我为一个基本的（FPS）播放器控制器编写了这个脚本，但是当跳转时它不工作。它工作了，但是很不稳定。下面是代码：

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

public class FirstPersonController : MonoBehaviour
{
    public CharacterController controller;
    public Transform groundCheck;
    public LayerMask groundMask;

    public int Speed;
    public float SprintMultipliyer = 2f;
    public float gravity = -9.81f;
    public float JumpHeight;
    public float groundDistance = 0.4f;

    private float a = 1f;
    private float SprintSpeed = 1;
    private float HorizontalInput;
    private float ForwardInput;

    bool IsonGround;

    Vector3 velocity;

    // Start is called before the first frame update
    void Start()
    {
        Cursor.lockState = CursorLockMode.Locked;
    }

    // Update is called once per frame
    void Update()
    {

        IsonGround = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);

        //this checks if the player is on the ground and his vertical [y] is less then 0 (which is good for a one height and not good for multiple different heights)
        if (IsonGround)
        {
            velocity.y = -3f;
        }
        //this if statement ischecking if the player presses [spacebar] and if he is on the ground
        if (Input.GetButtonDown("Jump") && IsonGround)
        {
            //the math for a jump is: the square root of the height you want to jump times [*] -2 * gravity or in the program: Mathf.Sqrt(JumpHeight * -2f * gravity);
            velocity.y = Mathf.Sqrt(JumpHeight * -2f * gravity);
        }

        if (Input.GetButton("Sprint") && IsonGround)
        {
            SprintSpeed = a * SprintMultipliyer;
        }
        else
        {
            SprintSpeed = 1;
        }
        

        //Input.GetAxis("[name of the axis]") is used to set the variables to 1 when the player presses [A/D] or [W/S]
        HorizontalInput = Input.GetAxis("Horizontal");
        ForwardInput = Input.GetAxis("Vertical");

        //this works by = transform is multiplied with HorizontalInput [A/D] and then multipliyng transform.forward with ForwardInput [W/S]
        Vector3 move = transform.right * HorizontalInput + transform.forward * ForwardInput;

        //controller is a public CharacterControler that is called [controller]
        //.Move is a function similar to transform.Translate
        //move is a Vector3 that is used for left/right and forward/backward input
        controller.Move(move * Speed * SprintSpeed * Time.deltaTime);

        velocity.y += gravity * Time.deltaTime;

        controller.Move(velocity * Time.deltaTime);
    }
}

我尝试改变重力，跳跃高度和地面距离，但仍然不能正确工作。地面距离对象也在地面上，地面在地面层上。