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easing
Easing

The Easing module implements common easing functions. This module is used by Animated.timing() to convey physically believable motion in animations.

You can find a visualization of some common easing functions at http://easings.net/

Predefined animations

The Easing module provides several predefined animations through the following methods:

  • back provides a basic animation where the object goes slightly back before moving forward
  • bounce provides a bouncing animation
  • ease provides a basic inertial animation
  • elastic provides a basic spring interaction

Standard functions

Three standard easing functions are provided:

The poly function can be used to implement quartic, quintic, and other higher power functions.

Additional functions

Additional mathematical functions are provided by the following methods:

  • bezier provides a cubic bezier curve
  • circle provides a circular function
  • sin provides a sinusoidal function
  • exp provides an exponential function

The following helpers are used to modify other easing functions.

  • in runs an easing function forwards
  • inOut makes any easing function symmetrical
  • out runs an easing function backwards

Example

import React from "react";
import { Animated, Easing, SectionList, StatusBar, StyleSheet, Text, TouchableOpacity, View } from "react-native";

const App = () => {
  let opacity = new Animated.Value(0);

  const animate = easing => {
    opacity.setValue(0);
    Animated.timing(opacity, {
      toValue: 1,
      duration: 1200,
      easing
    }).start();
  };

  const size = opacity.interpolate({
    inputRange: [0, 1],
    outputRange: [0, 80]
  });

  const animatedStyles = [
    styles.box,
    {
      opacity,
      width: size,
      height: size
    }
  ];

  return (
    <View style={styles.container}>
      <StatusBar hidden={true} />
      <Text style={styles.title}>
        Press rows below to preview the Easing!
      </Text>
      <View style={styles.boxContainer}>
        <Animated.View style={animatedStyles} />
      </View>
      <SectionList
        style={styles.list}
        sections={SECTIONS}
        keyExtractor={(item) => item.title}
        renderItem={({ item }) => (
          <TouchableOpacity
            onPress={() => animate(item.easing)}
            style={styles.listRow}
          >
            <Text>{item.title}</Text>
          </TouchableOpacity>
        )}
        renderSectionHeader={({ section: { title } }) => (
          <Text style={styles.listHeader}>{title}</Text>
        )}
      />
    </View>
  );
};

const SECTIONS = [
  {
    title: "Predefined animations",
    data: [
      { title: "Bounce", easing: Easing.bounce },
      { title: "Ease", easing: Easing.ease },
      { title: "Elastic", easing: Easing.elastic(4) }
    ]
  },
  {
    title: "Standard functions",
    data: [
      { title: "Linear", easing: Easing.linear },
      { title: "Quad", easing: Easing.quad },
      { title: "Cubic", easing: Easing.cubic }
    ]
  },
  {
    title: "Additional functions",
    data: [
      {
        title: "Bezier",
        easing: Easing.bezier(0, 2, 1, -1)
      },
      { title: "Circle", easing: Easing.circle },
      { title: "Sin", easing: Easing.sin },
      { title: "Exp", easing: Easing.exp }
    ]
  },
  {
    title: "Combinations",
    data: [
      {
        title: "In + Bounce",
        easing: Easing.in(Easing.bounce)
      },
      {
        title: "Out + Exp",
        easing: Easing.out(Easing.exp)
      },
      {
        title: "InOut + Elastic",
        easing: Easing.inOut(Easing.elastic(1))
      }
    ]
  }
];

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: "#20232a"
  },
  title: {
    marginTop: 10,
    textAlign: "center",
    color: "#61dafb"
  },
  boxContainer: {
    height: 160,
    alignItems: "center"
  },
  box: {
    marginTop: 32,
    borderRadius: 4,
    backgroundColor: "#61dafb"
  },
  list: {
    backgroundColor: "#fff"
  },
  listHeader: {
    paddingHorizontal: 8,
    paddingVertical: 4,
    backgroundColor: "#f4f4f4",
    color: "#999",
    fontSize: 12,
    textTransform: "uppercase"
  },
  listRow: {
    padding: 8
  }
});

export default App;

Reference

Methods

step0()

static step0(n)

A stepping function, returns 1 for any positive value of n.

step1()

static step1(n)

A stepping function, returns 1 if n is greater than or equal to 1.

linear()

static linear(t)

A linear function, f(t) = t. Position correlates to elapsed time one to one.

http://cubic-bezier.com/#0,0,1,1

ease()

static ease(t)

A basic inertial interaction, similar to an object slowly accelerating to speed.

http://cubic-bezier.com/#.42,0,1,1

quad()

static quad(t)

A quadratic function, f(t) = t * t. Position equals the square of elapsed time.

http://easings.net/#easeInQuad

cubic()

static cubic(t)

A cubic function, f(t) = t * t * t. Position equals the cube of elapsed time.

http://easings.net/#easeInCubic

poly()

static poly(n)

A power function. Position is equal to the Nth power of elapsed time.

n = 4: http://easings.net/#easeInQuart n = 5: http://easings.net/#easeInQuint

sin()

static sin(t)

A sinusoidal function.

http://easings.net/#easeInSine

circle()

static circle(t)

A circular function.

http://easings.net/#easeInCirc

exp()

static exp(t)

An exponential function.

http://easings.net/#easeInExpo

elastic()

static elastic(bounciness)

A basic elastic interaction, similar to a spring oscillating back and forth.

Default bounciness is 1, which overshoots a little bit once. 0 bounciness doesn't overshoot at all, and bounciness of N > 1 will overshoot about N times.

http://easings.net/#easeInElastic

back()

static back(s)

Use with Animated.parallel() to create a basic effect where the object animates back slightly as the animation starts.

bounce()

static bounce(t)

Provides a basic bouncing effect.

http://easings.net/#easeInBounce

bezier()

static bezier(x1, y1, x2, y2)

Provides a cubic bezier curve, equivalent to CSS Transitions' transition-timing-function.

A useful tool to visualize cubic bezier curves can be found at http://cubic-bezier.com/

in()

static in(easing);

Runs an easing function forwards.

out()

static out(easing)

Runs an easing function backwards.

inOut()

static inOut(easing)

Makes any easing function symmetrical. The easing function will run forwards for half of the duration, then backwards for the rest of the duration.