java - jmonkeyengine 移动速度太快无法进行碰撞检测

Question

我正在使用 JMonkeyEngine 制作一个 Java 游戏，我已经按照他们网站上的教程向墙上射球(子弹)。我明白一切是如何运作的，但是当我增加子弹的速度时，它会直接穿过墙壁。

现在我知道发生这种情况的原因(因为子弹每帧移动速度太快，无法注册碰撞)。我也知道如何解决这个问题，我在他们的网站 ( JMonkeyEngine ) 上找到了以下方法。

setCcdMotionThreshold(0f)

但是谁能告诉我这是如何实现的，或者我在哪里可以找到使用它的人的样本？

Answer 1

简介
连续碰撞检测 (ccd) 处理子弹与纸的问题。快速移动的物体在一个时间步是薄物体的一侧，而在下一个时间步是另一侧，导致物理引擎认为根本没有发生碰撞。另一方面，连续碰撞检测根本不使用时间步长。它在整个时间步长期间创建一个扫描体积，并查看该扫描体积是否与任何东西发生碰撞。这既昂贵又不准确(因为为此使用了简单的圆形碰撞形状而不是完整的碰撞形状)。

用法
Continuous collision detection 是在每个对象基础上设置的，你可以同时在同一场景中有使用 ccd 的对象和不使用 ccd 的对象，ccd 是在物理对象上设置的，如下所示

RigidBodyControl physicsObject = new RigidBodyControl(mass);
physicsObject.setCcdMotionThreshold(expectedWidthOfThinObject);
physicsObject.setCcdSweptSphereRadius(radiusOfSphereThatWillFullyContainObject);

• 您想将 expectedWidthOfThinObject 设置得尽可能高和;请记住 ccd 昂贵且不准确。将其设置为零将关闭 ccd
• 您想在完全包含对象的同时将 radiusOfSphereThatWillFullyContainObject 设置得尽可能小

完整示例
以下源代码将显示使用连续碰撞检测 和使用标准碰撞检测之间的区别。它发射两组球，一组快，一组慢，并以 5 秒的间隔打开和关闭 ccd。慢球总是与纸碰撞，快球只有在 ccd 打开时才会碰撞。

import com.jme3.app.SimpleApplication;
import com.jme3.bullet.BulletAppState;
import com.jme3.bullet.control.RigidBodyControl;
import com.jme3.font.BitmapText;
import com.jme3.material.Material;
import com.jme3.math.ColorRGBA;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.shape.Box;
import com.jme3.scene.shape.Sphere;

public class BulletTest extends SimpleApplication {

  public static void main(String args[]) {
    BulletTest app = new BulletTest();
    app.start();
  }

  /** Prepare the Physics Application State (jBullet) */
  private BulletAppState bulletAppState;

  /** Prepare Materials */
  Material wall_mat;
  Material slow_mat;
  Material fast_mat;
  Material floor_mat;


  private RigidBodyControl    brick_phy;
  private static final Box    box;
  private static final Sphere sphere;
  private RigidBodyControl    floor_phy;
  private static final Box    floor;

  /** dimensions used for wall */
  private static final float brickLength = 2f;
  private static final float brickWidth  = 0.015f;
  private static final float brickHeight = 1f;

  static {
    /** Initialize the cannon ball geometry */
    sphere = new Sphere(32, 32, 0.1f, true, false);
    /** Initialize the brick geometry */
    box = new Box(brickWidth, brickHeight, brickLength);
    /** Initialize the floor geometry */
    floor = new Box(10f, 0.1f, 5f);

  }

  @Override
  public void simpleInitApp() {
    /** Set up Physics Game */
    bulletAppState = new BulletAppState();
    stateManager.attach(bulletAppState);
    //bulletAppState.getPhysicsSpace().enableDebug(assetManager);

    /** Configure cam to look at scene */
    cam.setLocation(new Vector3f(0, 4f, 6f));
    cam.lookAt(new Vector3f(2, 2, 0), Vector3f.UNIT_Y);

    /** Initialize the scene, materials, and physics space */
    initMaterials();
    initWall();
    initFloor();
    setUpHUDText();
  }

  public static final float FIREPERIOD=0.5f;
  double fireTimer=0;

  public static final float SWEEPPERIOD=5f;
  double sweepTimer=0;
  boolean continuouslySweeping=true;


