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Curves.decelerate (flutter#7284)
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Port DecelerateInterpolator to Flutter.

Also, hide the Curve subclasses that you can't extend and that have no
statics and are generally not useful.
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@Hixie
Hixie authored Dec 16, 2016
1 parent 6d4191e commit 3e3d219
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128 changes: 85 additions & 43 deletions packages/flutter/lib/src/animation/curves.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -4,12 +4,6 @@

import 'dart:math' as math;

double _evaluateCubic(double a, double b, double m) {
return 3 * a * (1 - m) * (1 - m) * m + 3 * b * (1 - m) * m * m + m * m * m;
}

const double _kCubicErrorBound = 0.001;

/// A mapping of the unit interval to the unit interval.
///
/// A curve must map 0.0 to 0.0 and 1.0 to 1.0.
Expand All @@ -20,9 +14,9 @@ abstract class Curve {
/// const constructors so that they can be used in const expressions.
const Curve();

/// Returns the value of the curve at point [t].
/// Returns the value of the curve at point `t`.
///
/// The value of [t] must be between 0.0 and 1.0, inclusive.
/// The value of `t` must be between 0.0 and 1.0, inclusive.
double transform(double t);

/// Returns a new curve that is the reversed inversion of this one.
Expand All @@ -38,8 +32,8 @@ abstract class Curve {
/// The identity map over the unit interval.
///
/// See [Curves.linear] for an instance of this class.
class Linear extends Curve {
const Linear._();
class _Linear extends Curve {
const _Linear._();

@override
double transform(double t) => t;
Expand Down Expand Up @@ -105,7 +99,7 @@ class Interval extends Curve {

@override
String toString() {
if (curve is! Linear)
if (curve is! _Linear)
return '$runtimeType($begin\u22EF$end)\u27A9$curve';
return '$runtimeType($begin\u22EF$end)';
}
Expand Down Expand Up @@ -176,6 +170,14 @@ class Cubic extends Curve {
/// to the curve at the point (1, 1).
final double d;

static const double _kCubicErrorBound = 0.001;

double _evaluateCubic(double a, double b, double m) {
return 3 * a * (1 - m) * (1 - m) * m +
3 * b * (1 - m) * m * m +
m * m * m;
}

@override
double transform(double t) {
double start = 0.0;
Expand All @@ -198,20 +200,6 @@ class Cubic extends Curve {
}
}

double _bounce(double t) {
if (t < 1.0 / 2.75) {
return 7.5625 * t * t;
} else if (t < 2 / 2.75) {
t -= 1.5 / 2.75;
return 7.5625 * t * t + 0.75;
} else if (t < 2.5 / 2.75) {
t -= 2.25 / 2.75;
return 7.5625 * t * t + 0.9375;
}
t -= 2.625 / 2.75;
return 7.5625 * t * t + 0.984375;
}

/// A curve that is the reversed inversion of its given curve.
///
/// This curve evalutes the given curve in reverse (i.e., from 1.0 to 0.0 as t
Expand All @@ -235,11 +223,48 @@ class FlippedCurve extends Curve {
}
}

/// A curve where the rate of change starts out quickly and then decelerates; an
/// upside-down `f(t) = t²` parabola.
///
/// This is equivalent to the Android `DecelerateInterpolator` class with a unit
/// factor (the default factor).
///
/// See [Curves.decelerate] for an instance of this class.
class _DecelerateCurve extends Curve {
const _DecelerateCurve._();

@override
double transform(double t) {
// Intended to match the behavior of:
// https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/view/animation/DecelerateInterpolator.java
// ...as of December 2016.
t = 1.0 - t;
return 1.0 - t * t;
}
}


// BOUNCE CURVES

double _bounce(double t) {
if (t < 1.0 / 2.75) {
return 7.5625 * t * t;
} else if (t < 2 / 2.75) {
t -= 1.5 / 2.75;
return 7.5625 * t * t + 0.75;
} else if (t < 2.5 / 2.75) {
t -= 2.25 / 2.75;
return 7.5625 * t * t + 0.9375;
}
t -= 2.625 / 2.75;
return 7.5625 * t * t + 0.984375;
}

/// An oscillating curve that grows in magnitude.
///
/// See [Curves.bounceIn] for an instance of this class.
class BounceInCurve extends Curve {
const BounceInCurve._();
class _BounceInCurve extends Curve {
const _BounceInCurve._();

