Android 2d物理引擎Box2d的使用示例

Box2d是一个很出名的2d物理引擎，大家可以google之。Box2d有C++，flash和Java等版本。android可以直接使用java版本的Jbox2d，但因为Jbox2d的图形渲染是使用processing库来实现的，所以，在android中使用Jbox2d的时候，图形渲染的工作就只能自己来写了。因为网上关于box2d的资料真的非常的少，特别是关于图形绘制方面，所以，虽然程序写得不是很好，还是贴上来了，先看截图：

 

 

 

 

程序很简单：蓝色的是地面，从上面掉下两个绿球和一个红色的方块，它们之间的碰撞都由box2d引擎自己来完成。

（这程序运行起来有点卡，我 也正在解决这个问题，有朋友知道答案的也请分享一下啦！）

代码如下：

package com.ray.test;

import org.jbox2d.collision.AABB;
import org.jbox2d.collision.CircleDef;
import org.jbox2d.collision.PolygonDef;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.Body;
import org.jbox2d.dynamics.BodyDef;
import org.jbox2d.dynamics.World;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;

public class MyBox2d extends Activity {
	
	private final static int RATE = 10;//屏幕到现实世界的比例 10px：1m;
	private AABB worldAABB;//创建 一个管理碰撞的世界
	private World world;
	private float timeStep = 1/60;//模拟的的频率
	private int iterations = 10;//迭代越大，模拟约精确，但性能越低
	private Body body,body2,body3;
	private MyView myView;
	private Handler mHandler;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams. FLAG_FULLSCREEN ,
        WindowManager.LayoutParams. FLAG_FULLSCREEN);
        
        worldAABB = new AABB();
         
       //上下界，以屏幕的左上方为 原点，如果创建的刚体到达屏幕的边缘的话，会停止模拟
        worldAABB.lowerBound.set(-100.0f,-100.0f)；
        worldAABB.upperBound.set(100.0f, 100.0f);//注意这里使用的是现实世界的单位
        
        Vec2 gravity = new Vec2(0.0f,10.0f);
        boolean doSleep = true;
        

        world = new World(worldAABB, gravity, doSleep);//创建世界
        
        createBox(160, 470, 160, 10, true);     
        createBox1(160, 150, 160, 10, false);
        
        createCircle(160, 100, 10);
        createCircle1(150, 60, 10);
        timeStep = 1.0f/60.0f;
        iterations = 10;
        
        myView = new MyView(this);
        setContentView(myView);
        mHandler = new Handler();
        mHandler.post(update);
    }
    
    private Runnable update = new Runnable() {
        public void run() {
            	world.step(timeStep, iterations);//开始模拟
            	Vec2 position = body.getPosition();
            	Vec2 position1 = body2.getPosition();
            	Vec2 position2 = body3.getPosition();
            	myView.x=position.x*RATE;
            	myView.y=position.y*RATE;
            	
            	myView.x1=position1.x*RATE; 
            	myView.y1=position1.y*RATE;
            	
            	myView.x2=position2.x*RATE;
            	myView.y2=position2.y*RATE;
                myView.update();
                mHandler.postDelayed(update, (long)timeStep*1000);
        }
    };
    
    public void createBox(float x,float y,float half_width,float half_height,
                     boolean isStatic){ 
    	PolygonDef shape = new PolygonDef();
    	if(isStatic){shape.density = 0;}
    	else{shape.density = 2.0f;}
    	shape.friction = 0.8f;
    	shape.restitution = 0.3f;
    	shape.setAsBox(half_width/RATE, half_height/RATE);
    	
    	BodyDef bodyDef = new BodyDef();
    	bodyDef.position.set(x/RATE, y/RATE);
    	Body body1= world.createBody(bodyDef);
    	body1.createShape(shape);
    	body1.setMassFromShapes();
    }
    
    public void createCircle(float x,float y,float radius){
    	CircleDef shape = new CircleDef();
    	shape.density = 7;
    	shape.friction = 0.2f;
    	shape.radius = radius/RATE;
    	