    @Override
    public void simpleUpdate(float tpf) {
        fireTimer+=tpf;
        sweepTimer+=tpf;

        if (sweepTimer>SWEEPPERIOD){
            sweepTimer=0;
            continuouslySweeping=!continuouslySweeping;
        }

        hudText.setText("ContinouslySweeping=" + continuouslySweeping + "(" + (int)(SWEEPPERIOD-sweepTimer) + ")" );

        if (fireTimer>FIREPERIOD){
            fireTimer=0;
            makeCannonBall(new Vector3f(-4,3,0),new Vector3f(6,4,0),slow_mat,continuouslySweeping); //slow arcing ball
            makeCannonBall(new Vector3f(-4,3,-0.5f),new Vector3f(10,1,0),fast_mat,continuouslySweeping); //fast straight ball
        }
    }

    public BitmapText hudText;

    private void setUpHUDText(){
        hudText = new BitmapText(guiFont, false);          
        hudText.setSize(guiFont.getCharSet().getRenderedSize());      // font size
        hudText.setColor(ColorRGBA.White);                             // font color
        hudText.setText("ContinouslySweeping=true");             // the text
        hudText.setLocalTranslation(300, hudText.getLineHeight(), 0); // position
        guiNode.attachChild(hudText);
    }

  /** Initialize the materials used in this scene. */
  public void initMaterials() {
    wall_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    wall_mat.setColor("Color", ColorRGBA.Blue);

    fast_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    fast_mat.setColor("Color", ColorRGBA.Red);

    slow_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    slow_mat.setColor("Color", ColorRGBA.Green);

    floor_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    floor_mat.setColor("Color", ColorRGBA.Gray);
  }

  /** Make a solid floor and add it to the scene. */
  public void initFloor() {
    Geometry floor_geo = new Geometry("Floor", floor);
    floor_geo.setMaterial(floor_mat);
    floor_geo.setLocalTranslation(0, -0.1f, 0);
    this.rootNode.attachChild(floor_geo);
    /* Make the floor physical with mass 0.0f! */
    floor_phy = new RigidBodyControl(0.0f);
    floor_geo.addControl(floor_phy);
    bulletAppState.getPhysicsSpace().add(floor_phy);
  }

  /** This loop builds a wall out of individual bricks. */
  public void initWall() {

        Vector3f location=new Vector3f(2,2,0);
        Geometry brick_geo = new Geometry("brick", box);
        brick_geo.setMaterial(wall_mat);
        rootNode.attachChild(brick_geo);
        /** Position the brick geometry  */
        brick_geo.setLocalTranslation(location);

        //paper thin objects will fall down, mass 0 clamps it in position
        brick_phy = new RigidBodyControl(0); 

        /** Add physical brick to physics space. */
        brick_geo.addControl(brick_phy);
        bulletAppState.getPhysicsSpace().add(brick_phy);
  }


  public void makeCannonBall(Vector3f startPoint, Vector3f initialVelocity, Material material, boolean continuouslySwept) {
        /** Create a cannon ball geometry and attach to scene graph. */
        Geometry ball_geo = new Geometry("cannon ball", sphere);
        ball_geo.setMaterial(material);
        rootNode.attachChild(ball_geo);
        /** Position the cannon ball  */
        ball_geo.setLocalTranslation(startPoint);
        /** Make the ball physcial with a mass > 0.0f */
        RigidBodyControl ball_phy = new RigidBodyControl(1f);
        /** Add physical ball to physics space. */
        ball_geo.addControl(ball_phy);
        bulletAppState.getPhysicsSpace().add(ball_phy);
        /** Accelerate the physcial ball to shoot it. */
        ball_phy.setLinearVelocity(initialVelocity);

        if (continuouslySwept){
            ball_phy.setCcdMotionThreshold(0.015f);
            ball_phy.setCcdSweptSphereRadius(0.01f);
        }

  }


}

连续检测到两组球的弹跳符合预期(球从左上角进入):

随着连续检测，一组快速的球(红色)穿过纸，就好像它不存在一样(偶尔也会有一个慢球(绿色)穿过纸):

注意:此代码大致基于 hello physics具有来自 advanced physics 的附加功能的代码