JBox2D For Android - hello box2d

鉴于最近工作涉及JBox2D，打算围绕testbed的sample来做些细致的了解。也希望自己学习的同时跟大家探讨。

虽然box2d的手册已经详细的描述了hello box2d的代码，本篇也主要是简单用android实现，没有绘制部分，但是很清楚的描述了box2d运行的基本情况。

</pre><pre name="code" class="java"> 

 /********************************/
 /*Box2D v2.2.0 User Manual 文中代码的android实现版本*/
 /*本例调用JBox2d4Android_2.1.2.jar*/
 /*下载<span style="background-color: rgb(255, 255, 255); ">JBox2d4Android_2.1.2.jar </span> http://download.csdn.net/detail/z1074971432/3831279*/
 /********************************/
 import org.jbox2d.collision.shapes.PolygonShape;
 import org.jbox2d.common.Vec2;
 import org.jbox2d.dynamics.Body;
 import org.jbox2d.dynamics.BodyDef;
 import org.jbox2d.dynamics.BodyType;
 import org.jbox2d.dynamics.FixtureDef;
 import org.jbox2d.dynamics.World;

 import android.app.Activity;
 import android.content.Context;
 import android.os.Bundle;
 import android.view.View;

 public class Box2d_lesson1_hellobox2dActivity extends Activity {
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(new helloBox2dView(this));
     }

     class helloBox2dView extends View {

         public helloBox2dView(Context context) {
             super(context);
             World world;
             /** Creating a World */
             {
                 Vec2 gravity = new Vec2(0, -10f);
                 boolean dosleep = true;
                 world = new World(gravity, dosleep);
             }
             /** Creating a Ground Box */
             {
             // Bodies are built using the following steps:
                 // Step 1. Define a body with position, damping, etc.
                 BodyDef groundBodyDef = new BodyDef();
                 groundBodyDef.position.set(0.0f, 1.0f);
                 // Step 2. Use the world object to create the body.
                 Body groundBody = world.createBody(groundBodyDef);
                 // Step 3. Define fixtures with a shape, friction, density, etc.
                 PolygonShape groundBox = new PolygonShape();
                 groundBox.setAsBox(50.0f, 1.0f);
                 // Step 4. Create fixtures on the body.
                 groundBody.createFixture(groundBox, 0.0f);
             }
             /** Creating a Dynamic Body */
             Body body;
             {
                 BodyDef bodyDef = new BodyDef();
                 bodyDef.type = BodyType.DYNAMIC;
                 bodyDef.position.set(0.0f, 4.0f);
                 body = world.createBody(bodyDef);


                 PolygonShape dynamicBox = new PolygonShape();
                 dynamicBox.setAsBox(1.0f, 1.0f);

                 FixtureDef fixtureDef = new FixtureDef();
                 fixtureDef.shape = dynamicBox;
                 fixtureDef.density = 1.0f;
                 fixtureDef.friction = 0.3f;

                 body.createFixture(fixtureDef);

             }

             /** Simulating the World (of Box2D) */
             {
                 float timeStep = 1.0f / 60.0f;
                 int velocityIterations = 6;
                 int positionIterations = 2;

                 for (int i = 0; i < 60; ++i)
                 {
                     world.step(timeStep, velocityIterations, positionIterations);
                     Vec2 position = body.getPosition();
                     float angle = body.getAngle();
                     System.out.printf("%4.2f %4.2f %4.2f\n", position.x, position.y, angle);
                 }


             }

         }

     }