java - 静止后 JMonkey 物理对象被卡住在适当的位置

Question

这是 JME3 教程中 HelloPhysics 的一个非常简单的扩展。当您点击一 block 砖 block 时，该砖 block 就会从游戏和物理空间中移除。如果你移走砖 block 的速度足够快，在墙沉降之前，它就会像你想象的那样崩塌，但如果你在移走砖 block 之前稍等一下，就什么也不会发生。

我认为物体停止移动后物理功能会关闭，以防止过度抖动，并且我想再次手动启动它。

package jme3test.helloworld;

import com.jme3.app.SimpleApplication;
import com.jme3.asset.TextureKey;
import com.jme3.bullet.BulletAppState;
import com.jme3.bullet.control.RigidBodyControl;
import com.jme3.collision.CollisionResult;
import com.jme3.collision.CollisionResults;
import com.jme3.font.BitmapText;
import com.jme3.input.KeyInput;
import com.jme3.input.MouseInput;
import com.jme3.input.controls.ActionListener;
import com.jme3.input.controls.KeyTrigger;
import com.jme3.input.controls.MouseButtonTrigger;
import com.jme3.material.Material;
import com.jme3.math.Ray;
import com.jme3.math.Vector2f;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.Node;
import com.jme3.scene.shape.Box;
import com.jme3.scene.shape.Sphere;
import com.jme3.scene.shape.Sphere.TextureMode;
import com.jme3.texture.Texture;
import com.jme3.texture.Texture.WrapMode;


/**
 * Example 12 - how to give objects physical properties so they bounce and fall.
 * @author base code by double1984, updated by zathras
 */
class HelloPhysics extends SimpleApplication {

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

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

  /** Prepare Materials */
  Material wall_mat;
  Material stone_mat;
  Material floor_mat;

  /** Prepare geometries and physical nodes for bricks and cannon balls. */
  Node removables;
  private RigidBodyControl    brick_phy;
  private static final Box    box;
  private RigidBodyControl    ball_phy;
  private static final Sphere sphere;
  private RigidBodyControl    floor_phy;
  private static final Box    floor;

  /** dimensions used for bricks and wall */
  private static final float brickLength = 0.48f;
  private static final float brickWidth  = 0.24f;
  private static final float brickHeight = 0.12f;

  static {
    /** Initialize the cannon ball geometry */
    sphere = new Sphere(32, 32, 0.4f, true, false);
    sphere.setTextureMode(TextureMode.Projected);
    /** Initialize the brick geometry */
    box = new Box(Vector3f.ZERO, brickLength, brickHeight, brickWidth);
    box.scaleTextureCoordinates(new Vector2f(1f, .5f));
    /** Initialize the floor geometry */
    floor = new Box(Vector3f.ZERO, 10f, 0.1f, 5f);
    floor.scaleTextureCoordinates(new Vector2f(3, 6));
  }

  @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);
    /** Add InputManager action: Left click triggers shooting. */
    inputManager.addMapping("shoot", 
            new MouseButtonTrigger(MouseInput.BUTTON_LEFT));
    inputManager.addListener(actionListener, "shoot");
    removables = new Node("Removables");
    rootNode.attachChild(removables);
    /** Initialize the scene, materials, and physics space */
    initMaterials();
    initWall();
    initFloor();
    initKeys();
    initCrossHairs();
  }
    /** Declaring the "Shoot" action and mapping to its triggers. */
  private void initKeys() {
    inputManager.addMapping("Shoot",
      new KeyTrigger(KeyInput.KEY_SPACE), // trigger 1: spacebar
      new MouseButtonTrigger(MouseInput.BUTTON_LEFT)); // trigger 2: left-button click
    inputManager.addListener(actionListener, "Shoot");
  }
  /** Initialize the materials used in this scene. */
  public void initMaterials() {
    wall_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    TextureKey key = new TextureKey("Textures/Terrain/BrickWall/BrickWall.jpg");
    key.setGenerateMips(true);
    Texture tex = assetManager.loadTexture(key);
    wall_mat.setTexture("ColorMap", tex);

    stone_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    TextureKey key2 = new TextureKey("Textures/Terrain/Rock/Rock.PNG");
    key2.setGenerateMips(true);
    Texture tex2 = assetManager.loadTexture(key2);
    stone_mat.setTexture("ColorMap", tex2);

    floor_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    TextureKey key3 = new TextureKey("Textures/Terrain/Pond/Pond.jpg");
    key3.setGenerateMips(true);
    Texture tex3 = assetManager.loadTexture(key3);
    tex3.setWrap(WrapMode.Repeat);
    floor_mat.setTexture("ColorMap", tex3);
  }

