just-animate/lib.es2015/lib/core/interpolate.js

_Making Animation Simple_

import { cssFunction } from 'just-curves';
import { isNumber, isFunction } from '../utils/inspect';
import { memoize } from '../utils/functional';
import { all } from '../utils/lists';
function findEndIndex(ns, n) {
    const ilen = ns.length;
    for (let i = 0; i < ilen; i++) {
        if (ns[i] > n) {
            return i;
        }
    }
    return ilen - 1;
}
const getEasing = memoize(cssFunction);
const getInterpolator = memoize((fn) => memoize(fn));
export function interpolate(l, r, o) {
    return l + (r - l) * o;
}
function fallbackInterpolator(l, r, o) {
    return o < 0.5 ? l : r;
}
export function interpolator(duration, keyframes) {
    const times = keyframes.map(k => k.offset * duration);
    all(keyframes, k => {
        const isSimple = !isFunction(k.interpolate);
        k.simpleFn = isSimple;
        k.interpolate = !isSimple
            ? getInterpolator(k.interpolate)
            : isNumber(k.value)
                ? interpolate
                : fallbackInterpolator;
    });
    return function (timelineOffset) {
        const absTime = duration * timelineOffset;
        const r = findEndIndex(times, absTime);
        const l = r ? r - 1 : 0;
        const rt = times[r];
        const lt = times[l];
        const lk = keyframes[l];
        const time = (absTime - lt) / (rt - lt);
        const progression = lk.easing ? getEasing(lk.easing)(time) : time;
        if (lk.simpleFn) {
            return lk.interpolate(lk.value, keyframes[r].value, progression);
        }
        return lk.interpolate(lk.value, keyframes[r].value)(progression);
    };
}