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：

  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。