---
title: tangent
framework: scenekit
role: symbol
role_heading: Type Property
path: scenekit/scngeometrysource/semantic-swift.struct/tangent
---

# tangent

The semantic for surface tangent vector data.

## Declaration

```swift
static let tangent: SCNGeometrySource.Semantic
```

## Discussion

Discussion For a geometry source, this semantic identifies data containing the surface tangent vector at each vertex in the geometry. SceneKit uses this information to compute advanced lighting effects on the surface. For a custom shader program, you use this semantic to bind SceneKit’s vertex tangent data to an input attribute of the shader. Vertex tangent data is typically an array of three- or four-component vectors.

## See Also

### Advanced Shading Semantics

- [color](scenekit/scngeometrysource/semantic-swift.struct/color.md)