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# fieldBitMask

A mask that defines which categories of physics fields can exert forces on the particles.

```
var fieldBitMask: UInt32 { get set }
```

## Discussion

When a particle is inside the region of a [`SKFieldNode`](/documentation/SpriteKit/SKFieldNode) object, that field node’s [`categoryBitMask`](/documentation/SpriteKit/SKFieldNode/categoryBitMask) property is compared to the emitter’s [`fieldBitMask`](/documentation/SpriteKit/SKEmitterNode/fieldBitMask) property by performing a logical AND operation. If the result is a non-zero value, then the field node’s effect is applied to the particle as if it had a physics body. The physics body is assumed to have a [`mass`](/documentation/SpriteKit/SKPhysicsBody/mass) of `1.0` and a [`charge`](/documentation/SpriteKit/SKPhysicsBody/charge) of `1.0`

The default value is `0x00000000` (all bits cleared).

---

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