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# instanceDescriptorBuffer

A buffer that contains descriptions of each instance in the acceleration structure.

```
var instanceDescriptorBuffer: (any MTLBuffer)? { get set }
```

## Discussion

You need to set a buffer before creating the instanced acceleration structure. The buffer needs to contain a list of instance data structures, each defining the characteristics of an instance. The descriptor’s [`instanceDescriptorType`](/documentation/Metal/MTLInstanceAccelerationStructureDescriptor/instanceDescriptorType) property determines which memory layout to use for the instance data; see [`MTLAccelerationStructureInstanceDescriptorType`](/documentation/Metal/MTLAccelerationStructureInstanceDescriptorType) for more information.

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