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Question by Zaid26194 · Jul 05, 2016 at 06:00 AM · mathf.clamp

Mathf.Clamp help required

Hello! I'm doing a project from this book called "Unity Game Development in 24 Hours" by Ben Tristem and Mike Geig. In Chapter 15 we use Mathf.Clamp to help keep the ship on screen. Here is the code - using UnityEngine; using System.Collections;

 public class ShipControlScript : MonoBehaviour {
     public float playerSpeed = 10f;
     public GameControl gameController;
     public GameObject bulletPrefab;
     public float reloadTime = 0.5f; //Bullets can fire every 0.5 seconds
     private bool invert = false;
     private float elapsedTime = 0;
 
     // Update is called once per frame
     void Update() {
         elapsedTime += Time.deltaTime;
 
         //Move player from left to right
         float xMovement = Input.GetAxis("Horizontal") * playerSpeed * Time.deltaTime;
         float xPosition = Mathf.Clamp(xMovement, -7f, 7f); //Keeps ship on screen
 
         if (invert){
             transform.Translate(xPosition * -1, 0f, 0f);
         }
         else{
             transform.Translate(xPosition, 0f, 0f);
         }
 
         if (Input.GetButtonDown("Shoot") && elapsedTime > reloadTime) {
             Vector3 spawnPos = transform.position;
             spawnPos += new Vector3(0, 1f, 0);
             Instantiate(bulletPrefab, spawnPos, Quaternion.identity);
 
             invert = !invert;
 
             elapsedTime = 0f;
         }
 
         if (reloadTime > 0.2f){
             reloadTime -= Time.deltaTime / 300;
         }
     }
 
     void OnTriggerEnter2D (Collider2D other){
         gameController.PlayerDied();
     }
 }

Thing is that ship doesn't stay within -7f and 7f. It continues on and on. I even copy pasted the code that they provided and the ship still isn't restricted. Any idea why? Thanks for any help in advance.

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avatar image Hellium · Jul 03, 2016 at 09:22 PM 0
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If you translate the transform, obviously, your ship can leave the screen. But if you define the position absolutely, your ship won't leave the screen

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Answer by tanoshimi · Jul 05, 2016 at 06:08 AM

If that's exactly how the code is written, there's a mistake in the book. You're using clamp to make sure that the value of xPosition is always within the range (-7,7):

 float xPosition = Mathf.Clamp(xMovement, -7f, 7f);

But "xPosition" does not represent the position of the ship on the screen. It is used to determine the amount by which the ship moves each frame:

 transform.Translate(xPosition, 0f, 0f);

I have found pretty much every book related to Unity disappointing and badly-edited. I recommend you click the Learn tab at the top of this page to follow the official tutorials instead.

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avatar image Zaid26194 · Jul 05, 2016 at 02:44 PM 0
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Thanks! I actually was skeptical of this myself but it's nice to get confirmation that the book was wrong.

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