unity - - BetterJump

在unity实现跳跃的时候按下时间越长，跳跃高度越高的功能

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

public class PlayerControl : MonoBehaviour
{
    private Rigidbody2D rb;
    private Animator animator;
    public float speed = 10;
    public bool isGround,isJump;
    public Transform groundCheck;
    public LayerMask ground;
    public float jumpForce = 30;
    public float jumpTime,jumpTimeCounter;

    void Start()
    {
        rb = GetComponent();
        animator = GetComponent();
    }
    void Update()
    {
        float x = Input.GetAxisRaw("Horizontal");
        float y = Input.GetAxis("Vertical");
        if(x != 0)
            transform.localScale = new Vector3(x, 1 ,1);
        Vector2 dir = new Vector2(x,y);
        MoveMent(dir);

        //如果按下jump并且人物此时在地面，就可以跳跃
        if(Input.GetButtonDown("Jump") && isGround){
            isJump = true;
            jumpTimeCounter = jumpTime;
            Jump();
        }
        //跳跃持续增高
        if(Input.GetKey(KeyCode.Space) && isJump ){
            if(jumpTimeCounter>0){
                rb.velocity = new Vector2(rb.velocity.x,0);
                rb.velocity += Vector2.up * jumpForce;
                jumpTimeCounter -= Time.deltaTime;
            }
            else {
                isJump = false;
            }
        }
        if(Input.GetKeyUp(KeyCode.Space))
            isJump = false;
    }
    //判断是否在地面
    void FixedUpdate() {
        isGround = Physics2D.OverlapCircle(groundCheck.position,0.3f,ground);
    }
    void MoveMent(Vector2 dir)
    {
        //地面移动
        rb.velocity = new Vector2(dir.x*speed , rb.velocity.y);
        //rb.velocity = Vector2.Lerp(rb.velocity , (new Vector2(dir.x*speed , rb.velocity.y)) , Time.deltaTime);
    }
    //正常跳跃
    void Jump()
    {
        rb.velocity = new Vector2(rb.velocity.x,0);
        rb.velocity += Vector2.up * jumpForce;
    }
}