popmotion/lib/animations/utils/find-spring.js

The animator's toolbox

import { warning } from "hey-listen";
import { clamp } from "../../utils/clamp";
var safeMin = 0.001;
export var minDuration = 0.01;
export var maxDuration = 10.0;
export var minDamping = 0.05;
export var maxDamping = 1;
export function findSpring(_a) {
    var _b = _a.duration, duration = _b === void 0 ? 800 : _b, _c = _a.bounce, bounce = _c === void 0 ? 0.25 : _c, _d = _a.velocity, velocity = _d === void 0 ? 0 : _d, _e = _a.mass, mass = _e === void 0 ? 1 : _e;
    var envelope;
    var derivative;
    warning(duration <= maxDuration * 1000, "Spring duration must be 10 seconds or less");
    var dampingRatio = 1 - bounce;
    dampingRatio = clamp(minDamping, maxDamping, dampingRatio);
    duration = clamp(minDuration, maxDuration, duration / 1000);
    if (dampingRatio < 1) {
        envelope = function (undampedFreq) {
            var exponentialDecay = undampedFreq * dampingRatio;
            var delta = exponentialDecay * duration;
            var a = exponentialDecay - velocity;
            var b = calcAngularFreq(undampedFreq, dampingRatio);
            var c = Math.exp(-delta);
            return safeMin - (a / b) * c;
        };
        derivative = function (undampedFreq) {
            var exponentialDecay = undampedFreq * dampingRatio;
            var delta = exponentialDecay * duration;
            var d = delta * velocity + velocity;
            var e = Math.pow(dampingRatio, 2) * Math.pow(undampedFreq, 2) * duration;
            var f = Math.exp(-delta);
            var g = calcAngularFreq(Math.pow(undampedFreq, 2), dampingRatio);
            var factor = -envelope(undampedFreq) + safeMin > 0 ? -1 : 1;
            return (factor * ((d - e) * f)) / g;
        };
    }
    else {
        envelope = function (undampedFreq) {
            var a = Math.exp(-undampedFreq * duration);
            var b = (undampedFreq - velocity) * duration + 1;
            return -safeMin + a * b;
        };
        derivative = function (undampedFreq) {
            var a = Math.exp(-undampedFreq * duration);
            var b = (velocity - undampedFreq) * (duration * duration);
            return a * b;
        };
    }
    var initialGuess = 5 / duration;
    var undampedFreq = approximateRoot(envelope, derivative, initialGuess);
    if (isNaN(undampedFreq)) {
        return {
            stiffness: 100,
            damping: 10,
        };
    }
    else {
        var stiffness = Math.pow(undampedFreq, 2) * mass;
        return {
            stiffness: stiffness,
            damping: dampingRatio * 2 * Math.sqrt(mass * stiffness),
        };
    }
}
var rootIterations = 12;
function approximateRoot(envelope, derivative, initialGuess) {
    var result = initialGuess;
    for (var i = 1; i < rootIterations; i++) {
        result = result - envelope(result) / derivative(result);
    }
    return result;
}
export function calcAngularFreq(undampedFreq, dampingRatio) {
    return undampedFreq * Math.sqrt(1 - dampingRatio * dampingRatio);
}
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