ジャンプと、それを成立させる接地判定

// CharacterController: you own gravity, so you own the jump too.
verticalSpeed = Mathf.Sqrt(jumpHeight * -2f * gravity);

// Rigidbody: hand it an impulse and let physics do the arc.
rb.AddForce(Vector3.up * jumpForce, ForceMode.Impulse);

using UnityEngine;

[RequireComponent(typeof(CharacterController))]
public class Jump : MonoBehaviour
{
    public Transform groundCheck;
    public LayerMask groundLayer;
    public float checkRadius = 0.25f;
    public float jumpHeight = 2f;
    public float gravity = -20f;

    // A jump the player asked for a moment too early still counts.
    public float bufferTime = 0.12f;
    // So does one asked for a moment after walking off an edge.
    public float coyoteTime = 0.12f;

    CharacterController cc;
    float verticalSpeed, lastGrounded, lastPressed;

    void Awake() => cc = GetComponent<CharacterController>();

    void Update()
    {
        bool grounded = Physics.CheckSphere(
            groundCheck.position, checkRadius, groundLayer, QueryTriggerInteraction.Ignore);

        if (grounded) lastGrounded = Time.time;
        if (Input.GetButtonDown("Jump")) lastPressed = Time.time;

        if (grounded && verticalSpeed < 0f) verticalSpeed = -2f;

        if (Time.time - lastPressed < bufferTime && Time.time - lastGrounded < coyoteTime)
        {
            verticalSpeed = Mathf.Sqrt(jumpHeight * -2f * gravity);
            lastPressed = lastGrounded = -99f;   // spend both, so it fires once
        }

        verticalSpeed += gravity * Time.deltaTime;
        cc.Move(Vector3.up * verticalSpeed * Time.deltaTime);
    }

    // Draw the check in the Scene view, so you can see what it is testing.
    void OnDrawGizmosSelected()
    {
        if (groundCheck == null) return;
        Gizmos.color = Color.green;
        Gizmos.DrawWireSphere(groundCheck.position, checkRadius);
    }
}