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Question by David_Rios · May 22, 2017 at 10:30 PM · c#2dvelocity

Working on Ping Pong: Errors with keeping velocity constant

So I've been working on a Ping-Pong game project to learn, and I've been having issues because the ball sped up so much that it glitched out. So I tried putting a limit on velocity, and I got a few errors in the process. I tried solving it with updating the RigidBody2D code, but that ended up causing more errors. The 3 errors I received were:

Error CS1502: The best overloaded method match for UnityEngine.Vector2.ClampMagnitude(UnityEngine.Vector2, float) has some invalid arguments

Error CS1503: Argument #1 cannot convert float expression to type 'UnityEngine.Vector2'

Error CS0131: The left-hand side of an assignment must be a variable, a property or an indexer

Here's the source code of the script if needed. The language is C#:

 using UnityEngine;
 using System.Collections;
 
 public class BallControl : MonoBehaviour {
 
     private Rigidbody2D rb2d;
     private Vector2 vel;
     float maxVelocity = 10;
 
     void GoBall(){
         float rand = Random.Range (0.0f, 2.0f);
         if (rand < 1.0f) {
             rb2d.AddForce (new Vector2 (20.0f, -5.0f));
         } else {
             rb2d.AddForce (new Vector2 (-20.0f, -5.0f));
         }
     }
 
     // Use this for initialization
     void Start () {
         rb2d = GetComponent<Rigidbody2D>();
         Invoke("GoBall", 2.0f);
     }
 
     void FixedUpdate()    {
         GetComponent<rigidbody2D>() = Vector2.ClampMagnitude(GetComponent<Rigidbody2D>().velocity.magnitude, 
                 maxVelocity);
         }
 
     void ResetBall(){
         vel.y = 0;
         vel.x = 0;
         rb2d.velocity = vel;
         gameObject.transform.position = new Vector2(0, 0);
     }
 
     void RestartGame(){
         ResetBall();
         Invoke("GoBall", 1.0f);
     }
 
     void OnCollisionEnter2D (Collision2D coll) {
         if(coll.collider.CompareTag("Player")){
             vel.x = rb2d.velocity.x;
             vel.y = (rb2d.velocity.y / 2.0f) + (coll.collider.attachedRigidbody.velocity.y / 3.0f);
             rb2d.velocity = vel;
             if (coll.collider.CompareTag ("Wall")) {
                 vel.x = rb2d.velocity.x;
                 vel.y = (rb2d.velocity.y / 3.0f) + (coll.collider.attachedRigidbody.velocity.y / 3.0f);
                 rb2d.velocity = vel;
             }
         }
     }
 }






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Answer by Kishotta · May 22, 2017 at 11:08 PM

This appears to be the offending line: GetComponent<rigidbody2D>() = Vector2.ClampMagnitude(GetComponent<Rigidbody2D>().velocity.magnitude, maxVelocity)

You're getting type mismatches because you're passing the wrong type of data to this function, and trying to assign the result to a variable of the wrong type. Specifically, Vector2.ClampMagnitude takes in a Vector2 and a float. You are passing in two floats (the magnitude and the desired magnitude). As well, Vector2.ClampMagnitude returns a Vector2, which you are assigning to a Rigidbody2D variable.

What you want is:

 // cache this component because GetComponent is expensive
 // doing this in Start () or Awake () is even better
 Rigidbody2D rb2d = GetComponent<rigidbody2D> (); 
 
 // clamp the magnitude
 rb2d.velocity = Vector2.ClampMagnitude (rb2d.velocity, maxVelocity);

Edit Didn't see that you already have a rb2d variable. You can reuse that.

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