Move a GameObject with the Physics Core 2D API

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

• GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
  See in Glossary
• Add a sprite to a Physics Core 2D API object
• World definition reference for the Physics Core 2D API
• Body definition reference for the Physics Core 2D API