react-native-mock-tmp-build/src/api/Animated/SpringConfig.js

A fully mocked and test-friendly version of react native

/**
 * https://github.com/facebook/react-native/blob/master/Libraries/Animated/src/SpringConfig.js
 */

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

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

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

function fromBouncinessAndSpeed(bounciness, speed) {
  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);
    }
    return b3Friction3(tension);
  }

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

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

module.exports = {
  fromOrigamiTensionAndFriction,
  fromBouncinessAndSpeed,
};