Examples of GJK

jinngine.collision.GJK
Implementation of the Gilbert-Johnsson-Keerthi algorithm, for computing the distance between convex objects and/or closest points. This implementation is based on the theory presented in [Bergen, 2003, Continuous Collision Detection in Interactive 3D environments, ISBN-13: 978-1558608016]. This describes an approach that is based on a recursive simplex reduction technique. This implementation us "unrolled", so that recursive calls are avoided.

Examples of jinngine.collision.GJK

  /*
   * Two spheres of radius 1 having a distance of 1.
   * Sphere 1 is at (0,3,0), Sphere 2 is at (0,0,0)
   */
  public void testSphereSphere1() {
    GJK gjk = new GJK();
    
    //set up geometries
    Sphere s1 = new Sphere(1);
    Body b1 = new Body("default", s1);
    b1.setPosition(new Vector3(0,3,0));
    Sphere s2 = new Sphere(1);
    Body b2 = new Body("default", s2);
    b2.setPosition(new Vector3(0,0,0));
    
    //closest point vectors
    Vector3 p1 = new Vector3();
    Vector3 p2 = new Vector3();
        
    gjk.run(s1,s2,p1,p2,Double.POSITIVE_INFINITY, epsilon, 31);
    
    double d = p1.sub(p2).norm();
    
    System.out.println( "d="+d);

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Examples of jinngine.collision.GJK

   * Sphere 1 is at (0,1+a,0), Sphere 2 is at (0,-1-a,0), 
   * where a is a small number. We expect the distance to 
   * be 2a, within the error tolerance
   */
  public void testSphereSphere2() {
    GJK gjk = new GJK();


    //small number
    double a = 1e-3;
        
    //set up geometries
    Sphere s1 = new Sphere(1);
    Body b1 = new Body("default", s1);
    b1.setPosition(new Vector3(0,1+a,0));
    Sphere s2 = new Sphere(1);
    Body b2 = new Body("default", s2);
    b2.setPosition(new Vector3(0,-1-a,0));
    
    //closest point vectors
    Vector3 p1 = new Vector3();
    Vector3 p2 = new Vector3();
        
    gjk.run(s1,s2,p1,p2,Double.POSITIVE_INFINITY, epsilon, 31);
    
    double d = p1.sub(p2).norm();
    System.out.println("d="+d);
    
    // distance should be 2a within precision

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Examples of jinngine.collision.GJK

  
  /**
   * Two spheres excactly overlapping each other
   */
  public void testOverlapSphere1() {
    GJK gjk = new GJK();
    
    //set up two spheres, occupying the exact same space
    Sphere s1 = new Sphere(1);
    Body b1 = new Body("default", s1);
    b1.setPosition(new Vector3(0,0,0));
    Sphere s2 = new Sphere(1);
    Body b2 = new Body("default", s2);
    b2.setPosition(new Vector3(0,0,0));
    
    //closest point vectors
    Vector3 p1 = new Vector3();
    Vector3 p2 = new Vector3();
        
    gjk.run(s1,s2,p1,p2,Double.POSITIVE_INFINITY, epsilon, 31);
    
    // we expect closest points to be the same
    assertTrue( p1.sub(p2).norm() < epsilon );
  }

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Examples of jinngine.collision.GJK

      Vector3 p1 = new Vector3();
      Vector3 p2 = new Vector3();


      // create a new gjk every time, to avoid the frame coherence 
      // heuristic inside GJK
      GJK gjk = new GJK();
      
      // when the distance between objects becomes close to zero, 
      // the gjk algorithm gegenerates and produces less acurate results.
      // therefore we use more iterations here
      gjk.run(s1,s2,p1,p2,Double.POSITIVE_INFINITY, epsilon, 2256);
      
      // we want the expected distance 
      assertTrue( Math.abs( p1.sub(p2).norm() - expected ) < epsilon );
    }
  }

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