Question

我正在使用JMonkeyEngine制作Java游戏，我已经按照他们网站上的教程在墙上射击球（子弹）。我知道一切是如何工作的，但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（因为子弹每帧移动得太快，无法进行碰撞注册）。我也知道如何解决这个问题，我在他们的网站上找到了以下方法（JMonkeyEngine）。

setCcdMotionThreshold(0f)

但有人能告诉我这是如何实施的，或者我可以在哪里找到使用此人的样本？

Answer 1

<强>简介
连续碰撞检测（ccd）处理子弹与纸张问题。快速移动的物体是一个时间步长的薄物体的一侧而下一个时间的另一个步骤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掠体积，并查找扫掠体积是否与任何物体发生碰撞。这既昂贵又不准确（因为使用简单的圆形碰撞形状而不是完整的碰撞形状）。

<强>用法
连续碰撞检测是基于每个对象设置的，你可以拥有使用ccd的对象和同时不在同一场景中的对象，ccd设置在物理对象上，如下所示

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

您希望将expectedWidthOfThinObject设置为高可以逃脱用;记得ccd昂贵且不准确。将其设置为零将关闭ccd
您希望在完全包含对象时将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，一组快速，一组慢，并以5秒的间隔打开和关闭ccd。缓慢的球总是与纸张碰撞，快速的球只有在打开ccd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);
        }

  }


}

连续检测两组球按预期弹跳（球从左上方进入）：
enter image description here

随着连续检测关闭，快速设置的球（红色）穿过纸张，好像它不在那里（并且偶尔也会慢一个（绿色））：
enter image description here

注意：此代码基于hello physics代码，并添加了advanced physics

的功能

jmonkeyengine运动速度太快，无法进行碰撞检测

1 个答案: