Interpolate

Interpolate is a powerful Swift interpolation framework for creating interactive gesture-driven animations.

Usage

The idea of Interpolate is - all animation is the interpolation of values over time.

To use Interpolate:

Import Interpolate at the top of your Swift file.

import Interpolate

Create an Interpolate object with a from value, a to value and an apply closure that applies the interpolation's result to the target object.

let colorChange = Interpolate(from: UIColor.whiteColor(),
to: UIColor.redColor(),
apply: { [weak self] (result) in
    if let color = result as? UIColor {
      self?.view.backgroundColor = color
    }
})

Next, you will need to define a way to translate your chosen gesture's progress to a percentage value (i.e. a CGFloat between 0.0 and 1.0).

For a gesture recognizer or delegate that reports every step of its progress (e.g. UIPanGestureRecognizer or a ScrollViewDidScroll) you can just apply the percentage directly to the Interpolate object:

@IBAction func handlePan(recognizer: UIPanGestureRecognizer) {
    let translation = recognizer.translationInView(self.view)
    let translatedCenterY = view.center.y + translation.y
    let progress = translatedCenterY / self.view.bounds.size.height
    colorChange.progress = progress
}

For other types of gesture recognizers that only report a beginning and an end (e.g. a UILongPressGestureRecognizer), you can animate directly to a target progress value with a given duration. For example:

@IBAction func handleLongPress(recognizer: UILongPressGestureRecognizer) {
    switch recognizer.state {
        case .Began:
            colorChange.animate(1.0, duration: 0.3)
        case .Cancelled, .Ended, .Failed:
            colorChange.animate(0.0, duration: 0.3)
        default: break
    }
}

To stop an animation:

colorChange.stopAnimation()

When you are done with the interpolation altogether:

colorChange.invalidate()

Voila!

What can I interpolate?

Interpolate currently supports the interpolation of:

CGPoint
CGRect
CGSize
Double
CGFloat
Int
NSNumber
UIColor
CGAffineTransform
CATransform3D

More types will be added over time.

Advanced usage

Interpolate is not just for dull linear interpolations.

For smoother animations, consider using any of the following functions: EaseIn, EaseOut, EaseInOut and Spring.

// Spring interpolation
let shadowPosition = Interpolate(from: -shadowView.frame.size.width,
to: (self.view.bounds.size.width - shadowView.frame.size.width)/2,
function: SpringInterpolation(damping: 30.0, velocity: 0.0, mass: 1.0, stiffness: 100.0),
apply: { [weak self] (result) in
  if let originX = result as? CGFloat {
      self?.shadowView.frame.origin.x = originX
  }
})

// Ease out interpolation
let groundPosition = Interpolate(from: CGPointMake(0, self.view.bounds.size.height),
to: CGPointMake(0, self.view.bounds.size.height - 150),
function: BasicInterpolation.EaseOut,
apply: { [weak self] (result) in
    if let origin = result as? CGPoint {
        self?.groundView.frame.origin = origin
    }
})

In fact, you can easily create and use your own interpolation function - all you need is an object that conforms to the InterpolationFunction protocol.

Setting up with CocoaPods

source 'https://github.com/CocoaPods/Specs.git'
pod 'Interpolate', '~> 0.1'

Setting up with Carthage

Carthage is a decentralized dependency manager that automates the process of adding frameworks to your Cocoa application.

You can install Carthage with Homebrew using the following command:

$ brew update
$ brew install carthage

To integrate Interpolate into your Xcode project using Carthage, specify it in your Cartfile:

github "marmelroy/Interpolate"