  /** 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() {
    float startpt = brickLength / 4;
    float height = 0;
    for (int j = 0; j < 15; j++) {
      for (int i = 0; i < 6; i++) {
        Vector3f vt =
         new Vector3f(i * brickLength * 2 + startpt, brickHeight + height, 0);
        makeBrick(vt);
      }
      startpt = -startpt;
      height += 2 * brickHeight;
    }
  }
  /** This method creates one individual physical brick. */
  public void makeBrick(Vector3f loc) {
    /** Create a brick geometry and attach to scene graph. */
    Geometry brick_geo = new Geometry("brick", box);
    brick_geo.setMaterial(wall_mat);
    /** Position the brick geometry  */
    brick_geo.setLocalTranslation(loc);
    /** Make brick physical with a mass > 0.0f. */
    brick_phy = new RigidBodyControl(2f);

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

  }

  /** This method creates one individual physical cannon ball.
   * By defaul, the ball is accelerated and flies
   * from the camera position in the camera direction.*/
   public void makeCannonBall() {
    /** Create a cannon ball geometry and attach to scene graph. */
    Geometry ball_geo = new Geometry("cannon ball", sphere);
    ball_geo.setMaterial(stone_mat);
    rootNode.attachChild(ball_geo);
    /** Position the cannon ball  */
    ball_geo.setLocalTranslation(cam.getLocation());
    /** Make the ball physcial with a mass > 0.0f */
    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(cam.getDirection().mult(25));
  }
    private ActionListener actionListener = new ActionListener() {

    public void onAction(String name, boolean keyPressed, float tpf) {
      if (name.equals("Shoot") && !keyPressed) {
        // 1. Reset results list.
        CollisionResults results = new CollisionResults();
        // 2. Aim the ray from cam loc to cam direction.
        Ray ray = new Ray(cam.getLocation(), cam.getDirection());
        // 3. Collect intersections between Ray and Shootables in results list.
        removables.collideWith(ray, results);
        // 4. Print the results
        System.out.println("----- Collisions? " + results.size() + "-----");
        for (int i = 0; i < results.size(); i++) {
          // For each hit, we know distance, impact point, name of geometry.
          float dist = results.getCollision(i).getDistance();
          Vector3f pt = results.getCollision(i).getContactPoint();
          String hit = results.getCollision(i).getGeometry().getName();
          System.out.println("* Collision #" + i);
          System.out.println("  You shot " + hit + " at " + pt + ", " + dist + " wu away.");
        }
        // 5. Use the results (we mark the hit object)
        if (results.size() > 0) {
          // The closest collision point is what was truly hit:
          Geometry closest = results.getClosestCollision().getGeometry();
          // Let's interact - we mark the hit with a red dot.

          bulletAppState.getPhysicsSpace().remove(closest.getControl(0));
          removables.detachChild(closest);
          bulletAppState.getPhysicsSpace().clearForces();
          bulletAppState.getPhysicsSpace().applyGravity();
          System.out.println("removing a "+closest.getName());

        } 
      }
    }
  };
  /** A plus sign used as crosshairs to help the player with aiming.*/
  protected void initCrossHairs() {
    guiNode.detachAllChildren();
    guiFont = assetManager.loadFont("Interface/Fonts/Default.fnt");
    BitmapText ch = new BitmapText(guiFont, false);
    ch.setSize(guiFont.getCharSet().getRenderedSize() * 2);
    ch.setText("+");        // fake crosshairs :)
    ch.setLocalTranslation( // center
      settings.getWidth() / 2 - guiFont.getCharSet().getRenderedSize() / 3 * 2,
      settings.getHeight() / 2 + ch.getLineHeight() / 2, 0);
    guiNode.attachChild(ch);
  }
}

