身体移动时没有施加任何力? (Box2d) [英] Body moving without any force applied? (Box2d)

问题描述

所以我在方框2d中进行游戏.在一个部分中，我需要一个具有恒定弹跳高度的球.我将球的恢复力设置为1，并且不对其施加任何力(当然，重力除外).现在，这个球在每次弹跳时，每次弹跳都会更高一点，直到它离开屏幕的顶部边缘为止.此代码有什么问题?

So I am making a game in box 2d. In one part I need a ball which has a constant bounce height. I set the ball's restitution to 1 and am applying no force on it whatsoever (except gravity of course). Now this ball, on every bounce, bounces a bit higher everytime till it goes out of the top edge of the screen. What is wrong with this code?

    public class Ball implements ApplicationListener {
 World world ;  
 Box2DDebugRenderer debugRenderer;  
 OrthographicCamera camera;  
 static final float BOX_STEP=1/60f;  
 static final int BOX_VELOCITY_ITERATIONS=8;  
 static final int BOX_POSITION_ITERATIONS=3;  
 static final float WORLD_TO_BOX=0.01f;  
 static final float BOX_WORLD_TO=100f;  
 Rectangle ball;
 Body body;
 /* (non-Javadoc)
 * @see com.badlogic.gdx.ApplicationListener#create()
 */
@Override  
 public void create() {
     world = new World(new Vector2(0, -10), true);
      camera = new OrthographicCamera(); 

      camera.viewportHeight = 480;  
      camera.viewportWidth = 800;  
      camera.position.set(camera.viewportWidth * .5f, camera.viewportHeight * .5f, 0f);  
      camera.update();
      //Ground body  
      BodyDef groundBodyDef =new BodyDef();  
      groundBodyDef.position.set(new Vector2(0, 10 * WORLD_TO_BOX));  
      Body groundBody = world.createBody(groundBodyDef);  
      PolygonShape groundBox = new PolygonShape();
      float w = (camera.viewportWidth * 2) * WORLD_TO_BOX;
      float h = 10.0f * WORLD_TO_BOX;
      groundBox.setAsBox(w,h);  
      groundBody.createFixture(groundBox, 0.0f); 
      String a="gb";
      groundBody.setUserData(a);
      //Dynamic Body  
      BodyDef bodyDef = new BodyDef();  
      bodyDef.type = BodyType.DynamicBody;  
      float posX = (camera.viewportWidth / 8) * WORLD_TO_BOX;
      float posY = (camera.viewportHeight / 2) * WORLD_TO_BOX;
      bodyDef.position.set(posX, posY);
      body = world.createBody(bodyDef);  
   // create a Rectangle to logically represent the ball
      CircleShape dynamicCircle = new CircleShape();  
      dynamicCircle.setRadius(1f);  
      FixtureDef fixtureDef = new FixtureDef();  
      fixtureDef.shape = dynamicCircle;  
      fixtureDef.density = 1.0f;  
      fixtureDef.friction = 0.0f;  
      fixtureDef.restitution =1f;
      body.createFixture(fixtureDef);
      debugRenderer = new Box2DDebugRenderer();  
 }
 @Override  
 public void dispose() {  
 }  
 @Override  
 public void render() {            
      Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);  
      debugProjection.set(camera.combined);
      debugProjection.scl(BOX_WORLD_TO);
      debugRenderer.render(world, debugProjection);  
      world.step(BOX_STEP, BOX_VELOCITY_ITERATIONS, BOX_POSITION_ITERATIONS);
          }



 @Override  
 public void resize(int width, int height) {  
 }  
 @Override  
 public void pause() {  
 }  
 @Override  
 public void resume() {  
 }  
}

推荐答案

这可能是由于数值不稳定性.反复计算球的位置不可避免地会引入微小的数字误差(因为浮子只能容纳有限的数字).这些可能会不断增长，并在迭代之间累加起来，在反弹之间不断反弹.

This may be caused by numerical instability. Repeatedly calculating positions of your ball inevitably introduces tiny numerical errors (because a float can only hold a limited number of digits). These may grow and add up from iteration to iteration, bounce to bounce.

您可以尝试使用归还0.9999999之类的方法.但是很可能没有恢复原状的价值可以带来预期的结果.

You can try using restitution 0.9999999 or something. But chances are that there is no restitution value which gives desired results.

尝试积极补偿数值不稳定性，例如在您可以非迭代地计算值的情况下，通过控制球的位置和/或速度. (我不知道Box2D.也许当球撞到地面时，您可以重置其速度或其他东西.)

Try to actively compensate for the numerical instability e.g. by controlling the ball's position and/or velocity in situations in which you can calculate values non-iteratively. (I do not know Box2D. Maybe when the ball hits the ground you can reset its speed or something.)

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