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"> 

1. /********************************/  
2. /*Box2D v2.2.0 User Manual 文中代码的android实现版本*/  
3. /*本例调用JBox2d4Android_2.1.2.jar*/  
4. /*下载<span style="background-color: rgb(255, 255, 255); ">JBox2d4Android_2.1.2.jar </span> http://download.csdn.net/detail/z1074971432/3831279*/  
5. /********************************/  
6. import org.jbox2d.collision.shapes.PolygonShape;  
7. import org.jbox2d.common.Vec2;  
8. import org.jbox2d.dynamics.Body;  
9. import org.jbox2d.dynamics.BodyDef;  
10. import org.jbox2d.dynamics.BodyType;  
11. import org.jbox2d.dynamics.FixtureDef;  
12. import org.jbox2d.dynamics.World;  
13.   
14. import android.app.Activity;  
15. import android.content.Context;  
16. import android.os.Bundle;  
17. import android.view.View;  
18.   
19. public class Box2d_lesson1_hellobox2dActivity extends Activity {  
20.     /** Called when the activity is first created. */  
21.     @Override  
22.     public void onCreate(Bundle savedInstanceState) {  
23.         super.onCreate(savedInstanceState);  
24.         setContentView(new helloBox2dView(this));  
25.     }  
26.   
27.     class helloBox2dView extends View {  
28.   
29.         public helloBox2dView(Context context) {  
30.             super(context);  
31.             World world;  
32.             /** Creating a World */  
33.             {  
34.                 Vec2 gravity = new Vec2(0, -10f);  
35.                 boolean dosleep = true;  
36.                 world = new World(gravity, dosleep);  
37.             }  
38.             /** Creating a Ground Box */  
39.             {  
40.             // Bodies are built using the following steps:  
41.                 // Step 1. Define a body with position, damping, etc.  
42.                 BodyDef groundBodyDef = new BodyDef();  
43.                 groundBodyDef.position.set(0.0f, 1.0f);  
44.                 // Step 2. Use the world object to create the body.  
45.                 Body groundBody = world.createBody(groundBodyDef);  
46.                 // Step 3. Define fixtures with a shape, friction, density, etc.  
47.                 PolygonShape groundBox = new PolygonShape();  
48.                 groundBox.setAsBox(50.0f, 1.0f);  
49.                 // Step 4. Create fixtures on the body.  
50.                 groundBody.createFixture(groundBox, 0.0f);  
51.             }  
52.             /** Creating a Dynamic Body */  
53.             Body body;  
54.             {  
55.                 BodyDef bodyDef = new BodyDef();  
56.                 bodyDef.type = BodyType.DYNAMIC;  
57.                 bodyDef.position.set(0.0f, 4.0f);  
58.                 body = world.createBody(bodyDef);  
59.                   
60.                   
61.                 PolygonShape dynamicBox = new PolygonShape();  
62.                 dynamicBox.setAsBox(1.0f, 1.0f);  
63.                   
64.                 FixtureDef fixtureDef = new FixtureDef();  
65.                 fixtureDef.shape = dynamicBox;  
66.                 fixtureDef.density = 1.0f;  
67.                 fixtureDef.friction = 0.3f;  
68.                   
69.                 body.createFixture(fixtureDef);  
70.                   
71.             }  
72.               
73.             /** Simulating the World (of Box2D) */  
74.             {  
75.                 float timeStep = 1.0f / 60.0f;  
76.                 int velocityIterations = 6;  
77.                 int positionIterations = 2;  
78.                   
79.                 for (int i = 0; i < 60; ++i)  
80.                 {  
81.                     world.step(timeStep, velocityIterations, positionIterations);  
82.                     Vec2 position = body.getPosition();  
83.                     float angle = body.getAngle();  
84.                     System.out.printf("%4.2f %4.2f %4.2f\n", position.x, position.y, angle);  
85.                 }  
86.                   
87.                   
88.             }  
89.               
90.         }  
91.   
92.     }