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# SCNBindingBlock

The signature for a block called for binding or unbinding a GLSL symbol in a custom program.

```
typealias SCNBindingBlock = (UInt32, UInt32, SCNNode?, SCNRenderer) -> Void
```

## Discussion

The block takes the following parameters:

- `programID`: The OpenGL program identifier for the current [`SCNProgram`](/documentation/SceneKit/SCNProgram) instance, as used by OpenGL functions such as `glValidateProgram`.
- `location`: The OpenGL location index for the symbol to be bound or unbound, as used by OpenGL functions such as `glUniform`.
- `renderedNode`: The [`SCNNode`](/documentation/SceneKit/SCNNode) object being rendered.
- `renderer`: The [`SCNRenderer`](/documentation/SceneKit/SCNRenderer) object responsible for rendering.

Call [`handleBinding(ofSymbol:handler:)`](/documentation/SceneKit/SCNShadable/handleBinding(ofSymbol:handler:)) or [`handleUnbinding(ofSymbol:handler:)`](/documentation/SceneKit/SCNShadable/handleUnbinding(ofSymbol:handler:)) to associate a handler block with a GLSL symbol for a SceneKit geometry or material.

---

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