android 2d物理引擎-Box2d

转载http://rayleung.iteye.com/blog/439056

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：

Java代码

packagecom.ray.test;
importorg.jbox2d.collision.AABB;
importorg.jbox2d.collision.CircleDef;
importorg.jbox2d.collision.PolygonDef;
importorg.jbox2d.common.Vec2;
importorg.jbox2d.dynamics.Body;
importorg.jbox2d.dynamics.BodyDef;
importorg.jbox2d.dynamics.World;
importandroid.app.Activity;
importandroid.content.Context;
importandroid.graphics.Canvas;
importandroid.graphics.Color;
importandroid.graphics.Paint;
importandroid.os.Bundle;
importandroid.os.Handler;
importandroid.view.View;
importandroid.view.Window;
importandroid.view.WindowManager;
publicclassMyBox2dextendsActivity{
privatefinalstaticintRATE=10;//屏幕到现实世界的比例10px：1m;
privateAABBworldAABB;//创建一个管理碰撞的世界
privateWorldworld;
privatefloattimeStep=1/60;//模拟的的频率
privateintiterations=10;//迭代越大，模拟约精确，但性能越低
privateBodybody,body2,body3;
privateMyViewmyView;
privateHandlermHandler;
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
worldAABB=newAABB();
//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
Vec2gravity=newVec2(0.0f,10.0f);
booleandoSleep=true;
world=newWorld(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=newMyView(this);
setContentView(myView);
mHandler=newHandler();
mHandler.post(update);
}
privateRunnableupdate=newRunnable(){
publicvoidrun(){
world.step(timeStep,iterations);//开始模拟
Vec2position=body.getPosition();
Vec2position1=body2.getPosition();
Vec2position2=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);
}
};
publicvoidcreateBox(floatx,floaty,floathalf_width,floathalf_height,
booleanisStatic){
PolygonDefshape=newPolygonDef();
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);
BodyDefbodyDef=newBodyDef();
bodyDef.position.set(x/RATE,y/RATE);
Bodybody1=world.createBody(bodyDef);
body1.createShape(shape);
body1.setMassFromShapes();
}
publicvoidcreateCircle(floatx,floaty,floatradius){
CircleDefshape=newCircleDef();
shape.density=7;
shape.friction=0.2f;
shape.radius=radius/RATE;
BodyDefbodyDef=newBodyDef();
bodyDef.position.set(x/RATE,y/RATE);
body2=world.createBody(bodyDef);
body2.createShape(shape);
body2.setMassFromShapes();
}
publicvoidcreateCircle1(floatx,floaty,floatradius){
CircleDefshape=newCircleDef();
shape.density=7;
shape.friction=0.2f;
shape.radius=radius/RATE;
BodyDefbodyDef=newBodyDef();
bodyDef.position.set(x/RATE,y/RATE);
body3=world.createBody(bodyDef);
body3.createShape(shape);
body3.setMassFromShapes();
}
publicvoidcreateBox1(floatx,floaty,floathalf_width,floathalf_height,
booleanisStatic){
PolygonDefshape=newPolygonDef();
if(isStatic){shape.density=0;}
else{shape.density=2.0f;}
shape.friction=0.3f;
shape.setAsBox(half_width/RATE,half_height/RATE);
BodyDefbodyDef=newBodyDef();
bodyDef.position.set(x/RATE,y/RATE);
body=world.createBody(bodyDef);
body.createShape(shape);
body.setMassFromShapes();
}
classMyViewextendsView{
Canvascanvas;
publicfloatx=160,y=150;
publicfloatx1=160,y1=100;
publicfloatx2=150,y2=60;
publicMyView(Contextcontext){
super(context);
}
publicvoiddrawBox(floatx,floaty){
PaintmPaint=newPaint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.RED);
canvas.drawRect(x-160,y-10,x+160,y+10,mPaint);
}
publicvoiddrawGround(){
PaintmPaint=newPaint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.BLUE);
canvas.drawRect(0,460,320,480,mPaint);
}
publicvoiddrawCircle(floatx1,floaty1){
PaintmPaint=newPaint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.GREEN);
canvas.drawCircle(x1,y1,10,mPaint);
}
publicvoidupdate(){
postInvalidate();
}
protectedvoidonDraw(Canvascanvas){
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/ 附件也有

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