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# screenSpaceAmbientOcclusionBias

An offset for modulating ambient occlusion effects.

```
var screenSpaceAmbientOcclusionBias: CGFloat { get set }
```

## Discussion

Ambient occlusion is an effect that improves material shading by calculating the amounts of ambient light that reach various parts of a surface, creating shadows on parts of a geometry where incoming light is obscured by other parts of the geometry. (You can provide pre-rendered ambient occlusion effects for a material using its [`ambientOcclusion`](/documentation/SceneKit/SCNMaterial/ambientOcclusion) property.) *Screen-space ambient occlusion* (SSAO) provides a real-time approximation of this effect for the entire scene viewed through the camera.

This [`screenSpaceAmbientOcclusionBias`](/documentation/SceneKit/SCNCamera/screenSpaceAmbientOcclusionBias) value is used in an intermediate stage of calculating the SSAO effect, and measures a distance in scene units. Increasing or decreasing this value from its default of 0.03 can help to offset unrealistic effects produced by changing other SSAO settings.

---

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