libgdx封装了Box2D物理引擎，通过这个引擎能够模拟物理现实，使设计出的游戏更具有真实感。
libgdx中，Box2d程序的大概过程：
1. 创建物理世界world，并设置重力加速度。
2. 创建正交相机，并设置其宽高。Box2d中使用物理世界中米作为单位，而不是图像中的像素，通常设一个比值，这里为了方便，直接设置为10。
3. 创建世界中的动态物体（一般是方块、圆环或其他形状物体）和静态物体（主要指地面、墙壁等）。
4. 在渲染函数中添加world时间布，并利用DebugRenderer将添加的物体绘制出来即可。
具体代码实例：
1 package com.fxb.newtest; 2 3 import com.badlogic.gdx.ApplicationAdapter; 4 import com.badlogic.gdx.Gdx; 5 import com.badlogic.gdx.graphics.GL10; 6 import com.badlogic.gdx.graphics.OrthographicCamera; 7 import com.badlogic.gdx.graphics.glutils.ShapeRenderer; 8 import com.badlogic.gdx.math.Vector2; 9 import com.badlogic.gdx.physics.box2d.Body; 10 import com.badlogic.gdx.physics.box2d.BodyDef; 11 import com.badlogic.gdx.physics.box2d.Box2DDebugRenderer; 12 import com.badlogic.gdx.physics.box2d.CircleShape; 13 import com.badlogic.gdx.physics.box2d.Fixture; 14 import com.badlogic.gdx.physics.box2d.FixtureDef; 15 import com.badlogic.gdx.physics.box2d.PolygonShape; 16 import com.badlogic.gdx.physics.box2d.World; 17 import com.badlogic.gdx.physics.box2d.BodyDef.BodyType; 18 19 public class Lib018_Box2d extends ApplicationAdapter{ 20 21 World world; 22 OrthographicCamera camera; 23 Box2DDebugRenderer debugRenderer; 24 ShapeRenderer rend; 25 26 @Override 27 public void create() { 28 // TODO Auto-generated method stub 29 super.create(); 30 31 world = new World( new Vector2( 0, -10f ), true ); 32 debugRenderer =new Box2DDebugRenderer(); 33 34 camera = new OrthographicCamera(); 35 camera.setToOrtho( false, Gdx.graphics.getWidth()/10, Gdx.graphics.getHeight()/10 ); 36 37 38 ////create the body of box 39 BodyDef boxBodyDef = new BodyDef(); 40 boxBodyDef.type = BodyType.DynamicBody; 41 //boxBodyDef.position.x = -24 + (float)(Math.random() * 48); 42 //boxBodyDef.position.y = 10 + (float)(Math.random() * 100); 43 boxBodyDef.position.set( 40, 50 ); 44 Body boxBody = world.createBody(boxBodyDef); 45 46 PolygonShape boxPoly = new PolygonShape(); 47 boxPoly.setAsBox(2, 1); 48 boxBody.createFixture(boxPoly, 1); 49 boxPoly.dispose(); 50 51 52 /////create the body of circle 53 BodyDef bodyDef = new BodyDef(); 54 bodyDef.type = BodyType.DynamicBody; 55 bodyDef.position.set( 60, 100 ); 56 Body bodyCircle = world.createBody( bodyDef ); 57 58 CircleShape circle = new CircleShape(); 59 circle.setRadius( 2 ); 60 FixtureDef fixtureDef = new FixtureDef(); 61 fixtureDef.shape = circle; 62 fixtureDef.density = 1f; 63 fixtureDef.friction = 0.4f; 64 //fixtureDef.restitution = 0.6f; 65 66 bodyCircle.createFixture( fixtureDef ); 67 circle.dispose(); 68 69 70 71 /////create the body of ground, static body, can't move 72 BodyDef groundBodyDef = new BodyDef(); 73 groundBodyDef.type = BodyType.StaticBody; 74 groundBodyDef.angle = (float)Math.PI*15/180; 75 groundBodyDef.position.set( 0, 0 ); 76 Body groundBody = world.createBody( groundBodyDef ); 77 78 PolygonShape groundBox = new PolygonShape(); 79 groundBox.setAsBox( camera.viewportWidth+5, 0.5f ); 80 groundBody.createFixture( groundBox, 0.0f ); 81 groundBox.dispose(); 82 83 } 84 85 @Override 86 public void render() { 87 // TODO Auto-generated method stub 88 super.render(); 89 //Gdx.gl.glClearColor( 1, 1, 1, 0.2f ); 90 Gdx.gl.glClear( GL10.GL_COLOR_BUFFER_BIT ); 91 92 world.step( Gdx.graphics.getDeltaTime(), 6, 2 ); 93 camera.update(); 94 95 debugRenderer.render( world, camera.combined ); 96 97 } 98 99 @Override 100 public void dispose() { 101 // TODO Auto-generated method stub 102 debugRenderer.dispose(); 103 world.dispose(); 104 super.dispose(); 105 } 106 107 }
运行结果：
程序中，添加了方块、圆环和地面三个物体，前两个为动态，地面为静态，让地面倾斜15度。
方块和圆环从高空下落到斜坡时，就向下滑动，与我们平常生活常识相吻合。