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# CGFunction

A general facility for defining and using callback functions.

```
class CGFunction
```

## Overview

These functions can take an arbitrary number of floating-point input values and pass back an arbitrary number of floating-point output values.

Core Graphics uses function objects to implement shadings. [`CGShading`](/documentation/CoreGraphics/CGShading) describes the parameters and semantics required for the callbacks used by function objects.

## Topics

### Creating Function Objects

[`init(info:domainDimension:domain:rangeDimension:range:callbacks:)`](/documentation/CoreGraphics/CGFunction/init(info:domainDimension:domain:rangeDimension:range:callbacks:))

Creates a Core Graphics function.

### Retaining and Releasing CGFunction Objects

[`CGFunctionRelease`](/documentation/CoreGraphics/CGFunctionRelease)

Decrements the retain count of a function object.

[`CGFunctionRetain`](/documentation/CoreGraphics/CGFunctionRetain)

Increments the retain count of a function object.

### Callbacks

[`CGFunctionCallbacks`](/documentation/CoreGraphics/CGFunctionCallbacks)

A structure that contains callbacks needed by a `CGFunctionRef` object.

[`CGFunctionEvaluateCallback`](/documentation/CoreGraphics/CGFunctionEvaluateCallback)

Performs custom operations on the supplied input data to produce output data.

[`CGFunctionReleaseInfoCallback`](/documentation/CoreGraphics/CGFunctionReleaseInfoCallback)

Performs custom clean-up tasks when Core Graphics deallocates a `CGFunctionRef` object.

### Working with Core Foundation Types

[`typeID`](/documentation/CoreGraphics/CGFunction/typeID)

Returns the type identifier for Core Graphics function objects.

## See Also

  [Quartz 2D Programming Guide](https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/Introduction/Introduction.html#//apple_ref/doc/uid/TP30001066)


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