---
title: ForceEffectProtocol
framework: realitykit
role: symbol
role_heading: Protocol
path: realitykit/forceeffectprotocol
---

# ForceEffectProtocol

A protocol that defines a custom force effect.

## Declaration

```swift
protocol ForceEffectProtocol
```

## Overview

Overview A custom force effect is a function of a set of input rigid body attributes and returns force-like vector quantities. You can declare this custom force effect’s input types (parameterTypes) and output types (forceMode) by conforming to ForceEffectProtocol. For example, you can declare a custom force effect that depends on rigid bodies’ position and mass, and computes acceleration for each rigid body. struct MyCustomForce : ForceEffectProtocol {     var parameterTypes: PhysicsBodyParameterTypes { [.position, .mass] }     var forceMode: ForceMode = .acceleration     func update(parameters: inout ForceEffectParameters) {     } } Register your custom force effect to enable the physics system to compute forces affected by rigid bodies. MyCustomForce.register() At each physics update, the update(parameters:) method receives the declared inputs from ForceEffectParameters. You can set the output forces for each rigid body with setForce(_:index:). Sometimes, you may need to access properties from both your custom force effect and the current context while computing forces in the update function. The register(_:) method accepts an optional closure that allows you to capture the necessary properties. If you provide this closure to the register method, the update method is not required. struct MyCustomForceClosure: ForceEffectProtocol {     var forceMode: RealityFoundation.ForceMode = .force     var parameterTypes: PhysicsBodyParameterTypes { [.position, .mass] }     let customProperty: Double = 1 }

let contextualProperty: Double = 1

MyCustomForceClosure.register { event in     // Access the effect property via `event.effect.customProperty`.     // Access the input rigid body attributes via `event.parameters`.     // Access the contextual property directly by `contextualProperty`. }

## Topics

### Updating effects

- [update(parameters:)](realitykit/forceeffectprotocol/update(parameters:).md)
- [register(_:)](realitykit/forceeffectprotocol/register(_:)-1zt9t.md)
- [PhysicsBodyParameterTypes](realitykit/physicsbodyparametertypes.md)
- [ForceEffectParameters](realitykit/forceeffectparameters.md)
- [ForceEffectEvent](realitykit/forceeffectevent.md)
- [UnsafeForceEffectBuffer](realitykit/unsafeforceeffectbuffer.md)

### Instance Properties

- [forceMode](realitykit/forceeffectprotocol/forcemode.md)
- [parameterTypes](realitykit/forceeffectprotocol/parametertypes.md)

### Type Methods

- [register(_:)](realitykit/forceeffectprotocol/register(_:).md)

## Relationships

### Conforming Types

- [ConstantForceEffect](realitykit/constantforceeffect.md)
- [ConstantRadialForceEffect](realitykit/constantradialforceeffect.md)
- [DragForceEffect](realitykit/dragforceeffect.md)
- [RadialForceEffect](realitykit/radialforceeffect.md)
- [TurbulenceForceEffect](realitykit/turbulenceforceeffect.md)
- [VortexForceEffect](realitykit/vortexforceeffect.md)

## See Also

### Custom forces

- [ForceMode](realitykit/forcemode.md)
- [ForceEffectParameters](realitykit/forceeffectparameters.md)
- [ForceEffectBase](realitykit/forceeffectbase.md)