Dynamically creating new Line Renderers causes strange Assertion Failed errors

Scripting
1

The code below, when attached to any gameObject, like a cube, is meant to move it around using the WASD keys and create a trail line behind it while holding the F button down. Creating the first line works fine but for some reason attempting to create a second line causes weird Assertion Failed errors and the line gets rendered at seemingly random places.

The errors I’m getting (which are repeated numerous times in the console):

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class LinerendererTest : MonoBehaviour {

    public float movementSpeed = 0.1f;
    LineRenderer currentLine;
    int numPoints;
   
    // Update is called once per frame
    void Update () {
        if (Input.GetKeyDown(KeyCode.F))
        {
            GameObject newLine = new GameObject();
            currentLine = newLine.AddComponent<LineRenderer>();
            currentLine.startWidth = 0.1f;
            currentLine.endWidth = 0.1f;
        }
        else if (Input.GetKey(KeyCode.F))
        {
            currentLine.numPositions = numPoints + 1;
            currentLine.SetPosition(numPoints, transform.position);
            numPoints++;
        }

        //Movement
        if (Input.GetKey(KeyCode.W))
        {
            transform.Translate(transform.forward * movementSpeed);
        }
        if (Input.GetKey(KeyCode.D))
        {
            transform.Translate(transform.right * movementSpeed);
        }
        if (Input.GetKey(KeyCode.S))
        {
            transform.Translate(-transform.forward * movementSpeed);
        }
        if (Input.GetKey(KeyCode.A))
        {
            transform.Translate(-transform.right * movementSpeed);
        }
        if (Input.GetKey(KeyCode.Space))
        {
            transform.Translate(transform.up * movementSpeed);
        }
        if (Input.GetKey(KeyCode.LeftShift))
        {
            transform.Translate(-transform.up * movementSpeed);
        }
    }
}

You can recreate this issue by copying the script above and adding it to a primitive cube game object. Move the cube around using WASD, and at the same time press and hold F to create lines behind the cube as you move it. You’ll notice that the bug happens the second time you create the line.

Any prompt help would be really appreciated.

2

Yep yep. I tested it to be sure (it was what I thought). Here is an updated snippet with the relevant pieces that I modified to get it working :slight_smile:

        if (Input.GetKeyDown(KeyCode.F))
        {
            GameObject newLine = new GameObject();
            currentLine = newLine.AddComponent<LineRenderer>();
            currentLine.startWidth = 0.1f;
            currentLine.endWidth = 0.1f;
            currentLine.positionCount = 1;
            numPoints = 0;
            currentLine.SetPosition(numPoints, transform.position);
        }
        else if (Input.GetKey(KeyCode.F))
        {
            numPoints++;
            currentLine.positionCount = numPoints + 1;
            currentLine.SetPosition(numPoints, transform.position);
        }
1 Like
3

That worked, thank you very much! And wow it’s pretty obvious now that I look at it. numPoints was never reset whenever a new line was created.

4

Indeed :slight_smile: ‘positionCount’ was also to replace the obsolete ‘numPositions’. :slight_smile:
Glad you got it working.