libgdx学习记录18——Box2d物理引擎

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：

 package com.fxb.newtest;

 import com.badlogic.gdx.ApplicationAdapter;
 import com.badlogic.gdx.Gdx;
 import com.badlogic.gdx.graphics.GL10;
 import com.badlogic.gdx.graphics.OrthographicCamera;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
 import com.badlogic.gdx.math.Vector2;
 import com.badlogic.gdx.physics.box2d.Body;
 import com.badlogic.gdx.physics.box2d.BodyDef;
 import com.badlogic.gdx.physics.box2d.Box2DDebugRenderer;
 import com.badlogic.gdx.physics.box2d.CircleShape;
 import com.badlogic.gdx.physics.box2d.Fixture;
 import com.badlogic.gdx.physics.box2d.FixtureDef;
 import com.badlogic.gdx.physics.box2d.PolygonShape;
 import com.badlogic.gdx.physics.box2d.World;
 import com.badlogic.gdx.physics.box2d.BodyDef.BodyType;

 public class Lib018_Box2d extends ApplicationAdapter{

     World world;
     OrthographicCamera camera;
     Box2DDebugRenderer debugRenderer;
     ShapeRenderer rend;

     @Override
     public void create() {
         // TODO Auto-generated method stub
         super.create();

         world = new World( new Vector2( 0, -10f ), true );
         debugRenderer =new Box2DDebugRenderer();

         camera = new OrthographicCamera();
         camera.setToOrtho( false, Gdx.graphics.getWidth()/10, Gdx.graphics.getHeight()/10 );

         ////create the body of box
         BodyDef boxBodyDef = new BodyDef();
         boxBodyDef.type = BodyType.DynamicBody;
         //boxBodyDef.position.x = -24 + (float)(Math.random() * 48);
         //boxBodyDef.position.y = 10 + (float)(Math.random() * 100);
         boxBodyDef.position.set( 40, 50 );
         Body boxBody = world.createBody(boxBodyDef);

         PolygonShape boxPoly = new PolygonShape();
         boxPoly.setAsBox(2, 1);
         boxBody.createFixture(boxPoly, 1);
         boxPoly.dispose();

         /////create the body of circle
         BodyDef bodyDef = new BodyDef();
         bodyDef.type = BodyType.DynamicBody;
         bodyDef.position.set( 60, 100 );
         Body bodyCircle = world.createBody( bodyDef );

         CircleShape circle = new CircleShape();
         circle.setRadius( 2 );
         FixtureDef fixtureDef = new FixtureDef();
         fixtureDef.shape = circle;
         fixtureDef.density = 1f;
         fixtureDef.friction = 0.4f;
         //fixtureDef.restitution = 0.6f;

         bodyCircle.createFixture( fixtureDef );
         circle.dispose();

         /////create the body of ground, static body, can't move
         BodyDef groundBodyDef = new BodyDef();
         groundBodyDef.type = BodyType.StaticBody;
         groundBodyDef.angle = (float)Math.PI*15/180;
         groundBodyDef.position.set( 0, 0 );
         Body groundBody = world.createBody( groundBodyDef );

         PolygonShape groundBox = new PolygonShape();
         groundBox.setAsBox( camera.viewportWidth+5, 0.5f );
         groundBody.createFixture( groundBox, 0.0f );
         groundBox.dispose();

     }

     @Override
     public void render() {
         // TODO Auto-generated method stub
         super.render();
         //Gdx.gl.glClearColor( 1, 1, 1, 0.2f );
         Gdx.gl.glClear( GL10.GL_COLOR_BUFFER_BIT );

         world.step( Gdx.graphics.getDeltaTime(), 6, 2 );
         camera.update();

         debugRenderer.render( world, camera.combined );

     }

     @Override
     public void dispose() {
         // TODO Auto-generated method stub
         debugRenderer.dispose();
         world.dispose();
         super.dispose();
     }

 }

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。