---
title: MDLMaterialSemantic.ambientOcclusion
framework: modelio
role: symbol
role_heading: Case
path: modelio/mdlmaterialsemantic/ambientocclusion
---

# MDLMaterialSemantic.ambientOcclusion

The attenuation of ambient light due to local geometry variations on a surface.

## Declaration

```swift
case ambientOcclusion
```

## Discussion

Discussion Ambient occlusion (AO) describes the accessibility of a point on a surface to the surrounding radiant environment and is typically used to attenuate ambient lighting. A renderer should not use AO data should to affect direct illumination. Model I/O uses this semantic for the ao and map_ao attributes when importing from the MTL file format (for assets in the OBJ file format).

## See Also

### Constants

- [MDLMaterialSemantic.baseColor](modelio/mdlmaterialsemantic/basecolor.md)
- [MDLMaterialSemantic.subsurface](modelio/mdlmaterialsemantic/subsurface.md)
- [MDLMaterialSemantic.metallic](modelio/mdlmaterialsemantic/metallic.md)
- [MDLMaterialSemantic.specular](modelio/mdlmaterialsemantic/specular.md)
- [MDLMaterialSemantic.specularExponent](modelio/mdlmaterialsemantic/specularexponent.md)
- [MDLMaterialSemantic.specularTint](modelio/mdlmaterialsemantic/speculartint.md)
- [MDLMaterialSemantic.roughness](modelio/mdlmaterialsemantic/roughness.md)
- [MDLMaterialSemantic.anisotropic](modelio/mdlmaterialsemantic/anisotropic.md)
- [MDLMaterialSemantic.anisotropicRotation](modelio/mdlmaterialsemantic/anisotropicrotation.md)
- [MDLMaterialSemantic.sheen](modelio/mdlmaterialsemantic/sheen.md)
- [MDLMaterialSemantic.sheenTint](modelio/mdlmaterialsemantic/sheentint.md)
- [MDLMaterialSemantic.clearcoat](modelio/mdlmaterialsemantic/clearcoat.md)
- [MDLMaterialSemantic.clearcoatGloss](modelio/mdlmaterialsemantic/clearcoatgloss.md)
- [MDLMaterialSemantic.emission](modelio/mdlmaterialsemantic/emission.md)
- [MDLMaterialSemantic.bump](modelio/mdlmaterialsemantic/bump.md)