SwiftUI Animatable Gradients

A collection of SwiftUI View Modifiers for creating animated color gradients.

🔗Clone or download this repo and play around with the Demo app.
🔗Download this Swift Playgrounds Book to play around with some of the library's underlying code in the Swift Playgrounds App.

Features

Linear Gradients
Radial Gradients
Angular Gradients
Direct ViewModifier Usage on Shapes
Direct ViewModifier Usage on Views -- when a custom Shape is defined.
Interpolate between as many start and end colors as you want.

Requirements

iOS 13.0+
iPadOS 13.0+
tvOS 13.0+
Xcode 11.3+ (for developing)

Installation

AnimatableGradients can be used through the Swift Package Manager. You can add it as a dependency in your Package.swift file:

let package = Package(
    //...
    dependencies: [
        .package(url: "https://github.com/CypherPoet/AnimatableGradients", from: "0.1.1"),
    ],
    //...
)

Then simply import AnimatableGradients wherever you’d like to use it.

Usage

The view modifiers exposed by AnimatableGradients all conform to its AnimatableGradientModifier protocol. (You can view the implementation here.)

AnimatableGradientModifier Protocol

protocol AnimatableGradientModifier: AnimatableModifier {
    associatedtype BaseShape: Shape
    associatedtype GradientShapeStyle: ShapeStyle

    var baseShape: BaseShape { get }
    var startColors: [UIColor] { get }
    var endColors: [UIColor] { get }

    var completionPercentage: CGFloat { get set }

    func gradientFill(in geometry: GeometryProxy) -> GradientShapeStyle
}

To use these modifiers, AnimatableGradients provides the following extensions on Views and Shapes:

animatableLinearGradient
animatableRadialGradient
animatableAngularGradient

(More detailed explanations of each can be found below.)

🔑 In order to achieve animation, your containing views will need to provide the aforementioned modifiers with a bound CGFloat state value that ranges between 0.0 and 1.0.

@State private var animationCompletion: CGFloat = 0.0

This is the "animation completion" percentage that each AnimatableGradientModifier will use to generate interpolated color values during each rendered frame.

Additionally, the same containing views will need to animate the change of the animation completion. A common pattern consists of animating the value repeatedly from the containing view's onAppear modifier to create a continuous animation effect:

.onAppear {
    withAnimation(
        Animation.easeInOut(duration: 1.0).repeatForever(autoreverses: true)
    ) {
        self.animationCompletion = 1.0
    }
}

Taken together, a minimal functional example could look like this:

struct ContentView {
    @State private var animationCompletion: CGFloat = 0.0

    var body: some View {
        RoundedRectangle(cornerRadius: 24)
            .animatableLinearGradient(
                startColors: [.red, .blue],
                endColors: [.green, .yellow],
                completionPercentage: animationCompletion
            )
            .onAppear {
                withAnimation(
                    Animation.easeInOut(duration: 1.0).repeatForever(autoreverses: true)
                ) {
                    self.animationCompletion = 1.0
                }
            }
    }
}

But now for some more detail...

Animatable Linear Gradients

Usage on Shapes

extension Shape {

    public func animatableLinearGradient (
        startColors: [UIColor],
        endColors: [UIColor],
        startPoint: UnitPoint = .topLeading,
        endPoint: UnitPoint = .bottomTrailing,
        completionPercentage: CGFloat
    ) -> some View {
      ...
    }
}

What you're using 👆

RoundedRectangle(cornerRadius: 24)
    .animatableLinearGradient(
        startColors: [.systemPurple, .systemBlue, .systemGreen, .white],
        endColors: [.systemGray, .systemPink, .systemOrange, .systemRed],
        completionPercentage: animationCompletion
    )

How you might use it 👆

Usage on Views

extension View {

    public func animatableLinearGradient<BaseShape: Shape>(
        baseShape: BaseShape,
        startColors: [UIColor],
        endColors: [UIColor],
        startPoint: UnitPoint = .topLeading,
        endPoint: UnitPoint = .bottomTrailing,
        completionPercentage: CGFloat
    ) -> some View {
      ...
    }
}

What you're using 👆

Color.clear
    .animatableLinearGradient(
            baseShape: RoundedRectangle(cornerRadius: 24),
            startColors: [.systemPurple, .systemBlue, .systemGreen, .white],
            endColors: [.systemGray, .systemPink, .systemOrange, .systemRed],
            completionPercentage: animationCompletion
    )

