# LowLevelBuffer ``` final class LowLevelBuffer ``` ## Topics ### Structures [`struct Descriptor`](/documentation/RealityKit/LowLevelBuffer/Descriptor-swift.struct) ### Initializers [`init(descriptor: LowLevelBuffer.Descriptor) throws`](/documentation/RealityKit/LowLevelBuffer/init(descriptor:)) ### Instance Properties [`var bytesUsed: Int`](/documentation/RealityKit/LowLevelBuffer/bytesUsed) [`let descriptor: LowLevelBuffer.Descriptor`](/documentation/RealityKit/LowLevelBuffer/descriptor-swift.property) ### Instance Methods [`func read(using: any MTLCommandBuffer) -> any MTLBuffer`](/documentation/RealityKit/LowLevelBuffer/read(using:)) Retrieve the current contents of the buffer, for GPU reading. [`func replace(using: any MTLCommandBuffer) -> any MTLBuffer`](/documentation/RealityKit/LowLevelBuffer/replace(using:)) Retrieve an MTLBuffer that can be used to replace the contents of the buffer on GPU using Metal. [`func replaceUnsafeMutableBytes((UnsafeMutableRawBufferPointer) -> Void)`](/documentation/RealityKit/LowLevelBuffer/replaceUnsafeMutableBytes(_:)) Replace the buffer’s contents synchronously on the CPU. [`func withUnsafeBytes((UnsafeRawBufferPointer) -> Void)`](/documentation/RealityKit/LowLevelBuffer/withUnsafeBytes(_:)) Read the buffer synchronously on the CPU. The buffer provided is only valid for the lifetime of the callback. [`func withUnsafeMutableBytes((UnsafeMutableRawBufferPointer) -> Void)`](/documentation/RealityKit/LowLevelBuffer/withUnsafeMutableBytes(_:)) Update the buffer’s contents synchronously on the CPU. The buffer provided is only valid for the lifetime of the callback. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)