# timingFunction A block used to customize the timing function. ``` var timingFunction: SKActionTimingFunction { get set } ``` ## Discussion If a timing function is provided, after the normal timing mode is applied, the result is sent to the timing function. The return [`SKActionTimingFunction`](/documentation/SpriteKit/SKActionTimingFunction) value of the timing function determines the actual time used to perform the animation. The following code shows how you can create a custom timing function using interpolation: ```swift import simd let horizontalAction = SKAction.moveTo(x: end.x, duration: 2.0) horizontalAction.timingFunction = { time in return simd_smoothstep(0, 1, time) } ``` If the above code is combined with a vertical linear move action, the path taken by a node running this action describes the curve illustrated below:  --- 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)