# replaceVertices(at:commandBuffer:) Returns a Metal buffer you populate on the GPU with the new contents of the vertex buffer. ``` final func replaceVertices(at index: Int, commandBuffer: (any MTLCommandBuffer)?) -> any MTLBuffer ``` ## Parameters `index` The vertex buffer index to replace. `commandBuffer` The command buffer that writes to this buffer, or `nil` to skip synchronization. ## Return Value A `MTLBuffer` ready for GPU write operations. ## Discussion Upon return the buffer’s contents are undefined; the caller is responsible for populating it with valid data. The renderer waits for the provided command buffer to complete before using the buffer for rendering. --- 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)