# CGFunctionEvaluateCallback Performs custom operations on the supplied input data to produce output data. ``` typealias CGFunctionEvaluateCallback = (UnsafeMutableRawPointer?, UnsafePointer, UnsafeMutablePointer) -> Void ``` ## Parameters `info` The `info` parameter passed to [`init(info:domainDimension:domain:rangeDimension:range:callbacks:)`](/documentation/CoreGraphics/CGFunction/init(info:domainDimension:domain:rangeDimension:range:callbacks:)). `inData` An array of floats. The size of the array is that specified by the `domainDimension` parameter passed to the [`init(info:domainDimension:domain:rangeDimension:range:callbacks:)`](/documentation/CoreGraphics/CGFunction/init(info:domainDimension:domain:rangeDimension:range:callbacks:)) function. `outData` An array of floats. The size of the array is that specified by the `rangeDimension` parameter passed to the [`init(info:domainDimension:domain:rangeDimension:range:callbacks:)`](/documentation/CoreGraphics/CGFunction/init(info:domainDimension:domain:rangeDimension:range:callbacks:)) function. ## Discussion The callback you write is responsible for implementing thecalculation of output values from the supplied input values. Forexample, if you want to implement a simple “squaring” functionof one input argument to one output argument, your evaluation functionmight be: ```objc void evaluateSquare(void *info, const float *inData, float *outData) { outData[0] = inData[0] * inData[0]; } ``` --- 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)