# copyParameterData(buffer:offset:) Copies the parameter data into the provided buffer. ``` func copyParameterData(buffer: any MTLBuffer, offset: Int) ``` ## Parameters `buffer` The buffer instance to copy the data into. It needs to have an [`MTLStorageMode.shared`](/documentation/Metal/MTLStorageMode/shared) storage mode, and there needs to be enough room in the buffer to store the data. `offset` The location in the buffer to copy the data to. The offset needs to be a multiple of the parameter alignment. ## Discussion To convert coordinate values inside your shader, pass the rate map data into the shader in an [`MTLBuffer`](/documentation/Metal/MTLBuffer) instance. The [`parameterDataSizeAndAlign`](/documentation/Metal/MTLRasterizationRateMap/parameterDataSizeAndAlign) property provides the size and alignment requirements for the buffer. You can convert between screen space and physical fragment space by binding the buffer to the shader with type `rasterization_rate_map_data`, then constructing `rasterization_rate_map_decoder` with the buffer data. For more details, see the “Variable Rasterization Rate” section of the [Metal Shading Language Specification](https://developer.apple.com/metal/Metal-Shading-Language-Specification.pdf). --- 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)