Answer 1

不移动 sleep 的对象

你最初的想法是正确的，当一个物体静止时，它就进入了 sleep 状态，这有很多原因；避免抖动是其中之一，但它也可以显着提高效率。

sleep 时，物体不会受到重力，因此如果您移除支撑它的物体，它不会注意到。

通常你不必担心这个；如果对象经历“物理引擎内部”的效果，例如涉及碰撞，它会自动唤醒。但是，如果您进行外部更改(例如删除对象)，则必须担心唤醒对象。

唤醒可能受外部变化影响的对象

您可以通过调用.activate()来唤醒正在 hibernate 的对象。关于rigidBodyControl ，记住 sleep 是按每个对象进行的，因此您可能需要唤醒超过 1 个对象。

目前该程序并未跟踪所有 RigidBodyControl所以我添加了 HashSet<RigidBodyControl>()为了容纳它们，当将一 block 砖 block 添加到场景中时，它是 rigidBodyControl应该添加到这个哈希集中，当它从场景中删除时，它应该从哈希集中删除。

为了获得有效的解决方案，您应该只唤醒可能受到删除影响的对象，但在这种情况下，它可能是所有内容，我只是通过运行所有 HashSet<RigidBodyControl>() 来唤醒所有内容。并调用activate()在他们身上。

演示这些更改的完整程序如下所示

public class HelloPhysics extends SimpleApplication {
    
    public static void main(String args[]) {
        HelloPhysics app = new HelloPhysics();
        app.start();
    }
    
    /** Prepare the Physics Application State (jBullet) */
    private BulletAppState bulletAppState;
    
    /** Prepare Materials */
    Material wall_mat;
    Material stone_mat;
    Material floor_mat;
    
    /** Prepare geometries and physical nodes for bricks and cannon balls. */
    Node removables;
    
    private static final Box    box;
    private RigidBodyControl    ball_phy;
    private static final Sphere sphere;
    private RigidBodyControl    floor_phy;
    private static final Box    floor;
    
    private static Collection<RigidBodyControl> objectsThatNeedWaking=new HashSet<RigidBodyControl>();
    
    /** dimensions used for bricks and wall */
    private static final float brickLength = 0.48f;
    private static final float brickWidth  = 0.24f;
    private static final float brickHeight = 0.12f;
    
    static {
        /** Initialize the cannon ball geometry */
        sphere = new Sphere(32, 32, 0.4f, true, false);
        sphere.setTextureMode(TextureMode.Projected);
        /** Initialize the brick geometry */
        box = new Box(Vector3f.ZERO, brickLength, brickHeight, brickWidth);
        box.scaleTextureCoordinates(new Vector2f(1f, .5f));
        /** Initialize the floor geometry */
        floor = new Box(Vector3f.ZERO, 10f, 0.1f, 5f);
        floor.scaleTextureCoordinates(new Vector2f(3, 6));
    }
    
    @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);
        /** Add InputManager action: Left click triggers shooting. */
        inputManager.addMapping("shoot",
                new MouseButtonTrigger(MouseInput.BUTTON_LEFT));
        inputManager.addListener(actionListener, "shoot");
        removables = new Node("Removables");
        rootNode.attachChild(removables);
        /** Initialize the scene, materials, and physics space */
        initMaterials();
        initWall();
        initFloor();
        initKeys();
        initCrossHairs();
    }
    /** Declaring the "Shoot" action and mapping to its triggers. */
    private void initKeys() {
        inputManager.addMapping("Shoot",
                new KeyTrigger(KeyInput.KEY_SPACE), // trigger 1: spacebar
                new MouseButtonTrigger(MouseInput.BUTTON_LEFT)); // trigger 2: left-button click
        inputManager.addListener(actionListener, "Shoot");
    }
    /** Initialize the materials used in this scene. */
    public void initMaterials() {
        wall_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        TextureKey key = new TextureKey("Textures/Terrain/BrickWall/BrickWall.jpg");
        key.setGenerateMips(true);
        Texture tex = assetManager.loadTexture(key);
        wall_mat.setTexture("ColorMap", tex);
        
        stone_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        TextureKey key2 = new TextureKey("Textures/Terrain/Rock/Rock.PNG");
        key2.setGenerateMips(true);
        Texture tex2 = assetManager.loadTexture(key2);
        stone_mat.setTexture("ColorMap", tex2);
        
        floor_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        TextureKey key3 = new TextureKey("Textures/Terrain/Pond/Pond.jpg");
        key3.setGenerateMips(true);
        Texture tex3 = assetManager.loadTexture(key3);
        tex3.setWrap(WrapMode.Repeat);
        floor_mat.setTexture("ColorMap", tex3);
    }
    
