Am I not understanding the Line Renderer, or simply bad at math? [Bullet Trails]

Unity Engine
1

Hey, so I’m trying to make bullet trails with the line renderer. Im raycasting for bullets, so its not actual trails, more like line segments showing up for a brief second at a semi-random place on the direction Vector of the shot fired. However, my code is not producing the results I was hoping. I’m a little tried, so maybe I just dun goofed in the math. Anyhow heres the logic

  • Raycast outwards, save hit information
  • save direction vector from Line Renderer (placed at the end of the barrel of the gun) to the hit point
  • Turn on the line renderer intermittently, and set the starting point of a line to be on the direction vector * some scalar
  • set the end point of the line renderer to be on the direction vector, but with some scalar *2
  • When done displaying, move faaar faaar away to Vector3(10000,10000,10000)

And heres the code:

public lineRenderer line;
public Vector2 bulletTrailLengthMinMax;
private bool bulleTrailAvailable;

 if(Physics.Raycast (ray, out hit, Mathf.Infinity)){

            Quaternion rot= Quaternion.FromToRotation(Vector3.up, hit.normal);

                 hit.collider.gameObject.SendMessage("WasShot",damagePerShot,SendMessageOptions.DontRequireReceiver);
			
			if (Random.value * 100f <= chanceOfBulletTrail  bulletTrailAvailable ) {
				hitVector = hit.point - line.transform.position;
				StartCoroutine(DrawBulletTrail());
				
				
			}
      

        }

     StartCoroutine(CoolDown());

    }
	
	private IEnumerator DrawBulletTrail()
	{
		bulletTrailAvailable = false;
		float startPoint = Random.Range(0.1f,0.5f); 
		float lineLenght = Random.Range(bulletTrailLengthMinMax.x*hitVector.sqrMagnitude,bulletTrailLengthMinMax.y*hitVector.sqrMagnitude);
		line.SetPosition(0,line.transform.position+hitVector * startPoint );
		line.SetPosition(1,line.transform.position+hitVector * lineLenght);
		yield return new WaitForSeconds(Time.deltaTime*2f);		 
		//line.SetPosition(0,new Vector3(10000,10000,10000));
		//line.SetPosition(1,new Vector3(10000,10000,10000));
		
		bulletTrailAvailable = true;
		
	}

This, for some reason draws hugely long line segments (they sometimes go backwards through the player).

Im probably screwing up this simple math, could someone check the logic for me?

2

you’re using the sqrmagnitudes when you set lineLenght… I think you might be wanting to use the actual magnitudes here.

3

I think an easier way to do this is to save the normal vector direction, hit point and distance.

normal = (hit.point - transform.position).normalized;
position = hit.position;
distance = Vector3.Distance(hit.point, transform.position);

Then set the points at hit.point * scalar of the normalized vector

randomLength = Random.Range (3F, 6F);
random = Random.Range(0 + randomLength, distance - randomLength);

line.SetPosition(0,  position - (random * normal) - (randomLength * normal));
line.SetPosition(1, position - (random * normal));

Something like that. And instead of moving the linerender to hell. Just set its vertex count to 0 when it is not used, and 2 when you use it…

4

Dammit, both responses seem to use an actual magnitude or a Vector3.distance. I dont think this would be a good thing, since this happens ALOT (this is a machine gun). I will try and implement the changes, see if it works. If it does, I know what the problem was, but will probably have to find another way :slight_smile: Thanks for input though

5

Well it was because I was not using the proper distances. I’ll stick with Vector3.distance for now, since it seems slightly faster than (a-b).magnitude. Thanks for the help!