff.

    Also, the dev is not using the Input System package and they are a beginner so that's not something they should jump into immediately.
     
    MelvMay, Dec 26, 2022
    #7
    oscarAbraham likes this.

  8. oscarAbraham

    oscarAbraham

    Joined:
    Jan 7, 2013
    Posts:
    431
    OK. You're right, sorry. I'll tag them: @rafaelgolu2005. Also, it is my personal opinion that the input system is not too hard to get started into; it's not as easy as the old ways, but I think you seem knowledgeable enough to use it if you need it.
     
    oscarAbraham, Dec 26, 2022
    #8