react-native/Libraries/Animated/SpringConfig.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule SpringConfig
 * @flow
 */

'use strict';

type SpringConfigType = {
  tension: number,
  friction: number,
};

function tensionFromOrigamiValue(oValue) {
  return (oValue - 30) * 3.62 + 194;
}

function frictionFromOrigamiValue(oValue) {
  return (oValue - 8) * 3 + 25;
}

function fromOrigamiTensionAndFriction(
  tension: number,
  friction: number,
): SpringConfigType {
  return {
    tension: tensionFromOrigamiValue(tension),
    friction: frictionFromOrigamiValue(friction)
  };
}

function fromBouncinessAndSpeed(
  bounciness: number,
  speed: number,
): SpringConfigType {
  function normalize(value, startValue, endValue) {
    return (value - startValue) / (endValue - startValue);
  }

  function projectNormal(n, start, end) {
    return start + (n * (end - start));
  }

  function linearInterpolation(t, start, end) {
    return t * end + (1 - t) * start;
  }

  function quadraticOutInterpolation(t, start, end) {
    return linearInterpolation(2 * t - t * t, start, end);
  }

  function b3Friction1(x) {
    return (0.0007 * Math.pow(x, 3)) -
      (0.031 * Math.pow(x, 2)) + 0.64 * x + 1.28;
  }

  function b3Friction2(x) {
    return (0.000044 * Math.pow(x, 3)) -
      (0.006 * Math.pow(x, 2)) + 0.36 * x + 2;
  }

  function b3Friction3(x) {
    return (0.00000045 * Math.pow(x, 3)) -
      (0.000332 * Math.pow(x, 2)) + 0.1078 * x + 5.84;
  }

  function b3Nobounce(tension) {
    if (tension <= 18) {
      return b3Friction1(tension);
    } else if (tension > 18 && tension <= 44) {
      return b3Friction2(tension);
    } else {
      return b3Friction3(tension);
    }
  }

  var b = normalize(bounciness / 1.7, 0, 20);
  b = projectNormal(b, 0, 0.8);
  var s = normalize(speed / 1.7, 0, 20);
  var bouncyTension = projectNormal(s, 0.5, 200);
  var bouncyFriction = quadraticOutInterpolation(
    b,
    b3Nobounce(bouncyTension),
    0.01
  );

  return {
    tension: tensionFromOrigamiValue(bouncyTension),
    friction: frictionFromOrigamiValue(bouncyFriction)
  };
}

module.exports = {
  fromOrigamiTensionAndFriction,
  fromBouncinessAndSpeed,
};