---
title: "init(from:by:timing:isAdditive:)"
framework: realitykit
role: symbol
role_heading: Initializer
path: "realitykit/fromtobyaction/init(from:by:timing:isadditive:)"
---

# init(from:by:timing:isAdditive:)

Creates a new action that interpolates towards a specified value, which is relative to the starting value.

## Declaration

```swift
init(from: Value? = nil, by: Value, timing: AnimationTimingFunction = .linear, isAdditive: Bool = false)
```

## Parameters

- `from`: Value set at the start of the animation, or nil to use the default source.
- `by`: Value relative to the initial value to determine the final value.
- `timing`: Controls the progress of the animation.
- `isAdditive`: Specifies whether you can additively blend the output from the action’s animation.

## Discussion

Discussion from → from + by or defaultSource → defaultSource + by