planck-js/lib/shape/EdgeShape.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 = EdgeShape;

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');

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

EdgeShape.TYPE = 'edge';

/**
 * A line segment (edge) shape. These can be connected in chains or loops to
 * other edge shapes. The connectivity information is used to ensure correct
 * contact normals.
 */
function EdgeShape(v1, v2) {
  if (!(this instanceof EdgeShape)) {
    return new EdgeShape(v1, v2);
  }

  EdgeShape._super.call(this);

  this.m_type = EdgeShape.TYPE;
  this.m_radius = Settings.polygonRadius;

  // These are the edge vertices
  this.m_vertex1 = Vec2(v1);
  this.m_vertex2 = Vec2(v2);

  // Optional adjacent vertices. These are used for smooth collision.
  // Used by chain shape.
  this.m_vertex0 = Vec2();
  this.m_vertex3 = Vec2();
  this.m_hasVertex0 = false;
  this.m_hasVertex3 = false;
}

/**
 * Set this as an isolated edge.
 */
EdgeShape.prototype.Set = function(v1, v2) {
  this.m_vertex1.Set(v1);
  this.m_vertex2.Set(v2);
  this.m_hasVertex0 = false;
  this.m_hasVertex3 = false;
  return this;
}

EdgeShape.prototype.Clone = function() {
  var clone = new EdgeShape();
  clone.m_type = this.m_type;
  clone.m_radius = this.m_radius;
  clone.m_vertex1.Set(this.m_vertex1);
  clone.m_vertex2.Set(this.m_vertex2);
  clone.m_vertex0.Set(this.m_vertex0);
  clone.m_vertex3.Set(this.m_vertex3);
  clone.m_hasVertex0 = this.m_hasVertex0;
  clone.m_hasVertex3 = this.m_hasVertex3;
  return clone;
}

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

EdgeShape.prototype.TestPoint = function(xf, p) {
  return false;
}

// p = p1 + t * d
// v = v1 + s * e
// p1 + t * d = v1 + s * e
// s * e - t * d = p1 - v1
EdgeShape.prototype.RayCast = function(output, input, xf, childIndex) {
  // NOT_USED(childIndex);

  // Put the ray into the edge's frame of reference.
  var p1 = Vec2.MulT(xf.q, Vec2.Sub(input.p1, xf.p));
  var p2 = Vec2.MulT(xf.q, Vec2.Sub(input.p2, xf.p));
  var d = Vec2.Sub(p2, p1);

  var v1 = this.m_vertex1;
  var v2 = this.m_vertex2;
  var e = Vec2.Sub(v2, v1);
  var normal = Vec2(e.y, -e.x);
  normal.Normalize();

  // q = p1 + t * d
  // dot(normal, q - v1) = 0
  // dot(normal, p1 - v1) + t * dot(normal, d) = 0
  var numerator = Vec2.Dot(normal, Vec2.Sub(v1, p1));
  var denominator = Vec2.Dot(normal, d);

  if (denominator == 0.0) {
    return false;
  }

  var t = numerator / denominator;
  if (t < 0.0 || input.maxFraction < t) {
    return false;
  }

  var q = Vec2.Add(p1, Vec2.Mul(t, d));

  // q = v1 + s * r
  // s = dot(q - v1, r) / dot(r, r)
  var r = Vec2.Sub(v2, v1);
  var rr = Vec2.Dot(r, r);
  if (rr == 0.0) {
    return false;
  }

  var s = Vec2.Dot(Vec2.Sub(q - v1), r) / rr;
  if (s < 0.0 || 1.0 < s) {
    return false;
  }

  output.fraction = t;
  if (numerator > 0.0) {
    output.normal = -Vec2.Mul(xf.q, normal);
  } else {
    output.normal = Vec2.Mul(xf.q, normal);
  }
  return true;
}

EdgeShape.prototype.ComputeAABB = function(aabb, xf, childIndex) {
  var v1 = Transform.Mul(xf, this.m_vertex1);
  var v2 = Transform.Mul(xf, this.m_vertex2);

  aabb.CombinePoints(v1, v2);
  aabb.Extend(this.m_radius)
}

EdgeShape.prototype.ComputeMass = function(massData, density) {
  massData.mass = 0.0;
  massData.center.WSet(0.5, this.m_vertex1, 0.5, this.m_vertex2);
  massData.I = 0.0;
}

EdgeShape.prototype.ComputeDistanceProxy = function(proxy) {
  proxy.m_vertices.push(this.m_vertex1);
  proxy.m_vertices.push(this.m_vertex2);
  proxy.m_count = 2;
  proxy.m_radius = this.m_radius;
};