    	BodyDef bodyDef = new BodyDef();
    	bodyDef.position.set(x/RATE, y/RATE);
    	body2 = world.createBody(bodyDef);
    	body2.createShape(shape);
    	body2.setMassFromShapes();
    }
    
    public void createCircle1(float x,float y,float radius){
    	CircleDef shape = new CircleDef();
    	shape.density = 7;
    	shape.friction = 0.2f;
    	shape.radius = radius/RATE;
    	
    	BodyDef bodyDef = new BodyDef();
    	bodyDef.position.set(x/RATE, y/RATE);
    	body3 = world.createBody(bodyDef);
    	body3.createShape(shape);
    	body3.setMassFromShapes();
    }
    
    public void createBox1(float x,float y,float half_width,float half_height,
                   boolean isStatic){ 
    	PolygonDef shape = new PolygonDef();
    	if(isStatic){shape.density = 0;}
    	else{shape.density = 2.0f;}
    	shape.friction = 0.3f;
    	shape.setAsBox(half_width/RATE, half_height/RATE);
    	
    	BodyDef bodyDef = new BodyDef();
    	bodyDef.position.set(x/RATE, y/RATE);
    	body= world.createBody(bodyDef);
    	body.createShape(shape);
    	body.setMassFromShapes();
    }
    
    class MyView extends View{
    	Canvas canvas;
    	public float x=160,y=150;
    	public float x1=160,y1=100;
    	public float x2=150,y2=60;
		public MyView(Context context) {
			super(context);
		}

		public void drawBox(float x,float y){
			Paint mPaint = new Paint();
			mPaint.setAntiAlias(true);
			mPaint.setColor(Color.RED);
			canvas.drawRect(x-160, y-10, x+160, y+10, mPaint);
		}
		
		public void drawGround(){
			Paint mPaint = new Paint();
			mPaint.setAntiAlias(true);
			mPaint.setColor(Color.BLUE);
			canvas.drawRect(0, 460, 320, 480, mPaint);
		}
		
		public void drawCircle(float x1,float y1){
			Paint mPaint = new Paint();
			mPaint.setAntiAlias(true);
			mPaint.setColor(Color.GREEN);
			canvas.drawCircle(x1, y1, 10, mPaint);
		}
		
		public void update(){
			postInvalidate();
		}
		
		protected void onDraw(Canvas canvas) {
			super.onDraw(canvas);
			this.canvas = canvas;
			drawGround();
			drawBox(x, y);
			drawCircle(x1, y1);
			drawCircle(x2, y2);
		}
		
    	
    }
}

 程序运行的时候需要加载Jbox2d的库，可到以下地址下载（使用的是不带渲染部分的库jbox2d-2.0.1-library-only.jar）：

http://sourceforge.net/projects/jbox2d/

这里有人移植box2d
http://code.google.com/p/androidbox2d/
不过看他的截图帧率仍然不能满足游戏或应用要求啊，
以前我看过一个OECAKE在iphone上的演示视频，流体，刚体，气体都表现得很完美，一点都不卡，不知道怎么优化的

view挺慢的吧，应该用SurfaceView

恩，我也用过SurfaceView，感觉差不多。另外还用了一下NDK版本的Box2d，那个性能比较好！

多谢楼主分享!  Java版的box2d确实比C/C++版的要慢, mobile gaming这一点, java确实不合适(至上目前是这样).  iPhone上是用的C/C++版, 很流畅!

我觉得JAVA版本box2d运行速度不行的原因在于它的垃圾回收机制，物理引擎里面使用的大量的而有生命周期很短的数据结构得不到及时回收。

iphone 的BOX2D 上有很多例子
查阅 cocos2d-iphone

嗯, JVM这个问题, 短期内在手机和嵌入式硬件上还不会得到完美解决...

Box2D的Android NDK移植版本
http://hi.baidu.com/gamefish/blog/item/1cb236fa3e1f31809f5146f5.html
Box2D for Android NDK
http://www.box2d.org/forum/viewtopic.php?f=5&t=3355&start=10

google group


http://groups.google.com/group/android-ndk/browse_thread/thread/10f2e02c5d6857cb?pli=1

android的skia本身已经不错了，