planck-js/lib/shape/CircleShape.js

2D physics engine for JavaScript/HTML5 game development

/*
 * Copyright (c) 2016      Ali Shakiba http://shakiba.me/planck.js
 * Copyright (c) 2006-2011 Erin Catto  http://www.box2d.org
 *
 * This software is provided 'as-is', without any express or implied
 * warranty.  In no event will the authors be held liable for any damages
 * arising from the use of this software.
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 * 1. The origin of this software must not be misrepresented; you must not
 * claim that you wrote the original software. If you use this software
 * in a product, an acknowledgment in the product documentation would be
 * appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 * misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 */

module.exports = CircleShape;

var create = require('../util/create');
var options = require('../util/options');
var Settings = require('../Settings');
var Shape = require('../Shape');
var Math = require('../common/Math');
var Transform = require('../common/Transform');
var Rot = require('../common/Rot');
var Vec2 = require('../common/Vec2');
var AABB = require('../collision/AABB');

CircleShape._super = Shape;
CircleShape.prototype = create(CircleShape._super.prototype);

CircleShape.TYPE = 'circle';

function CircleShape(p, r) {
  if (!(this instanceof CircleShape)) {
    return new CircleShape(p, r);
  }

  CircleShape._super.call(this);

  this.m_type = CircleShape.TYPE;
  this.m_p = Vec2();
  this.m_radius = 1;

  if (typeof p === 'object' && Vec2.IsValid(p)) {
    this.m_p.Set(p);

  } else if (typeof p === 'number') {
    this.m_radius = p;

  } else if (typeof r === 'number') {
    this.m_radius = r;
  }
}

CircleShape.prototype.GetRadius = function() {
  return this.m_radius;
}

CircleShape.prototype.SetRadius = function(r) {
  this.m_radius = r;
  return this;
}

CircleShape.prototype.GetCenter = function() {
  return this.m_p;
}

CircleShape.prototype.SetCenter = function(p) {
  this.m_p.Set(p);
  return this;
}

CircleShape.prototype.GetSupportVertex = function(d) {
  return this.m_p;
}

CircleShape.prototype.GetVertex = function(index) {
  Assert(index == 0);
  return this.m_p;
}

CircleShape.prototype.GetVertexCount = function(index) {
  return 1;
}

CircleShape.prototype.Clone = function() {
  var clone = new CircleShape();
  clone.m_type = this.m_type;
  clone.m_radius = this.m_radius;
  clone.m_p = this.m_p.Clone();
  return clone;
}

CircleShape.prototype.GetChildCount = function() {
  return 1;
}

CircleShape.prototype.TestPoint = function(xf, p) {
  var center = Vec2.Add(xf.p, Rot.Mul(xf.q, this.m_p));
  var d = Vec2.Sub(p, center);
  return Vec2.Dot(d, d) <= this.m_radius * this.m_radius;
}

// Collision Detection in Interactive 3D Environments by Gino van den Bergen
// From Section 3.1.2
// x = s + a * r
// norm(x) = radius
CircleShape.prototype.RayCast = function(output, input, xf, childIndex) {

  var position = Vec2.Add(xf.p, Vec2.Mul(xf.q, this.m_p));
  var s = Vec2.Sub(input.p1, position);
  var b = Vec2.Dot(s, s) - this.m_radius * this.m_radius;

  // Solve quadratic equation.
  var r = Vec2.Sub(input.p2, input.p1);
  var c = Vec2.Dot(s, r);
  var rr = Vec2.Dot(r, r);
  var sigma = c * c - rr * b;

  // Check for negative discriminant and short segment.
  if (sigma < 0.0 || rr < Math.EPSILON) {
    return false;
  }

  // Find the point of intersection of the line with the circle.
  var a = -(c + Math.sqrt(sigma));

  // Is the intersection point on the segment?
  if (0.0 <= a && a <= input.maxFraction * rr) {
    a /= rr;
    output.fraction = a;
    output.normal = Vec2.Add(s, Vec2.Mul(a, r));
    output.normal.Normalize();
    return true;
  }

  return false;
}

CircleShape.prototype.ComputeAABB = function(aabb, xf, childIndex) {
  var p = Vec2.Add(xf.p, Rot.Mul(xf.q, this.m_p));
  aabb.lowerBound.Set(p.x - this.m_radius, p.y - this.m_radius);
  aabb.upperBound.Set(p.x + this.m_radius, p.y + this.m_radius);
}

CircleShape.prototype.ComputeMass = function(massData, density) {
  massData.mass = density * Math.PI * this.m_radius * this.m_radius;
  massData.center = this.m_p;
  // inertia about the local origin
  massData.I = massData.mass
      * (0.5 * this.m_radius * this.m_radius + Vec2.Dot(this.m_p, this.m_p));
}

CircleShape.prototype.ComputeDistanceProxy = function(proxy) {
  proxy.m_vertices.push(this.m_p);
  proxy.m_count = 1;
  proxy.m_radius = this.m_radius;
};