Check LowLevelPhysics2D API intersections

Note: This documentation is about writing C# scripts using the LowLevelPhysics2D API. To use 2D physics in the Unity Editor using components like the Rigidbody 2D component, refer to 2D physics instead.

To check whether 2D physics objects overlap or will collide, also known as intersections, use LowLevelPhysics2D API query methods.

Use one of the following methods:

• The PhysicsQuery API to check for overlaps. For example, PhysicsQuery.CapsuleAndCircle to check whether a capsule overlaps with a circle.
• The Intersect method of a geometry object to check if it overlaps with another geometry object. For example, CapsuleGeometry.Intersect.

The world object also has the following methods:

• Methods that cast rays or shapes. For example, PhysicsWorld.CastRay or PhysicsWorld.CastGeometry.
• Overlap test methods that return true if a point or shape overlaps another object. For example, PhysicsWorld.TestOverlapAABB.
• Overlap methods that return the objects that overlap a point or shape. For example, PhysicsWorld.OverlapCircle.

All methods are thread-safe. For more information, refer to Optimize the LowLevelPhysics2D API with multithreading.

Important: These methods return NativeArray types, which you must dispose of to free the memory they use. For more information, refer to Destroy objects and manage memory.

Example

To cast rays to check whether a shape will collide with other shapes, use the CastGeometry API.

For example, the following script checks if a small falling circle will collide with objects underneath it. Attach the script to a GameObjectThe 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 and enter Play mode, then use the Big Circle checkbox to toggle an object underneath the falling circle.

using UnityEngine;
using UnityEngine.LowLevelPhysics2D;
using Unity.Collections;

public class CastGeometryExample : MonoBehaviour
{
    private PhysicsWorld world;
    public bool BigCircle;

    void Start()
    {
        world = PhysicsWorld.defaultWorld;

        // Create a small falling circle
        CircleGeometry object1Geometry = CircleGeometry.Create(0.5f, new Vector2(0.5f, 8f));
        PhysicsBody object1 = world.CreateBody(new PhysicsBodyDefinition
        { 
            position = object1Geometry.center,
            type = PhysicsBody.BodyType.Dynamic
        });
        object1.CreateShape(object1Geometry);

        if (BigCircle)
        {
            // Create a larger static circle below
            CircleGeometry object2Geometry = CircleGeometry.Create(3f, new Vector2(0f, 0f));
            PhysicsBody object2 = world.CreateBody(new PhysicsBodyDefinition
            { 
                position = object2Geometry.center,
                type = PhysicsBody.BodyType.Static
            });
            object2.CreateShape(object2Geometry);
        }

        // Set translation and filter for the cast
        Vector2 translation = new Vector2(0, -10f); // Move downwards
        PhysicsQuery.QueryFilter filter = new PhysicsQuery.QueryFilter();

        // Cast the circle geometry through the world
        NativeArray<PhysicsQuery.WorldCastResult> results = world.CastGeometry(object1Geometry, translation, filter, PhysicsQuery.WorldCastMode.Closest, Allocator.Temp);

        if (results.Length > 0)
        {
            Debug.Log("Collision will occur!");
        }

        // Dispose of the NativeArray to free memory
        results.Dispose();
    }
}

Additional resources

• Introduction to collision in the LowLevelPhysics2D API
• PhysicsAABB