    /** 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() {
        float startpt = brickLength / 4;
        float height = 0;
        for (int j = 0; j < 15; j++) {
            for (int i = 0; i < 6; i++) {
                Vector3f vt =
                        new Vector3f(i * brickLength * 2 + startpt, brickHeight + height, 0);
                makeBrick(vt);
            }
            startpt = -startpt;
            height += 2 * brickHeight;
        }
    }
    /** This method creates one individual physical brick. */
    public void makeBrick(Vector3f loc) {
        /** Create a brick geometry and attach to scene graph. */
        Geometry brick_geo = new Geometry("brick", box);
        brick_geo.setMaterial(wall_mat);
        /** Position the brick geometry  */
        brick_geo.setLocalTranslation(loc);
        /** Make brick physical with a mass > 0.0f. */
        RigidBodyControl brick_phy = new RigidBodyControl(2f);
        
        objectsThatNeedWaking.add(brick_phy);
        
        
        /** Add physical brick to physics space. */
        brick_geo.addControl(brick_phy);
        
        
        bulletAppState.getPhysicsSpace().add(brick_phy);
        removables.attachChild(brick_geo);
        
    }
    
    /** This method creates one individual physical cannon ball.
     * By defaul, the ball is accelerated and flies
     * from the camera position in the camera direction.*/
    public void makeCannonBall() {
        /** Create a cannon ball geometry and attach to scene graph. */
        Geometry ball_geo = new Geometry("cannon ball", sphere);
        ball_geo.setMaterial(stone_mat);
        rootNode.attachChild(ball_geo);
        /** Position the cannon ball  */
        ball_geo.setLocalTranslation(cam.getLocation());
        /** Make the ball physcial with a mass > 0.0f */
        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(cam.getDirection().mult(25));
    }
    private ActionListener actionListener = new ActionListener() {
        
        public void onAction(String name, boolean keyPressed, float tpf) {
            if (name.equals("Shoot") && !keyPressed) {
                // 1. Reset results list.
                CollisionResults results = new CollisionResults();
                // 2. Aim the ray from cam loc to cam direction.
                Ray ray = new Ray(cam.getLocation(), cam.getDirection());
                // 3. Collect intersections between Ray and Shootables in results list.
                removables.collideWith(ray, results);
                // 4. Print the results
                System.out.println("----- Collisions? " + results.size() + "-----");
                for (int i = 0; i < results.size(); i++) {
                    // For each hit, we know distance, impact point, name of geometry.
                    float dist = results.getCollision(i).getDistance();
                    Vector3f pt = results.getCollision(i).getContactPoint();
                    String hit = results.getCollision(i).getGeometry().getName();
                    System.out.println("* Collision #" + i);
                    System.out.println("  You shot " + hit + " at " + pt + ", " + dist + " wu away.");
                }
                // 5. Use the results (we mark the hit object)
                if (results.size() > 0) {
                    // The closest collision point is what was truly hit:
                    Geometry closest = results.getClosestCollision().getGeometry();
                    // Let's interact - we mark the hit with a red dot.
                    
                    bulletAppState.getPhysicsSpace().remove(closest.getControl(0));
                    objectsThatNeedWaking.remove(closest.getControl(0));
                    removables.detachChild(closest);
                    bulletAppState.getPhysicsSpace().clearForces();
                    bulletAppState.getPhysicsSpace().applyGravity();
                    System.out.println("removing a "+closest.getName());
                    
                    for(RigidBodyControl wakeMeUp: objectsThatNeedWaking){
                        wakeMeUp.activate();
                    }
                    
                }
            }
        }
    };
    /** A plus sign used as crosshairs to help the player with aiming.*/
    protected void initCrossHairs() {
        guiNode.detachAllChildren();
        guiFont = assetManager.loadFont("Interface/Fonts/Default.fnt");
        BitmapText ch = new BitmapText(guiFont, false);
        ch.setSize(guiFont.getCharSet().getRenderedSize() * 2);
        ch.setText("+");        // fake crosshairs :)
        ch.setLocalTranslation( // center
                settings.getWidth() / 2 - guiFont.getCharSet().getRenderedSize() / 3 * 2,
                settings.getHeight() / 2 + ch.getLineHeight() / 2, 0);
        guiNode.attachChild(ch);
    }
}