@google/model-viewer
Version:
Easily display interactive 3D models on the web and in AR!
69 lines • 3.07 kB
JavaScript
/* @license
* Copyright 2020 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.
*/
export const SETTLING_TIME = 10000; // plenty long enough
const MIN_DECAY_MILLISECONDS = 0.001;
export const DECAY_MILLISECONDS = 50;
/**
* The Damper class is a generic second-order critically damped system that does
* one linear step of the desired length of time. The only parameter is
* DECAY_MILLISECONDS. This common parameter makes all states converge at the
* same rate regardless of scale. xNormalization is a number to provide the
* rough scale of x, such that NIL_SPEED clamping also happens at roughly the
* same convergence for all states.
*/
export class Damper {
constructor(decayMilliseconds = DECAY_MILLISECONDS) {
this.velocity = 0;
this.naturalFrequency = 0;
this.setDecayTime(decayMilliseconds);
}
setDecayTime(decayMilliseconds) {
this.naturalFrequency =
1 / Math.max(MIN_DECAY_MILLISECONDS, decayMilliseconds);
}
update(x, xGoal, timeStepMilliseconds, xNormalization) {
const nilSpeed = 0.0002 * this.naturalFrequency;
if (x == null || xNormalization === 0) {
return xGoal;
}
if (x === xGoal && this.velocity === 0) {
return xGoal;
}
if (timeStepMilliseconds < 0) {
return x;
}
// Exact solution to a critically damped second-order system, where:
// acceleration = this.naturalFrequency * this.naturalFrequency * (xGoal
// - x) - 2 * this.naturalFrequency * this.velocity;
const deltaX = (x - xGoal);
const intermediateVelocity = this.velocity + this.naturalFrequency * deltaX;
const intermediateX = deltaX + timeStepMilliseconds * intermediateVelocity;
const decay = Math.exp(-this.naturalFrequency * timeStepMilliseconds);
const newVelocity = (intermediateVelocity - this.naturalFrequency * intermediateX) * decay;
const acceleration = -this.naturalFrequency * (newVelocity + intermediateVelocity * decay);
if (Math.abs(newVelocity) < nilSpeed * Math.abs(xNormalization) &&
acceleration * deltaX >= 0) {
// This ensures the controls settle and stop calling this function instead
// of asymptotically approaching their goal.
this.velocity = 0;
return xGoal;
}
else {
this.velocity = newVelocity;
return xGoal + intermediateX * decay;
}
}
}
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