# LowLevelInstanceTransformResource A GPU-managed buffer that stores an array of per-instance transforms for GPU instancing. ``` final class LowLevelInstanceTransformResource ``` ## Overview Assign a `LowLevelInstanceTransformResource` to a [`LowLevelMeshInstance`](/documentation/RealityKit/LowLevelMeshInstance) via [`setInstanceTransforms(_:)`](/documentation/RealityKit/LowLevelMeshInstance/setInstanceTransforms(_:)) to issue a single instanced draw call that renders multiple copies of the mesh. Each entry in the buffer is a `float4x4` model-to-local transform. The renderer computes the final world transform for each instance as `meshInstance.transform * instanceTransforms[i]`. Create a `LowLevelInstanceTransformResource` using [`makeInstanceTransformResource(instanceCapacity:)`](/documentation/RealityKit/LowLevelRenderContext/makeInstanceTransformResource(instanceCapacity:)). > Important: After creation, ``doc://com.apple.RealityKit/documentation/RealityKit/LowLevelInstanceTransformResource/instanceCount`` is `0`. Set it to the number of transforms > you write before rendering. ## Topics ### Inspecting instance counts [`var instanceCount: Int`](/documentation/RealityKit/LowLevelInstanceTransformResource/instanceCount) The number of active instances to draw. [`var instanceCapacity: Int`](/documentation/RealityKit/LowLevelInstanceTransformResource/instanceCapacity) The maximum number of instances the buffer holds. ### Reading transform data [`func read((consuming Span) throws(E) -> R) throws(E) -> R`](/documentation/RealityKit/LowLevelInstanceTransformResource/read(_:)) Reads the current transform data synchronously on the CPU. [`func read(commandBuffer: (any MTLCommandBuffer)?) -> any MTLBuffer`](/documentation/RealityKit/LowLevelInstanceTransformResource/read(commandBuffer:)) Returns a Metal buffer containing the current transform data for GPU read operations. ### Replacing transform data [`func replace((inout MutableSpan) throws(E) -> R) throws(E) -> R`](/documentation/RealityKit/LowLevelInstanceTransformResource/replace(_:)) Replaces all transform data synchronously on the CPU. [`func replace(commandBuffer: (any MTLCommandBuffer)?) -> any MTLBuffer`](/documentation/RealityKit/LowLevelInstanceTransformResource/replace(commandBuffer:)) Returns a Metal buffer you populate on the GPU with the new transform data. ### Instance Methods [`func update((inout MutableSpan) throws(E) -> R) throws(E) -> R`](/documentation/RealityKit/LowLevelInstanceTransformResource/update(_:)) Updates the transform data 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)