No Gravity using RigidBody.MovePosition?

Hi everyone,

I've been doing a lot of reading and can't seem to find a solution to fit my situation. I'm creating a 2D platformer and have chosen to try character movement using rb.MovePosition (my first movement attempts were getting sprite jitters on collisions).

Everything is going okay except my guess is that gravity seems to be overridden by my movement function? I can move along X okay, but in the air my character controls more like a spaceship that falls very slowly. I.e. UpArrow moves me up, DownArrow moves down, no input = slow fall. Because of this my Jump inputs don't work either.

I used this video as the basis for my movement function. When the video demos rb.MovePosition, it doesn't seem to have the gravity problem.

Sorry my code is probably garbage, I'm new and only been at this for about three weeks. Any help would be greatly appreciated, I'm pulling my hair out over this!

RigidBody settings are all default

Code (CSharp):

1. public class RBMovement2D : MonoBehaviour
2. {
3.     Rigidbody2D rb;
4.     SpriteRenderer flip;
5.     SpriteRenderer starFlip;
6.  
7.     //Movement
8.     public float speed = 10.0f;
9.     Vector2 movement;
10.  
11.     //Jumping
12.     public bool isGrounded;
13.     private bool canJump;
14.     public float jumpPower;
15.  
16.     void Start()
17.     {
18.         rb = GetComponent<Rigidbody2D>();
19.         flip = GetComponent<SpriteRenderer>();
20.         starFlip = GameObject.Find("Stars").GetComponent<SpriteRenderer>();
21.  
22.     }
23.  
24.     void Update()
25.     {
26.         //Inputs ===================
27.  
28.         //GetAxis
29.         movement = new Vector2(Input.GetAxis("Horizontal"), Input.GetAxis("Vertical"));
30.      
31.         //Jumping
32.         if (isGrounded && ((Input.GetKeyDown(KeyCode.Space)) || (Input.GetKeyDown(KeyCode.UpArrow))))
33.         {
34.             canJump = true;
35.         }
36.         else
37.         {
38.             canJump = false;
39.         }
40.  
41.         //Flip Sprite X ======================
42.         if (Input.GetKey("right"))
43.         {
44.             flip.flipX = false;
45.             starFlip.flipX = false;
46.         }
47.         else if (Input.GetKey("left"))
48.         {
49.             flip.flipX = true;
50.             starFlip.flipX = true;
51.         }
52.  
53.  
54.     }
55.  
56.     private void FixedUpdate()
57.     {
58.         moveCharacter(movement);
59.     }
60.  
61.     private void moveCharacter(Vector2 direction)
62.     {
63.         //Movement
64.         rb.MovePosition((Vector2)transform.position + (direction * speed * Time.fixedDeltaTime));
65.      
66.         //Jumping
67.         if (canJump)
68.         {
69.             rb.AddForce(new Vector2(0, jumpPower), ForceMode2D.Impulse);
70.         }
71.     }
72.  
73.     private void OnTriggerEnter2D(Collider2D col)
74.     {
75.         if (col.tag.Contains("Ground"))
76.         {
77.             isGrounded = true;
78.         }
79.     }
80.  
81.     private void OnTriggerExit2D(Collider2D col)
82.     {
83.             isGrounded = false;
84.  
85.     }
86. }

 

not checked but maybe increase gravity if object falls too slowly

 

If I up the Gravity Scale, jumping seems to become impossible without using huge AddForce values. Slopes also become very sluggish

 

alternate add downforce when not grounded and release jump key

 

Thank you for your replies, but applying downward force after a jump... is that really the best solution? RigidBody's are supposed to respond to gravity, so if you have to program your own gravity wouldn't it be better to just use no RigidBody?

My understanding is that rb.MovePosition resets the rb.velocity each FixedUpdate. So how do you use rb.MovePosition without constantly reseting the rb.velocity.y?

 

as i understand sir all work - except object not falling fast enough, so either increase gravity and adjust other settings or add downforce??

 

Thank you for your reply!

To give you a sense of how I got to this point: I started off with a character controller using transform.translate for movement, but then found that the sprite "jitters" upon collision because (to my understanding) you're forcing the Game Object into a collider that then "rejects" the RigidBody2D during the physics step. Solutions I've read recommend moving the RigidBody to solve this issue using either AddForce (not very smooth, but commonly used for jumping?), Velocity, or MovePosition, but now rb.velocity and rb.moveposition are creating gravity issues. I've also read that you can still use transform.translate and solve sprite jitters using Raycasts, but I'm not sure that's the best way to do things for a simple 2D Platformer.

So according to your answer, you're saying that I could still use rb.moveposition on a dynamic rb, so long as I pass in (Physics2D.gravity * rb.gravityScale) somewhere? I think that this line of code is the culprit:

Code (CSharp):

1. rb.MovePosition((Vector2)transform.position + (direction * speed * Time.fixedDeltaTime));

If that's true, could you please show me how to "add the gravity term to [my] target position"? I've been trying to do that with my limited knowledge, but I'm still at a loss (again please forgive my ignorance, as I'm only 3 weeks into learning Unity/C#), and my own research is coming up empty.

Thank you for your help!

 

Thank you, that seems to have fixed things! Movement is a little janky (the character feels very heavy), but that at least gives me a good starting point. Thanks!