<!--
{
  "availability" : [
    "iOS: 8.0.0 - 26.0.0",
    "iPadOS: 8.0.0 - 26.0.0",
    "macCatalyst: 13.1.0 - 26.0.0",
    "macOS: 10.8.0 - 26.0.0",
    "tvOS: 9.0.0 - 26.0.0",
    "visionOS: 1.0.0 - 26.0.0",
    "watchOS: 3.0.0 - 26.0.0"
  ],
  "documentType" : "symbol",
  "framework" : "SceneKit",
  "identifier" : "/documentation/SceneKit/SCNParticleSystem/birthDirection",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Property",
  "symbol" : {
    "kind" : "Instance Property",
    "modules" : [
      "SceneKit"
    ],
    "preciseIdentifier" : "c:objc(cs)SCNParticleSystem(py)birthDirection"
  },
  "title" : "birthDirection"
}
-->

# birthDirection

The possible initial directions for newly spawned particles, relative to the emitter shape.

```
var birthDirection: SCNParticleBirthDirection { get set }
```

## Discussion

This property defines initial directions for new particles relative to the geometry specified in the [`emitterShape`](/documentation/SceneKit/SCNParticleSystem/emitterShape) property. This property has no effect if the [`emitterShape`](/documentation/SceneKit/SCNParticleSystem/emitterShape) property value is `nil`.

For example, if the emitter shape is an [`SCNSphere`](/documentation/SceneKit/SCNSphere) geometry and the birth location is [`SCNParticleBirthDirection.surfaceNormal`](/documentation/SceneKit/SCNParticleBirthDirection/surfaceNormal), new particles radiate away from the center of the sphere. You can randomize the direction of newly spawned particles with the [`spreadingAngle`](/documentation/SceneKit/SCNParticleSystem/spreadingAngle) property.

The default value is [`SCNParticleBirthDirection.constant`](/documentation/SceneKit/SCNParticleBirthDirection/constant), specifying that all particles use the same base [`emittingDirection`](/documentation/SceneKit/SCNParticleSystem/emittingDirection) value.  For possible values, see [`SCNParticleBirthDirection`](/documentation/SceneKit/SCNParticleBirthDirection).

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)