PhysicsJoint

Description

A joint is used to constrain bodies to the world or to each other in various ways. A joint is automatically destroyed when either body it is attached to is destroyed. A joint cannot exist unattached from a body.

Connect or constrain two bodies by creating a joint between them. For example, create a fixed joint to weld two bodies together, or a distance joint to keep them a set distance apart. Use joints to simulate real-world mechanical behaviors like a spring or a hinge. All joints let you set the anchor points on the bodies they connect, and limits on the force and torque they apply. Create two PhysicsBody objects, create a definition object for the joint type you want, for example PhysicsDistanceJointDefinition, then pass the definition into PhysicsWorld.CreateJoint. If you destroy a body, Unity also destroys any joints connected to it.

Additional resources: JointType, PhysicsDistanceJointDefinition

 // Use a fixed distance joint to create a fixed point that a large circle swings from.
 using UnityEngine;
 using Unity.U2D.Physics;

 public class CreateJointExample : MonoBehaviour
 {
     public PhysicsDistanceJointDefinition jointDefinition = new PhysicsDistanceJointDefinition();

     void Awake()
     {
         PhysicsWorld world = PhysicsWorld.defaultWorld;

         // Create a static fixed body.
         PhysicsBodyDefinition bodyDefinition1 = new PhysicsBodyDefinition
         {
             type = PhysicsBody.BodyType.Static,
             position = new Vector2(-5f, 0f),
         };
         PhysicsBody object1 = world.CreateBody(bodyDefinition1);

         // Create a large circle below the fixed body.
         PhysicsBodyDefinition bodyDefinition2 = new PhysicsBodyDefinition
         {
             type = PhysicsBody.BodyType.Dynamic,
             position = new Vector2(5f, 0f),
         };
         PhysicsBody object2 = world.CreateBody(bodyDefinition2);
         object2.CreateShape(new CircleGeometry { radius = 3f });

         // Add the bodies to the joint definition.
         jointDefinition.bodyA = object1;
         jointDefinition.bodyB = object2;

         // Add the joint to the world.
         world.CreateJoint(jointDefinition);
     }
 }

Properties

Constructors

Public Methods

Static Methods