ID/Assets/Code/Lab5/Projectile.cs

using UnityEngine;

namespace Code.Lab5
{
    public class Projectile : MonoBehaviour
    {
        private bool _set;
        private Vector3 _firePos;
        private Vector3 _direction;
        private float _speed;
        private float _timeElapsed;

        private void Update()
        {
            if (!_set)
                return;

            _timeElapsed += Time.deltaTime;

            transform.position = _firePos + _direction * (_speed * _timeElapsed);
            transform.position += Physics.gravity * (_timeElapsed * _timeElapsed) / 2.0f;

            if (transform.position.y < -1.0f)
            {
                Destroy(gameObject);
            }
        }

        public void Set(Vector3 firePos, Vector3 direction, float speed)
        {
            _firePos = firePos;
            _direction = direction.normalized;
            _speed = speed;
            transform.position = firePos;
            _set = true;
            _timeElapsed = 0f;
        }

        private float GetLandingTime(float height = 0.0f)
        {
            var position = transform.position;

            var valueInt = _direction.y * _direction.y * (_speed * _speed);
            valueInt -= Physics.gravity.y * 2 * (position.y - height);

            if (valueInt < 0)
                return -1.0f;
                
            valueInt = Mathf.Sqrt(valueInt);
            
            var valueAdd = -_direction.y * _speed;
            var valueSub = -_direction.y * _speed;
            
            valueAdd = (valueAdd + valueInt) / Physics.gravity.y;
            valueSub = (valueSub - valueInt) / Physics.gravity.y;

            if (float.IsNaN(valueAdd) && !float.IsNaN(valueSub))
                return valueSub;
            if (!float.IsNaN(valueAdd) && float.IsNaN(valueSub))
                return valueAdd;
            if (float.IsNaN(valueAdd) && float.IsNaN(valueSub))
                return -1.0f;

            var time = Mathf.Max(valueAdd, valueSub);
            return time;
        }
        
        public Vector3 GetLandingPos(float height = 0.0f)
        {
            var landingPos = Vector3.zero;
            var time = GetLandingTime(height);
            
            if (time < 0.0f)
                return landingPos;
            
            landingPos.y = height;
            landingPos.x = _firePos.x + _direction.x * _speed * time;
            landingPos.z = _firePos.z + _direction.z * _speed * time;
            
            return landingPos;
        }
        
        public static Vector3 GetFireDirection(Vector3 startPos, Vector3 endPos, float speed, bool useHighTrajectory = false)
        {
            var direction = Vector3.zero;
            var delta = endPos - startPos;

            var a = Vector3.Dot(Physics.gravity, Physics.gravity);
            var b = -4 * (Vector3.Dot(Physics.gravity, delta) + speed * speed);
            var c = 4 * Vector3.Dot(delta, delta);

            var discriminant = b * b - 4 * a * c;
            if (discriminant < 0)
                return direction;

            var sqrtDiscriminant = Mathf.Sqrt(discriminant);
            
            var time0 = Mathf.Sqrt((-b + sqrtDiscriminant) / (2 * a));
            var time1 = Mathf.Sqrt((-b - sqrtDiscriminant) / (2 * a));

            float time;
            
            switch (time0)
            {
                case < 0.0f when time1 < 0.0f:
                    return direction;
                case < 0.0f:
                    time = time1;
                    break;
                default:
                {
                    if (time1 < 0.0f)
                        time = time0;
                    else
                    {
                        time = useHighTrajectory ? Mathf.Max(time0, time1) : Mathf.Min(time0, time1);
                    }

                    break;
                }
            }

            direction = 2 * delta - Physics.gravity * (time * time);
            direction /= 2 * speed * time;
            
            return direction.normalized;
        }
        
        public static bool IsTargetReachable(Vector3 startPos, Vector3 endPos, float speed)
        {
            var delta = endPos - startPos;
            
            var a = Vector3.Dot(Physics.gravity, Physics.gravity);
            var b = -4 * (Vector3.Dot(Physics.gravity, delta) + speed * speed);
            var c = 4 * Vector3.Dot(delta, delta);
            
            return b * b - 4 * a * c >= 0;
        }
        
        public static float GetMinimumSpeed(Vector3 startPos, Vector3 endPos)
        {
            var delta = endPos - startPos;

            var gravityMagnitude = Physics.gravity.magnitude;
            var deltaMagnitude = delta.magnitude;
            var deltaY = delta.y;

            var minSpeedSqr = gravityMagnitude * (deltaY + Mathf.Sqrt(deltaY * deltaY + deltaMagnitude * deltaMagnitude));
            
            return Mathf.Sqrt(minSpeedSqr);
        }
    }
}