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# MTLAccelerationStructureUserIDInstanceDescriptor

A description of an instance in an instanced geometry acceleration structure, with the instance including a user identifier for the instance.

```
struct MTLAccelerationStructureUserIDInstanceDescriptor
```

## Topics

### Creating an instance descriptor

[`init()`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/init())

Creates a default acceleration structure instance.

[`init(transformationMatrix:options:mask:intersectionFunctionTableOffset:accelerationStructureIndex:userID:)`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/init(transformationMatrix:options:mask:intersectionFunctionTableOffset:accelerationStructureIndex:userID:))

Creates a new acceleration structure instance.

### Specifying the instance

[`accelerationStructureIndex`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/accelerationStructureIndex)

The index of the acceleration structure to use for the instance.

### Specifying the instance transform

[`transformationMatrix`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/transformationMatrix)

The transform for placing and orienting the instance in the scene.

### Customizing intersection and hit tests for the instance

[`intersectionFunctionTableOffset`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/intersectionFunctionTableOffset)

An offset for determining which function in the intersection function table Metal calls when testing a ray against the instance.

[`options`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/options)

The options for the instance.

[`mask`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/mask)

A mask to use for the instance when testing a ray against the geometry.

### Specifying the user identifier

[`userID`](/documentation/Metal/MTLAccelerationStructureUserIDInstanceDescriptor/userID)

The user identifier for the instance.


---

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