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Unity 3D Planetary Rigidbody Walker

0 Comments - Dec 5, 2019
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When creating a Player Controller, the gravity is usually applied in just one direction, which is down.

But what about gravity with a central point? This is a job for the planetary walker.

A planetary walker is a type of controller that allows the player to walk on a spherical object (just like the planets are giant spheres), with the center of gravity being in a center of the sphere.

Steps

Below are the steps to make a planetary rigidbody walker, with a central point of gravity:

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

  • Create a 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 Update()
    {
        // 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 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;
    }

    void OnCollisionStay()
    {
        grounded = true;
    }
}
  • Create a 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 a new GameObject and call it "Player"
  • Create a new Capsule, move it inside "Player" object and change its position to (0, 1, 0)
  • Remove Capsule Collider component from the Capsule
  • Move the 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 the Planet variable

Press Play and observe the Player align to the planet surface:

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