Package net.phys2d.raw.collide

Source Code of net.phys2d.raw.collide.LineCircleCollider

/*
* Phys2D - a 2D physics engine based on the work of Erin Catto.
*
* This source is provided under the terms of the BSD License.
*
* Copyright (c) 2006, Phys2D
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
*  * Redistributions of source code must retain the above
*    copyright notice, this list of conditions and the
*    following disclaimer.
*  * Redistributions in binary form must reproduce the above
*    copyright notice, this list of conditions and the following
*    disclaimer in the documentation and/or other materials provided
*    with the distribution.
*  * Neither the name of the Phys2D/New Dawn Software nor the names of
*    its contributors may be used to endorse or promote products
*    derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
* OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
* OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
* TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
* OF SUCH DAMAGE.
*/
package net.phys2d.raw.collide;

import net.phys2d.math.ROVector2f;
import net.phys2d.math.Vector2f;
import net.phys2d.raw.Body;
import net.phys2d.raw.Contact;
import net.phys2d.raw.shapes.Circle;
import net.phys2d.raw.shapes.Line;

/**
* Collision routines betwene a circle and a line. The create method is
* provided in case this collider becomes stateful at some point.
*
* @author Kevin Glass
*/
public strictfp class LineCircleCollider implements Collider {

  /**
   * @see net.phys2d.raw.collide.Collider#collide(net.phys2d.raw.Contact[], net.phys2d.raw.Body, net.phys2d.raw.Body)
   */
  public int collide(Contact[] contacts, Body bodyA, Body bodyB) {
    Line line = (Line) bodyA.getShape();
    Circle circle = (Circle) bodyB.getShape();
   
    Vector2f[] vertsA = line.getVertices(bodyA.getPosition(), bodyA.getRotation());
   
    // compute intersection of the line A and a line parallel to
    // the line A's normal passing through the origin of B
    Vector2f startA = vertsA[0];
    Vector2f endA = vertsA[1];
    ROVector2f startB = bodyB.getPosition();
    Vector2f endB = new Vector2f(endA);
    endB.sub(startA);
    endB.set(endB.y, -endB.x);
//    endB.add(startB);// TODO: inline endB into equations below, this last operation will be useless..
   
    //TODO: reuse mathutil.intersect
//    float d = (endB.y - startB.getY()) * (endA.x - startA.x);
//    d -= (endB.x - startB.getX()) * (endA.y - startA.y);
//   
//    float uA = (endB.x - startB.getX()) * (startA.y - startB.getY());
//    uA -= (endB.y - startB.getY()) * (startA.x - startB.getX());
//    uA /= d;
    float d = endB.y * (endA.x - startA.x);
    d -= endB.x * (endA.y - startA.y);
   
    float uA = endB.x * (startA.y - startB.getY());
    uA -= endB.y * (startA.x - startB.getX());
    uA /= d;
   
    Vector2f position = null;
   
    if ( uA < 0 ) { // the intersection is somewhere before startA
      position = startA;
    } else if ( uA > 1 ) { // the intersection is somewhere after endA
      position = endA;
    } else {
      position = new Vector2f(
          startA.x + uA * (endA.x - startA.x),
          startA.y + uA * (endA.y - startA.y));
    }
   
    Vector2f normal = endB; // reuse of vector object
    normal.set(startB);
    normal.sub(position);
    float distSquared = normal.lengthSquared();
    float radiusSquared = circle.getRadius() * circle.getRadius();
   
    if ( distSquared < radiusSquared ) {
      contacts[0].setPosition(position);
      contacts[0].setFeature(new FeaturePair());
     
      normal.normalise();
      contacts[0].setNormal(normal);
     
      float separation = (float) Math.sqrt(distSquared) - circle.getRadius();
      contacts[0].setSeparation(separation);
     
      return 1;
    }
   
    return 0;
  }

}
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