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Unity 3D Planetary Rigidbody Walker

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When creating a Player Controller, the gravity is usually applied just in one direction, which is down.

But what if you need to allow player to walk along the circular object?

In this tutorial I will be showing how to create a Player Controller with a planetary gravity support.

So let's begin!

Steps

  • Open the Scene with your circular level (In my case I have a custom-made planet model and a custom Skybox from here)

  • Create new script, call it "SC_RigidbodyWalker" and paste the code below inside it:

SC_RigidbodyWalker.cs

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

[RequireComponent(typeof(Rigidbody))]
[RequireComponent(typeof(CapsuleCollider))]

public class SC_RigidbodyWalker : MonoBehaviour
{
    public float speed = 5.0f;
    public bool canJump = true;
    public float jumpHeight = 2.0f;
    public Camera playerCamera;
    public float lookSpeed = 2.0f;
    public float lookXLimit = 60.0f;

    bool grounded = false;
    Rigidbody r;
    Vector2 rotation = Vector2.zero;
    float maxVelocityChange = 10.0f;

    void Awake()
    {
        r = GetComponent<Rigidbody>();
        r.freezeRotation = true;
        r.useGravity = false;
        r.collisionDetectionMode = CollisionDetectionMode.ContinuousDynamic;
        rotation.y = transform.eulerAngles.y;

        Cursor.lockState = CursorLockMode.Locked;
        Cursor.visible = false;
    }

    void FixedUpdate()
    {
        if (grounded)
        {
            // Calculate how fast we should be moving
            Vector3 forwardDir = Vector3.Cross(transform.up, -playerCamera.transform.right).normalized;
            Vector3 rightDir = Vector3.Cross(transform.up, playerCamera.transform.forward).normalized;
            Vector3 targetVelocity = (forwardDir * Input.GetAxis("Vertical") + rightDir * Input.GetAxis("Horizontal")) * speed;

            Vector3 velocity = transform.InverseTransformDirection(r.velocity);
            velocity.y = 0;
            velocity = transform.TransformDirection(velocity);
            Vector3 velocityChange = transform.InverseTransformDirection(targetVelocity - velocity);
            velocityChange.x = Mathf.Clamp(velocityChange.x, -maxVelocityChange, maxVelocityChange);
            velocityChange.z = Mathf.Clamp(velocityChange.z, -maxVelocityChange, maxVelocityChange);
            velocityChange.y = 0;
            velocityChange = transform.TransformDirection(velocityChange);

            r.AddForce(velocityChange, ForceMode.VelocityChange);

            if (Input.GetButton("Jump") && canJump)
            {
               r.AddForce(transform.up * jumpHeight, ForceMode.VelocityChange);
            }
        }

        grounded = false;

        // Player and Camera rotation
        rotation.x += -Input.GetAxis("Mouse Y") * lookSpeed;
        rotation.x = Mathf.Clamp(rotation.x, -lookXLimit, lookXLimit);
        playerCamera.transform.localRotation = Quaternion.Euler(rotation.x, 0, 0);
        Quaternion localRotation = Quaternion.Euler(0f, Input.GetAxis("Mouse X") * lookSpeed, 0f);
        transform.rotation = transform.rotation * localRotation;
    }

    void OnCollisionStay()
    {
        grounded = true;
    }
}
  • Create new script, call it "SC_PlanetGravity" and paste the code below inside it:

SC_PlanetGravity.cs

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

public class SC_PlanetGravity : MonoBehaviour
{
    public Transform planet;
    public bool alignToPlanet = true;

    float gravityConstant = 9.8f;
    Rigidbody r;

    void Start()
    {
        r = GetComponent<Rigidbody>();
    }

    void FixedUpdate()
    {
        Vector3 toCenter = planet.position - transform.position;
        toCenter.Normalize();

        r.AddForce(toCenter * gravityConstant, ForceMode.Acceleration);

        if (alignToPlanet)
        {
            Quaternion q = Quaternion.FromToRotation(transform.up, -toCenter);
            q = q * transform.rotation;
            transform.rotation = Quaternion.Slerp(transform.rotation, q, 1);
        }
    }
}
  • Create new GameObject and call it "Player"
  • Create new Capsule, move it inside "Player" object and change its position to (0, 1, 0)
  • Remove Capsule Collider component from Capsule
  • Move Main Camera inside "Player" object and change its position to (0, 1.64, 0)
  • Attach SC_RigidbodyWalker script to "Player" object (You'll notice it will add additional components such as Rigidbody and Capsule Collider).
  • Change Capsule Collider Height to 2 and Center to (0, 1, 0)
  • Assign Main Camera to Player Camera variable in SC_RigidbodyWalker
  • Lastly attach SC_PlanetGravity script to "Player" object and assign your planet model to Planet variable

Press Play and observe the Player align to a planet surface.