@google/model-viewer/lib/utilities/animation.js

Easily display interactive 3D models on the web and in AR!

/* @license
 * Copyright 2019 Google LLC. All Rights Reserved.
 * Licensed under the Apache License, Version 2.0 (the 'License');
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an 'AS IS' BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import { clamp } from '../utilities.js';
// Adapted from https://gist.github.com/gre/1650294
export const easeInOutQuad = (t) => t < .5 ? 2 * t * t : -1 + (4 - 2 * t) * t;
/**
 * Creates a TimingFunction that uses a given ease to interpolate between
 * two configured number values.
 */
export const interpolate = (start, end, ease = easeInOutQuad) => (time) => start + (end - start) * ease(time);
/**
 * Creates a TimingFunction that interpolates through a weighted list
 * of other TimingFunctions ("tracks"). Tracks are interpolated in order, and
 * allocated a percentage of the total time based on their relative weight.
 */
export const sequence = (tracks, weights) => {
    const cumulativeSum = ((sum) => (value) => sum += value);
    const times = weights.map(cumulativeSum(0));
    return (time) => {
        time = clamp(time, 0, 1);
        time *= times[times.length - 1];
        const i = times.findIndex((val) => val >= time);
        const start = i < 1 ? 0 : times[i - 1];
        const end = times[i];
        return tracks[i]((time - start) / (end - start));
    };
};
/**
 * Creates a "timeline" TimingFunction out of an initial value and a series of
 * Keyframes. The timeline function accepts value from 0-1 and returns the
 * current value based on keyframe interpolation across the total number of
 * frames. Frames are only used to indicate the relative length of each keyframe
 * transition, so interpolated values will be computed for fractional frames.
 */
export const timeline = (path) => {
    const tracks = [];
    const weights = [];
    let lastValue = path.initialValue;
    for (let i = 0; i < path.keyframes.length; ++i) {
        const keyframe = path.keyframes[i];
        const { value, frames } = keyframe;
        const ease = keyframe.ease || easeInOutQuad;
        const track = interpolate(lastValue, value, ease);
        tracks.push(track);
        weights.push(frames);
        lastValue = value;
    }
    return sequence(tracks, weights);
};
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