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Unity Engine

Move a GameObject with the Physics Core 2D API

Configure a 2D physics script to update the Transform component of a GameObject.
Read time 2 minutesLast updated 11 days ago
Note
This documentation is about writing C# scripts using the 
Unity.U2D.Physics
API. To use 2D physics in the Unity Editor using components like the Rigidbody 2D component, refer to 2D physics instead.
By default, when you create an object with the Physics Core 2D API, the object isn't connected to GameObjects in the scene.
To move a GameObject, configure the physics object to update the Transform component of the GameObject.
Follow these steps:
  1. To enable physics bodies updating Transform components globally, set the 
    TransformWriteMode
    property of the world to 
    Fast2D
     or 
    Slow2D
    .
  2. To enable the physics body updating Transform components, set its 
    TransformWriteMode
    to 
    Current
    .
  3. To attach the Transform component of the GameObject to the physics body, set the 
    transformObject
    property to the Transform component.
    Note
    The 
    transformObject
    property is available only in a C# script, not in the
    Inspector

    ?

    window of a public 
    PhysicsBodyDefinition
    object.
  4. Make sure the 
    type
    property of the physics body is set to 
    PhysicsBody.BodyType.Dynamic
    .
For example, attach the following script to a GameObject, then enter Play mode. The physics body falls under gravity, and updates the position in the Transform component in the Inspector window.
using UnityEngine;using Unity.U2D.Physics;public class MoveGameObject : MonoBehaviour{    public PhysicsWorld world;    public PhysicsWorldDefinition worldDefinition = PhysicsWorldDefinition.defaultDefinition;    void Awake()    {        // Enable physics bodies updating transforms        worldDefinition.transformWriteMode = PhysicsWorld.TransformWriteMode.Fast2D;        world = PhysicsWorld.Create(worldDefinition);    }        void Start()    {        // Create a body and shape         PhysicsBody circleBody = world.CreateBody();        CircleGeometry circleGeometry = new CircleGeometry { radius = 2f };        circleBody.CreateShape(circleGeometry);                // Set body to dynamic so it falls under gravity        circleBody.type = PhysicsBody.BodyType.Dynamic;         // Enable this physics body updating transforms        circleBody.transformWriteMode = PhysicsBody.TransformWriteMode.Current;        // Set the updated transform as the transform of this GameObject        circleBody.transformObject = transform;    }}

Rotate objects more quickly

By default, Unity sets a limit on how fast a physics body rotates, to avoid forces becoming too large and objects passing through each other incorrectly. To remove the limit, set the Fast Rotation Allowed property of the body to 
true
. This property is recommended only for circular objects.

Interpolate positions

By default, the physics body updates the Transform component after Unity finishes calculating the physics simulation. To interpolate positions between simulation steps instead, set the 
TransformWriteMode
of the physics body to 
Interpolate
or 
Extrapolate
.

Additional resources