How you might use it 👆

📸 Example

Animatable Radial Gradients

Usage on Shapes

extension Shape {

   public func animatableRadialGradient (
        startColors: [UIColor],
        endColors: [UIColor],
        centerPoint: UnitPoint = .center,
        startRadius: CGFloat? = nil,
        endRadius: CGFloat? = nil,
        completionPercentage: CGFloat
    ) -> some View {
        ...
    }
}

What you're using 👆

RoundedRectangle(cornerRadius: 24)
    .animatableRadialGradient(
        startColors: [.systemPurple, .systemBlue, .systemGreen, .white],
        endColors: [.systemGray, .systemPink, .systemOrange, .black],
        completionPercentage: animationCompletion
    )

How you might use it 👆

Usage on Views

extension View {

    public func animatableRadialGradient<BaseShape: Shape>(
        baseShape: BaseShape,
        startColors: [UIColor],
        endColors: [UIColor],
        centerPoint: UnitPoint = .center,
        startRadius: CGFloat? = nil,
        endRadius: CGFloat? = nil,
        completionPercentage: CGFloat
    ) -> some View {
        ...
    }
}

What you're using 👆

Color.clear
    .animatableRadialGradient(
        baseShape: RoundedRectangle(cornerRadius: 24),
        startColors: [.systemPurple, .systemBlue, .systemGreen, .white],
        endColors: [.systemGray, .systemPink, .systemOrange, .black],
        completionPercentage: animationCompletion
    )

How you might use it 👆

📸 Example

Animatable Angular Gradients

Usage on Shapes

extension Shape {

    /// - Parameters:
    ///   - fullSpanStartAngle: Setting this property will cause the gradient to being at
    ///         the specified offset, and then span the entire circumference. (Default: `nil`)
    public func animatableAngularGradient (
        startColors: [UIColor],
        endColors: [UIColor],
        centerPoint: UnitPoint = .center,
        fullSpanStartAngle: Angle,
        completionPercentage: CGFloat
    ) -> some View {
        ...
    }


    public func animatableAngularGradient (
        startColors: [UIColor],
        endColors: [UIColor],
        centerPoint: UnitPoint = .center,
        startAngle: Angle = .zero,
        endAngle: Angle = .radians(2 * .pi),
        completionPercentage: CGFloat
    ) -> some View {
        ...
    }
}

What you're using 👆

RoundedRectangle(cornerRadius: 24)
    .animatableAngularGradient(
        startColors: [.systemPurple, .systemBlue, .systemGreen, .white],
        endColors: [.systemGray, .systemPink, .systemOrange, .systemRed],
        completionPercentage: animationCompletion
    )

How you might use it 👆

Usage on Views

extension View {

    /// - Parameters:
    ///   - fullSpanStartAngle: Setting this property will cause the gradient to being at
    ///         the specified offset, and then span the entire circumference. (Default: `nil`)
    public func animatableAngularGradient<BaseShape: Shape>(
        baseShape: BaseShape,
        startColors: [UIColor],
        endColors: [UIColor],
        centerPoint: UnitPoint = .center,
        fullSpanStartAngle: Angle,
        completionPercentage: CGFloat
    ) -> some View {
        ...
    }


    public func animatableAngularGradient<BaseShape: Shape>(
        baseShape: BaseShape,
        startColors: [UIColor],
        endColors: [UIColor],
        centerPoint: UnitPoint = .center,
        startAngle: Angle = .zero,
        endAngle: Angle = .radians(2 * .pi),
        completionPercentage: CGFloat
    ) -> some View {
        ...
    }
}

What you're using 👆

Color.clear
    .animatableAngularGradient(
        baseShape: RoundedRectangle(cornerRadius: 24),
        startColors: [.systemPurple, .systemBlue, .systemGreen, .white],
        endColors: [.systemGray, .systemPink, .systemOrange, .systemRed],
        completionPercentage: animationCompletion
    )

How you might use it 👆

📸 Example

⚠️ Edge Cases

If you pass a completionPercentage value less than 0, or greater than 1, it will automatically be clamped to the closer endpoint.
Behind the scenes, the startColors and endColors arrays get zipped before the interpolated colors are computed. This means that if their sizes are different, the larger array will be trimmed down to the size of the smaller array, and the excess colors in the larger array won't be used.
- As such, if either or both of the startColors and endColors arrays are empty, the gradient will have no colors passed to it and it will appear completely clear.

Contributing

Contributions to AnimatableGradients are most welcome. Check out some of the issue templates for more info.

Roadmap

Mac Catalyst Support (?)
watchOS Support (?)

License

AnimatableGradients is available under the MIT license. See the LICENSE file for more info.