Physics Core 2D API workflow

Create a 2D scene that simulates physics using the Unity.U2D.Physics API.

Follow these steps:

1. Include the Unity.U2D.Physics library in a C# script.
2. Create a 2D physics world.
3. Create physics objects and add them to the world.
4. Configure objects with definitions.
5. Attach the script to a GameObject, then enter Play mode.

Include the Unity.U2D.Physics library

In a C# script, add using Unity.U2D.Physics; at the top to include the Unity.U2D.Physics library.

You can use the Unity.U2D.Physics API in any C# script, not only MonoBehaviour script files. But if you use a MonoBehaviour script file, you can configure physics properties in the Inspector window of a GameObject, move GameObjects, and attach sprites.

Create a 2D physics world

To add 2D physics objects, you first need to create a PhysicsWorld object to add them to. Do either of the following:

• Use the world Unity automatically creates.
• Create a new world.

For more information, refer to Create a physics world.

Create physics objects

To add physics objects to the world, do the following:

1. Create a PhysicsBody object, which defines the position, rotation, and velocity of an object. It doesn’t define an area.
2. Attach one or more PhysicsShape objects to the PhysicsBody, which define the area that interacts with other shapes. Unity also draws the shapes as a debug visualization.
3. Add the body to the world you created.

For more information, refer to Create a physics object.

Configure objects with definitions

To configure the properties of the world and its physics objects, create definition objects, for example PhysicsBodyDefinition. Definition objects contain properties like position and gravity that you can adjust in the Unity Editor, or pass into the object when you create it.

To configure the properties in the Inspector window, make the definition object a public field.

For more information, refer to Configure objects using definitions.

Attach the script to a GameObject

To start the simulation, you usually attach the script to a GameObject in your scene, then enter Play mode.

By default, physics objects don’t move a GameObject. To make a physics object update the Transform component of the GameObject, refer to Move a GameObject with the Physics Core 2D API.

To add a sprite, refer to Add a sprite to an object.

Example

The following example creates a small circle that falls under gravity onto a large circle. Attach the script to a GameObject in your scene, then enter Play mode.

using UnityEngine;
using Unity.U2D.Physics;

public class Example2DPhysics : MonoBehaviour
{
    void Start()
    {
        // Create the world
        PhysicsWorld world = PhysicsWorld.defaultWorld;

        // Create a body in the world, with a definition object that sets the position and enables physics
        PhysicsBody object1 = world.CreateBody(new PhysicsBodyDefinition
        { 
            position = new Vector2(0.5f, 8f),
            type = PhysicsBody.BodyType.Dynamic
        });

        // Attach a circle shape to the first body 
        PhysicsShape object1shape = object1.CreateShape(new CircleGeometry());

        // Create a second body in the world, with a definition object that sets the position and disables physics
        PhysicsBody object2 = world.CreateBody(new PhysicsBodyDefinition
        { 
            position = new Vector2(0f, 0f),
            type = PhysicsBody.BodyType.Static
        });

        // Attach a circle shape to the second body 
        object2.CreateShape(new CircleGeometry { 
            radius = 3f,
        });
    }
}

Additional resources

• PhysicsCore2D repository on GitHub