JMonkeyEngine-几何相交NullPointerException

Question

我是3d引擎的新手，当我试图碰撞一个几何和一个NullPointerException物体时，我得到了这个3D引擎。

以下是我如何声明我的目标(对不起，目前相当混乱)

    public void simpleInitApp() {



    Quad q= new Quad(100, 100);
    Dome mesh = new Dome(Vector3f.ZERO, 2, 32, 1f,false);

     geom = new Geometry("Cylinder", mesh); //declared elsewhere

     g3 = new Geometry("lel", q);
    Material mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Blue);
    Material mat2 = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    mat2.setColor("Color", ColorRGBA.Red);
    geom.setMaterial(mat);

    g3.setMaterial(mat2);

    rootNode.attachChild(geom);
    rootNode.attachChild(g3);

这是我的更新循环

public void simpleUpdate(float tpf) {

    // System.out.println("hi");
    BoundingVolume b = g3.getWorldBound(); //should give boundingvolume of the quad

    System.out.println(b.getVolume()); //just to test if this works
    CollisionResults r2 = new CollisionResults(); //declare and initialize the collisionresults
    geom.collideWith(b, r2); //collide
    System.out.println(r2.size()); //this returns a value, usually between 0-2


    for(CollisionResult x:r2){


       System.out.println("x = "+ x.getContactPoint().getX()); 
  /*and oddly enough, i get a NullPointerException here even though the collision appeared successful - this never prints anything either so it's not going out of bounds or anything*/


    }


}

当我试图从一个NullPointerException和一个几何的交集中打印出每个CollisionResult的坐标时，得到一个BoundingVolume。

JMonkey论坛和JMonkey文档似乎都没有任何帮助。你们谁能帮上忙？提前谢谢。

Answer 1

你的模型不附属于JBullet物理。试着像这样：

BulletAppState buleltAppState;

public void simpleInitApp() {

    Quad q= new Quad(100, 100);
    Dome mesh = new Dome(Vector3f.ZERO, 2, 32, 1f,false);

    geom = new Geometry("Cylinder", mesh); //declared elsewhere

    g3 = new Geometry("lel", q);
    Material mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Blue);
    Material mat2 = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    mat2.setColor("Color", ColorRGBA.Red);
    geom.setMaterial(mat);

    g3.setMaterial(mat2);

    bulletAppState = new BulletAppState();
    stateManager.attach(bulletAppState);
    bulletAppState.getPhysicsSpace().attachChild(geom);
    bulletAppState.getPhysicsSpace().attachChild(g3);

    rootNode.attachChild(geom);
    rootNode.attachChild(g3);
}

在那之后，你可以检查碰撞！

Answer 2

我做了一些研究，我相信问题是，在二维/三维物体之间没有单一的碰撞点，而是有一个2D/3D碰撞区域。因此，如果没有单点可用，则返回null。这是由开发人员的评论备份的。我相信JMonkey碰撞检测实际上并不计算相交区域，因为它在数学上非常复杂(虽然它确实给出了碰撞中涉及的三角形)

如果你的两种形状都是凸的，你可能会对计算三维多边形交叉口的文章感兴趣：求两个三维多边形的相交。