LaunchArcRender.cs

// Launch Arc Renderer for Unity 3D from this Tutorial (with minor fixes):
// https://www.youtube.com/watch?v=iLlWirdxass

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

[RequireComponent (typeof(LineRenderer))]
public class LaunchArcRenderer : MonoBehaviour {

    LineRenderer lr;

    public float velocity = 10f;
    public float angle = 45f;
    
    [Range(1, 100)] public int resolution = 10;

    float gravity;
    float radianAngle;

    void Awake() {
        lr = GetComponent<LineRenderer>();
        gravity = Mathf.Abs(Physics2D.gravity.y);
    }

    void OnValidate() {
        if (lr != null && Application.isPlaying) {
            RenderArc();
        }
    }

    void Start() {
        RenderArc();
    }

    void RenderArc() {
        lr.positionCount = resolution + 1;
        lr.SetPositions(CalcArcArray());
    }

    Vector3[] CalcArcArray() {
        Vector3[] arcArray = new Vector3[resolution + 1];

        radianAngle = Mathf.Deg2Rad * angle;
        float maxDistance = (velocity * velocity * Mathf.Sin(2 * radianAngle)) / gravity;

        for (int i = 0; i <= resolution; i++) {
            float t = (float)i / (float)resolution;
            arcArray[i] = CalculateArcPoint(t, maxDistance);
        }
        return arcArray;
    }

    Vector3 CalculateArcPoint(float progressedDist, float maxDistance) {
        float x = progressedDist * maxDistance;
        float y = x * Mathf.Tan(radianAngle) - ((gravity * x * x) / (2 * velocity * velocity * Mathf.Cos(radianAngle) * Mathf.Cos(radianAngle)));
        return new Vector3(x, y, 0f);
    }
}