Unity c# 3D 在添加侧向移动时前后移动中断？

Question

Beginner question so please don't hate. I've made this 3d character controller script (I know it's terrible but I'm trying to begin with something I 100% understand before moving to more complex things). In this script, I made bools of wPressed, aPressed, sPressed, and dPressed in the update function. I then made the FixedUpdate function and added this section of code:

    if (wPressed == true)
    {
        player.velocity = transform.forward * movementSpeed;
    }

    if (sPressed == true)
    {
        player.velocity = -transform.forward * movementSpeed;
    }

    if (wPressed == false && sPressed == false)
    {
        player.velocity = transform.forward * 0;
    }

    if (wPressed == true && sPressed == true)
    {
        player.velocity = transform.forward * 0;
    }

Its probably bad... But it worked fine for now... However when I tried adding the a and d movement,

if (aPressed == true)
{
    player.velocity = -transform.right * movementSpeed;
}

if (dPressed == true)
{
    player.velocity = transform.right * movementSpeed;
}

if (aPressed == false && dPressed == false)
{
    player.velocity = transform.right * 0;
}

if (aPressed == true && dPressed == true)
{
    player.velocity = transform.right * 0;
}

It also worked, but it now broke the w and s movement script. Why is that?

Here is the entire code

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

public class PlayerMovement : MonoBehaviour
{
    bool dPressed;
    bool aPressed;
    bool wPressed;
    bool sPressed;
    Rigidbody player;
    private int movementSpeed;

    // Start is called before the first frame update
    void Start()
    {
        player = GetComponent<Rigidbody>();
        movementSpeed = 5;
    }

    // Update is called once per frame
    void Update()
    {
        if (Input.GetKey(KeyCode.W))
        {
            wPressed = true;
        }

        if (Input.GetKeyUp(KeyCode.W))
        {
            wPressed = false;
        }

        if (Input.GetKey(KeyCode.S)) 
        {
            sPressed = true;        
        }

        if (Input.GetKeyUp(KeyCode.S))
        {
            sPressed = false;
        }

        if (Input.GetKey(KeyCode.A)) 
        {
            aPressed = true;
        }

        if (Input.GetKeyUp(KeyCode.A))
        {
            aPressed = false;
        }

        if (Input.GetKey(KeyCode.D)) 
        {
            dPressed = true;
        }

        if (Input.GetKeyUp(KeyCode.D))
        {
            dPressed = false;        
        }
    }

    private void FixedUpdate()
    {
        if (wPressed == true)
        {
            player.velocity = transform.forward * movementSpeed;
        }

        if (sPressed == true)
        {
            player.velocity = -transform.forward * movementSpeed;
        }

        if (wPressed == false && sPressed == false)
        {
            player.velocity = transform.forward * 0;
        }

        if (wPressed == true && sPressed == true)
        {
            player.velocity = transform.forward * 0;
        }

        if (aPressed == true)
        {
            player.velocity = -transform.right * movementSpeed;
        }

        if (dPressed == true)
        {
            player.velocity = transform.right * movementSpeed;
        }

        if (aPressed == false && dPressed == false)
        {
            player.velocity = transform.right * 0;
        }

        if (aPressed == true && dPressed == true)
        {
            player.velocity = transform.right * 0;
        }


    }

}

Answer 1

Your issue is that whenever you have new input, you are fully overwriting your current velocity. For example, at every conditional statement, you have a

player.velocity = transform.direction * movementSpeed

Instead, you would want to isolate the velocity that each direction would change. I recommend looking into GetAxis , which is a similar approach but reduces the number of input checks.

float mH = Input.GetAxis ("Horizontal");
float mV = Input.GetAxis ("Vertical");
player.velocity = new Vector3 (mH * movementSpeed, rb.velocity.y, mV * movementSpeed);

Answer 2

You are always overwriting the entire velocity eg

player.velocity = transform.right * 0;

so even if w (or anything else) is pressed you set the entire velocity = 0,0,0. Forgetting all previously handled keys.

---

Rather do eg

private void Update()
{
    var movement = Vector2.zero;

    if (Input.GetKey(KeyCode.W))
    {
        movement.y += 1;
    }
    if(Input.GetKey(KeyCode.S))
    {
        movement.y -= 1;
    }

    if(Input.GetKey(KeyCode.A))
    {
        movement.x -= 1;
    }
    if(Input.GetKey(KeyCode.D))
    {
        movement.x += 1;
    }

    movement = Vector2.ClampMagnitude(movement, 1f);

    player.velocity = transform.forward * movement.y + transform.right * movement.x;
}

---

Note that by default Unity also provides this via GetAxis

var movement = new Vector2 (Input.GetAxis ("Horizontal"),  Input.GetAxis ("Vertical"));

movement = Vector2.ClampMagnitude(movement, 1f);

player.velocity = transform.forward * movement.y + transform.right * movement.x;

Answer 3

First of all, this section

if (aPressed == false && dPressed == false)
{
    player.velocity = transform.right * 0;
}

will execute always when (A == false && D == false) even if W/S are pressed too. Easy solution is just move this double-check section to the top.

More complex solution is create Vector3 for velocity and then make single player.velocity = newVec based on the input.

Vector3 dir = Vector3.zero;
var forward = transform.forward;
var right = transform.right;

if(aPressed)
  dir -= right;
if(dPressed)
  dir += right;
if(sPressed)
  dir -= forward;
if(wPressed)
  dir += forward;

//Same as Vector3.ClampMagnitude(vec, 1f) but a bit faster
dir = dir.normalized;
player.velocity = dir;

There is also Input.GetAxis solution, but be careful with it, because it can cause minor performance loss when called frequently (for instance 100-1000 times a frame)