planck-js/lib/common/Sweep.js

2D JavaScript physics engine for cross-platform HTML5 game development

/*
 * Planck.js
 * The MIT License
 * Copyright (c) 2021 Erin Catto, Ali Shakiba
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

var _DEBUG = typeof DEBUG === 'undefined' ? false : DEBUG;
var _ASSERT = typeof ASSERT === 'undefined' ? false : ASSERT;

module.exports = Sweep;

var common = require('../util/common');
var Math = require('./Math');
var Vec2 = require('./Vec2');
var Rot = require('./Rot');
var Transform = require('./Transform');

/**
 * This describes the motion of a body/shape for TOI computation. Shapes are
 * defined with respect to the body origin, which may not coincide with the
 * center of mass. However, to support dynamics we must interpolate the center
 * of mass position.
 * 
 * @prop {Vec2} localCenter Local center of mass position
 * @prop {Vec2} c World center position
 * @prop {float} a World angle
 * @prop {float} alpha0 Fraction of the current time step in the range [0,1], c0
 *       and a0 are c and a at alpha0.
 */
function Sweep(c, a) {
  _ASSERT && common.assert(typeof c === 'undefined');
  _ASSERT && common.assert(typeof a === 'undefined');
  this.localCenter = Vec2.zero();
  this.c = Vec2.zero();
  this.a = 0;
  this.alpha0 = 0;
  this.c0 = Vec2.zero();
  this.a0 = 0;
}

Sweep.prototype.setTransform = function(xf) {
  var c = Transform.mulVec2(xf, this.localCenter);
  this.c.set(c);
  this.c0.set(c);

  this.a = xf.q.getAngle();
  this.a0 = xf.q.getAngle();
};

Sweep.prototype.setLocalCenter = function(localCenter, xf) {
  this.localCenter.set(localCenter);

  var c = Transform.mulVec2(xf, this.localCenter);
  this.c.set(c);
  this.c0.set(c);
};

/**
 * Get the interpolated transform at a specific time.
 * 
 * @param xf
 * @param beta A factor in [0,1], where 0 indicates alpha0
 */
Sweep.prototype.getTransform = function(xf, beta) {
  beta = typeof beta === 'undefined' ? 0 : beta;
  xf.q.setAngle((1.0 - beta) * this.a0 + beta * this.a);
  xf.p.setCombine((1.0 - beta), this.c0, beta, this.c);

  // shift to origin
  xf.p.sub(Rot.mulVec2(xf.q, this.localCenter));
};

/**
 * Advance the sweep forward, yielding a new initial state.
 * 
 * @param {float} alpha The new initial time
 */
Sweep.prototype.advance = function(alpha) {
  _ASSERT && common.assert(this.alpha0 < 1.0);
  var beta = (alpha - this.alpha0) / (1.0 - this.alpha0);
  this.c0.setCombine(beta, this.c, 1 - beta, this.c0);
  this.a0 = beta * this.a + (1 - beta) * this.a0;
  this.alpha0 = alpha;
};

Sweep.prototype.forward = function() {
  this.a0 = this.a;
  this.c0.set(this.c);
};

/**
 * normalize the angles in radians to be between -pi and pi.
 */
Sweep.prototype.normalize = function() {
  var a0 = Math.mod(this.a0, -Math.PI, +Math.PI);
  this.a -= this.a0 - a0;
  this.a0 = a0;
};

Sweep.prototype.clone = function() {
  var clone = new Sweep();
  clone.localCenter.set(this.localCenter);
  clone.alpha0 = this.alpha0;
  clone.a0 = this.a0;
  clone.a = this.a;
  clone.c0.set(this.c0);
  clone.c.set(this.c);
  return clone;
};

Sweep.prototype.set = function(that) {
  this.localCenter.set(that.localCenter);
  this.alpha0 = that.alpha0;
  this.a0 = that.a0;
  this.a = that.a;
  this.c0.set(that.c0);
  this.c.set(that.c);
};