# LowLevelBufferResource A GPU-managed buffer for arbitrary per-draw data such as uniforms and custom parameters. ``` final class LowLevelBufferResource ``` ## Overview Buffer contents can be read and written synchronously on the CPU via span-based accessors, or on the GPU by writing to a `MTLBuffer` returned by `replace(commandBuffer:)`. Create a `LowLevelBufferResource` using [`makeBufferResource(descriptor:)`](/documentation/RealityKit/LowLevelRenderContext/makeBufferResource(descriptor:)). ## Topics ### Inspecting the descriptor [`var descriptor: LowLevelBufferResource.Descriptor`](/documentation/RealityKit/LowLevelBufferResource/descriptor-swift.property) The descriptor used to create this buffer resource. [`struct Descriptor`](/documentation/RealityKit/LowLevelBufferResource/Descriptor-swift.struct) The capacity and alignment requirements for a buffer resource. ### Reading buffer contents [`func read(commandBuffer: (any MTLCommandBuffer)?) -> any MTLBuffer`](/documentation/RealityKit/LowLevelBufferResource/read(commandBuffer:)) Returns a Metal buffer containing the current contents of the buffer resource for GPU read operations. [`func read((RawSpan) throws(E) -> R) throws(E) -> R`](/documentation/RealityKit/LowLevelBufferResource/read(_:)) Reads the current contents of the buffer resource synchronously on the CPU. ### Replacing buffer contents [`func replace(commandBuffer: (any MTLCommandBuffer)?) -> any MTLBuffer`](/documentation/RealityKit/LowLevelBufferResource/replace(commandBuffer:)) Returns a Metal buffer you populate on the GPU with the new contents of the buffer resource. [`func replace((inout MutableRawSpan) throws(E) -> R) throws(E) -> R`](/documentation/RealityKit/LowLevelBufferResource/replace(_:)) Replaces the entire contents of the buffer resource synchronously on the CPU. ### Instance Methods [`func update((inout MutableRawSpan) throws(E) -> R) throws(E) -> R`](/documentation/RealityKit/LowLevelBufferResource/update(_:)) Updates the buffer resource in place synchronously on the CPU. --- 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)