@override
double transform(double t) {
Expand All @@ -250,8 +275,8 @@ class BounceInCurve extends Curve {
/// An oscillating curve that shrink in magnitude.
///
/// See [Curves.bounceOut] for an instance of this class.
class BounceOutCurve extends Curve {
const BounceOutCurve._();
class _BounceOutCurve extends Curve {
const _BounceOutCurve._();

@override
double transform(double t) {
Expand All @@ -262,8 +287,8 @@ class BounceOutCurve extends Curve {
/// An oscillating curve that first grows and then shrink in magnitude.
///
/// See [Curves.bounceInOut] for an instance of this class.
class BounceInOutCurve extends Curve {
const BounceInOutCurve._();
class _BounceInOutCurve extends Curve {
const _BounceInOutCurve._();

@override
double transform(double t) {
Expand All @@ -274,6 +299,9 @@ class BounceInOutCurve extends Curve {
}
}


// ELASTIC CURVES

/// An oscillating curve that grows in magnitude while overshooting its bounds.
class ElasticInCurve extends Curve {
/// Creates an elastic-in curve.
Expand Down Expand Up @@ -345,12 +373,26 @@ class ElasticInOutCurve extends Curve {
}
}


// PREDEFINED CURVES

/// A collection of common animation curves.
class Curves {
Curves._();

/// A linear animation curve
static const Linear linear = const Linear._();
/// A linear animation curve.
///
/// This is the identity map over the unit interval: its [Curve.transform]
/// method returns its input unmodified. This is useful as a default curve for
/// cases where a [Curve] is required but no actual curve is desired.
static const Curve linear = const _Linear._();

/// A curve where the rate of change starts out quickly and then decelerates; an
/// upside-down `f(t) = t²` parabola.
///
/// This is equivalent to the Android `DecelerateInterpolator` class with a unit
/// factor (the default factor).
static const Curve decelerate = const _DecelerateCurve._();

/// A cubic animation curve that speeds up quickly and ends slowly.
static const Cubic ease = const Cubic(0.25, 0.1, 0.25, 1.0);
Expand All @@ -364,14 +406,21 @@ class Curves {
/// A cubic animation curve that starts slowly, speeds up, and then and ends slowly.
static const Cubic easeInOut = const Cubic(0.42, 0.0, 0.58, 1.0);

/// A curve that starts quickly and eases into its final position.
///
/// Over the course of the animation, the object spends more time near its
/// final destination. As a result, the user isn’t left waiting for the
/// animation to finish, and the negative effects of motion are minimized.
static const Cubic fastOutSlowIn = const Cubic(0.4, 0.0, 0.2, 1.0);

/// An oscillating curve that grows in magnitude.
static const BounceInCurve bounceIn = const BounceInCurve._();
static const Curve bounceIn = const _BounceInCurve._();

/// An oscillating curve that first grows and then shrink in magnitude.
static const BounceOutCurve bounceOut = const BounceOutCurve._();
static const Curve bounceOut = const _BounceOutCurve._();

/// An oscillating curve that first grows and then shrink in magnitude.
static const BounceInOutCurve bounceInOut = const BounceInOutCurve._();
static const Curve bounceInOut = const _BounceInOutCurve._();

/// An oscillating curve that grows in magnitude while overshootings its bounds.
static const ElasticInCurve elasticIn = const ElasticInCurve();
Expand All @@ -381,11 +430,4 @@ class Curves {

/// An oscillating curve that grows and then shrinks in magnitude while overshootings its bounds.
static const ElasticInOutCurve elasticInOut = const ElasticInOutCurve();

/// A curve that starts quickly and eases into its final position.
///
/// Over the course of the animation, the object spends more time near its
/// final destination. As a result, the user isn’t left waiting for the
/// animation to finish, and the negative effects of motion are minimized.
static const Curve fastOutSlowIn = const Cubic(0.4, 0.0, 0.2, 1.0);
}
12 changes: 12 additions & 0 deletions packages/flutter/test/animation/curves_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -91,4 +91,16 @@ void main() {
expect(bounds[0], lessThan(0.0));
expect(bounds[1], greaterThan(1.0));
});

test('Decelerate does so', () {
expect(Curves.decelerate, hasOneLineDescription);

List<double> bounds = estimateBounds(Curves.decelerate);
expect(bounds[0], greaterThanOrEqualTo(0.0));
expect(bounds[1], lessThanOrEqualTo(1.0));

double d1 = Curves.decelerate.transform(0.2) - Curves.decelerate.transform(0.0);
double d2 = Curves.decelerate.transform(1.0) - Curves.decelerate.transform(0.8);
expect(d2, lessThan(d1));
});
}

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