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# MTLAccelerationStructureMotionInstanceDescriptor

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

```
struct MTLAccelerationStructureMotionInstanceDescriptor
```

## Topics

### Creating an instance descriptor

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

Creates an acceleration-structure motion instance with default property values.

[`init(options:mask:intersectionFunctionTableOffset:accelerationStructureIndex:userID:motionTransformsStartIndex:motionTransformsCount:motionStartBorderMode:motionEndBorderMode:motionStartTime:motionEndTime:)`](/documentation/Metal/MTLAccelerationStructureMotionInstanceDescriptor/init(options:mask:intersectionFunctionTableOffset:accelerationStructureIndex:userID:motionTransformsStartIndex:motionTransformsCount:motionStartBorderMode:motionEndBorderMode:motionStartTime:motionEndTime:))

Creates an acceleration-structure motion instance with the property values you
provide.

### Specifying the instance

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

The index of an acceleration structure which applies to the next
acceleration-structure motion instance you create with the descriptor.

### Specifying motion data

[`motionStartTime`](/documentation/Metal/MTLAccelerationStructureMotionInstanceDescriptor/motionStartTime)

A starting time for the range of motion that the key-frame data represents.

[`motionEndTime`](/documentation/Metal/MTLAccelerationStructureMotionInstanceDescriptor/motionEndTime)

An ending time for the range of motion that the key-frame data represents.

[`motionStartBorderMode`](/documentation/Metal/MTLAccelerationStructureMotionInstanceDescriptor/motionStartBorderMode)

A behavior that configures how a motion instance handles timestamps
before a starting time.

[`motionEndBorderMode`](/documentation/Metal/MTLAccelerationStructureMotionInstanceDescriptor/motionEndBorderMode)

A behavior that configures how a motion instance handles timestamps
after an ending time.

[`motionTransformsStartIndex`](/documentation/Metal/MTLAccelerationStructureMotionInstanceDescriptor/motionTransformsStartIndex)

The index of motion data that represents the first key-frame motion data, which applies to
the next acceleration-structure motion instance you create with the descriptor.

[`motionTransformsCount`](/documentation/Metal/MTLAccelerationStructureMotionInstanceDescriptor/motionTransformsCount)

The number of motion data key-frames, which applies to
the next acceleration-structure motion instance you create with the descriptor.

### Customizing intersection and hit tests for the instance

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

An offset into the intersection-function table for ray tracing,
which applies to the next acceleration-structure motion instance you create
with the descriptor.

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

An option set which applies to the next acceleration structure motion-instance
you create with the descriptor.

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

A mask for testing ray-tracing rays with a scene’s geometry, which applies to
the next acceleration-structure motion instance you create with the descriptor.

### Specifying the user identifier

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

An unique identifier, which applies to the next acceleration-structure motion instance
you create with the descriptor.


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