Foil

Wrap a widget with Foil, providing a rainbow shimmer
that twinkles as the accelerometer moves.

Consider holographic Pokémon trading cards, some credit cards,
or an oil slick on the road.

📚 Table of Contents

• Getting Started
  • Accelerometer
  • Transitioning
• Advanced Usage
  • Rolls
  • Crinkles
  • TransformGradient
• Extra Goodies
  • Steps
  • GradientUtils Extensions
  • Foils
• Reference
  • 📖 API Documentation
  • Foil Demo: 👷‍♂️ source code, 📲 built APK
  • 🛣️ Roadmap
  • 🐞 Bugs

Getting Started

Wrap a widget by providing it as Foil.child.

Use any gradient of choice and determine the blendMode to mask the gradient
onto the child in different ways. Default is BlendMode.srcATop which will
reveal the child through the gradient if the gradient has opacity or if
Foil.opacity is provided a non-1.0 value.

• Use BlendMode.srcIn to paint only the gradient and use the child as a mask.

Flag isUnwrapped toggles this Foil's invisibility. Default is false.
When this value is changed, the gradient will smoothly animate to a disabled
state, leaving only the child behind.

class Example extends StatelessWidget {
  const Example({Key? key}): super(key: key);

  @override
  Widget build(BuildContext context) => FittedBox(
    child: Foil(
      child: const Text(
        'FOIL',
        style: TextStyle(fontWeight: FontWeight.w900)
      ),
    ),
  );
}

Quickstart

Plop an instance of this const Example() in a running ListView you've got open in a code editor.
Run terminal command flutter pub add foil.
import 'package:foil/foil.dart'

Accelerometer

This trading card is wrapped in two Foil widgets offering different gradients!
Further widget transformation provided by package:xl.

Disable this Foil's reaction to accelerometer sensor motion by
useSensor: false. Default is true.

• In this case, you may want to employ a Roll with Crinkles.

Influence the intensity of this Foil's reaction to accelerometer motion
by providing a speed and custom Scalar property Foil.scalar.

• Default is Scalar.identity which has both a horizontal and vertical
  multiplier of +1.0.

Transitioning

Control how rapidly this Foil transforms its gradient with Foil.speed
and define the animation curve. Defaults are 150ms and Curves.ease.

	Furthermore, provide Foil.duration to dictate how long intrinsic animations of gradient will take. Foil.duration is also used if isUnwrapped is made true as the duration over which Foil.gradient will lerp to an appropriately-Typed transparent gradient for tweening. There is hard-coded recognition for linear, radial, and sweep gradients, as well as the additional Steps variants this package provides. Falls back to a transparent LinearGradient if Type cannot be matched. Override with Foil.unwrappedGradient. Click images to view full size.

Upon completion of any tween to a new gradient, this Foil will call onEnd, an optional void callback.

Advanced Usage

Rolls

Wrap any Foil (or many of them!) in a Roll higher in the widget tree
to provide some inherited properties.

A gradient provided by an ancestral Roll may be used by as a Foil.gradient
if one is not explicitly perscribed in the Foil.

• If neither an ancestral Roll nor a Foil dictates its own gradient, then the default is Foils.linearLooping.
• A descendent that provides its own Foil.gradient will override the Roll.gradient.

One day a Roll will also provide the option to "cut" any descendent Foil from a single shared gradient sheet that covers a space the size of the Roll.

Rolls can also serve to provide animation properties to a descendent Foil,
regardless of whether its serving its gradient.

Crinkles

These animations are in addition to any accelerometer sensors data
already animating the Foil unless Foil.useSensors: false.

	The Roll.crinkle parameter defaults to Crinkle.smooth which is not animated (although each Roll has its own AnimationController for toggling purposes). A Crinkle dictates speed, intensity, and directionality of animation. Click image to view full size.

• Crinkle.smooth is a non-animated preset
• Crinkle.crawling is a very slow moving preset
• Crinkle.twinkling is a little bit faster
• Crinkle.vivacious is highly-animated
• Build your own or opt to Crinkle.copyWith a preset
  • isAnimated, shouldReverse flags
  • Use period to determine the animation loop Duration
  • The scalar property can be used to invert, scale, or negate axes
    (this is a Scalar object like a Foil uses to scale its sensors data)

TransformGradient

This is the definition of a function that takes in a scaled double x and double y
and returns a GradientTransform object. That object is used when a Foil's
gradient shader is drawn by calling its transform() method.

To provide a custom transformation as Crinkle.transform, extend that class
and override transform(), returning some Matrix4, such as the default
for this package:

class TranslateGradient extends GradientTransform {
  /// The default [TransformGradient] for `Foil`.
  /// This class's [transform] method considers [TextDirection] and
  /// will consider positive values as translation to the right if `ltr`
  /// and translate left for positive values if `rtl`.
  const TranslateGradient({required this.percentX, required this.percentY});
  final double percentX, percentY;

  /// Returning `null` here is equivalent to returning `Matrix4.identity`.
  @override
  Matrix4? transform(Rect bounds, {TextDirection? textDirection}) =>
    Matrix4.translationValues(
      (textDirection == TextDirection.rtl ? -1.0 : 1.0) * bounds.width * percentX,
      bounds.height * percentY,
      0.0,
    );
}

Extra Goodies

This package also comes with some other offerings.
Some expand on Gradient functionality, and others make them simpler to use.

Up first is named Foil.sheet which functions like a self-contained
Foil + AnimatedContainer. Stylized by a Sheet which simply wraps
parameters for the AnimatedContainer.

Steps

The basic premise of a gradient is to gradate between colors.
Consider new Steps to be extensions of Gradients, one each for linear, radial, and sweep,
where the colors do not gradate but instead hard-transition. Like steps!
RadialSteps are great for making rainbows.

| SweepSteps | RadialSteps | LinearSteps |

GradientUtils Extensions

Along with the three new variety of Gradient, this package
provides 📋 copyWith() methods for each existing Flutter type.

final copy = RadialGradient(
  colors: [. . .],
  stops: [. . .],
  center: const Alignment(0, 0),
).copyWith(center: const Alignment(-2, -2));

Even the superclass Gradient may be copied, provided this is a standard linear, radial, or sweep gradient, or one of the three new steps gradients (falls back to a standard linear gradient). Provides every potential copyable parameter from the varieties. Most useful in a scenario where a common parameter like colors or transform is to be applied to some arbitrary Gradient.

This makes it a cinch to pick out pre-rolled Foils
yet tweak them for specific scenarios--such as changing
start and end points while maintaining the list of colors.

What are Foils?

Foils

Finally, this package is bundled with a selection of pre-defined gradients.
One such pre-rolled Foils.oilslick has opacity within each Color.

• But consider that the Foil constructor accepts an overriding
  opacity parameter for semi-transparent appearance even without
  Gradient.colors that have opacity.

	The default gradient for this package is Foils.linearLooping, a nice 'n' simple LinearGradient. Reverse the order of colors with Foils.linearReversed. To only cycle through the rainbow once see Foils.linearRainbow. Click image to view full size.

Find other options like Foils.gymClassParachute and Foils.sitAndSpin,
then tweak them to your liking with the 📋 Gradient.copyWith() methods.

There is even a literal rainbow decal gradient made with the new RadialSteps type. Click image to view full size.

Reference

📖 API Documentation

Foil Demo: 👷‍♂️ source code, 📲 built APK

🛣️ Roadmap

0. Make available a Roll of Foil feature such that a developer could
   deploy a single gradient sheet in a region and mask that single gradient to any
   child Foil widgets.
   • Rolls are implemented now, but only offer to pass a Gradient to
     descendent Foils--not to mask them from the same gradient.
1. If this package's Gradient support expands further, much of that functionality could be forked to an independent package.
2. Custom GradientTransforms will be investigated, for example: to deform Foils.oilslick.

🐞 Bugs

0. Potential optimizations for GradientTweening within lerp(), especially with the new Steps style gradients.
1. Because this package's copyWith() method for the superclass Gradient is used when applying Crinkle transformation, the returned gradient is limited by the hard-coded return types of the copyWith method; that is to say: the three Flutter Gradients and the three Steps gradients added by this package.
   • If a bespoke Gradient type is used for some Foil that is wrapped in a Roll whose Crinkle provides animation, that gradient will become a LinearGradient with the appropriate colors at least.
   • In this scenario, until this bug is patched, consider transforming the gradient prior to providing it to your Crinkle-animated Foil in order to maintain the bespoke Gradient.

Libraries

foil

Wrap a widget with Foil, providing a rainbow shimmer that twinkles as the accelerometer moves as well as tons of additional neat gradient features.