libgdx之RevoluteJointDef关节

原文链接http://blog.csdn.net/cng1991/article/details/7307881

最近在看libgdx的box2d相关的知识。网上介绍libgdx是通过jni封装了box2d的。

今天看到了RevoluteJointDef关节。RevoluteJointDef关节的作用就是将两个物体用线连起来，达到两个物体运动相互影响的效果。

先贴出代码

package com.cng;

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.InputProcessor;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.math.Vector2;
import com.badlogic.gdx.math.Vector3;
import com.badlogic.gdx.physics.box2d.Body;
import com.badlogic.gdx.physics.box2d.BodyDef;
import com.badlogic.gdx.physics.box2d.BodyDef.BodyType;
import com.badlogic.gdx.physics.box2d.Box2DDebugRenderer;
import com.badlogic.gdx.physics.box2d.Fixture;
import com.badlogic.gdx.physics.box2d.QueryCallback;
import com.badlogic.gdx.physics.box2d.World;
import com.badlogic.gdx.physics.box2d.joints.MouseJoint;
import com.badlogic.gdx.physics.box2d.joints.MouseJointDef;

public abstract class BoxTest implements InputProcessor,ApplicationListener
{

	OrthographicCamera camera;
	Box2DDebugRenderer renderer;
	MouseJoint mouseJoint;
	World world;
	Body grounpBody;
	Body hitBody;
	protected abstract void createWorld(World world);
	
	
	Vector2 tmp=new Vector2();
	@Override
	public void create()
	{
		camera=new OrthographicCamera(48, 32);
		camera.position.set(0, 15, 0);
		
		renderer=new Box2DDebugRenderer();
		world=new World(new Vector2(0,-10), true);
		createWorld(world);
		BodyDef bodyDef=new BodyDef();
		grounpBody=world.createBody(bodyDef);
		Gdx.input.setInputProcessor(this);
	}

	@Override
	public void dispose()
	{
		world.dispose();
		renderer.dispose();
		
		world=null;
		renderer=null;
		hitBody=null;
		mouseJoint=null;
		
		
	}

	@Override
	public void pause()
	{
		
	}

	@Override
	public void render()
	{
		GL10 gl=Gdx.graphics.getGL10();
		gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
		camera.update();
		camera.apply(gl);
		world.step(Gdx.graphics.getDeltaTime(), 3, 3);
		renderer.render(world, camera.combined);
	}

	@Override
	public void resize(int arg0, int arg1)
	{
		
	}

	@Override
	public void resume()
	{
		
	}

	@Override
	public boolean keyDown(int arg0)
	{
		return false;
	}

	@Override
	public boolean keyTyped(char arg0)
	{
		return false;
	}

	@Override
	public boolean keyUp(int arg0)
	{
		return false;
	}

	@Override
	public boolean scrolled(int arg0)
	{
		return false;
	}

	Vector3 testPoint=new Vector3();
	QueryCallback callback=new QueryCallback()
	{
		
		@Override
		public boolean reportFixture(Fixture fixture)
		{
			if(fixture.testPoint(testPoint.x, testPoint.y))
			{
				hitBody=fixture.getBody();
				return false;
			}
			else 
			{
				return true;
			}
			
		}
	};
	@Override
	public boolean touchDown(int x, int y, int arg2, int arg3)
	{
		hitBody=null;
		camera.unproject(testPoint.set(x, y, 0));
		world.QueryAABB(callback, testPoint.x-0.0001f, testPoint.y-0.0001f, testPoint.x+0.0001f, testPoint.y+0.0001f);
		if(hitBody==grounpBody) hitBody=null;
		if(hitBody!=null&&hitBody.getType()==BodyType.KinematicBody)
		{
			return false;
		}
		if(hitBody!=null)
		{
			MouseJointDef def=new MouseJointDef();
			def.bodyA=grounpBody;
			def.bodyB=hitBody;
			def.collideConnected=true;
			def.target.set(testPoint.x, testPoint.y);
			def.maxForce=100*hitBody.getMass();
			mouseJoint=(MouseJoint) world.createJoint(def);
			hitBody.setAwake(true);
		}
		return false;
	}

	Vector2 target=new Vector2();
	@Override
	public boolean touchDragged(int x, int y, int arg2)
	{
		if(mouseJoint!=null)
		{
			camera.unproject(testPoint.set(x, y, 0));
			mouseJoint.setTarget(target.set(testPoint.x,testPoint.y));
		}
		return false;
	}

	@Override
	public boolean touchMoved(int arg0, int arg1)
	{
		return false;
	}

	@Override
	public boolean touchUp(int arg0, int arg1, int arg2, int arg3)
	{
		if(mouseJoint!=null)
		{
			world.destroyJoint(mouseJoint);
			mouseJoint=null;
		}
		return false;
	}
}

package com.cng;





import android.os.Bundle;
import com.badlogic.gdx.backends.android.AndroidApplication;
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.EdgeShape;
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;
import com.badlogic.gdx.physics.box2d.joints.RevoluteJointDef;




public class MyGameActivity extends AndroidApplication {
	 
	class MyGameListen  extends BoxTest
	{

		
		@Override
		protected void createWorld(World world)
		{
			Body ground;
			{
				BodyDef bodyDef=new BodyDef();//新建物理对象
				ground=world.createBody(bodyDef);

				
				EdgeShape shape=new EdgeShape();//新建物理对象的显示图形
				shape.set(new Vector2(-40, 0), new Vector2(40, 0));
				
				ground.createFixture(shape, 0.0f);//使物理对象有外表，即可看到的图形
			}
			{
				Body preBody=ground;//定义关节前的物体
				PolygonShape shape=new PolygonShape();
				shape.setAsBox(0.5f, 0.2f);
				RevoluteJointDef rj=null;
				
				for(int i=0;i<30;i++)
				{
					BodyDef def=new BodyDef();
					def.type=BodyType.DynamicBody;
					def.position.set(0.5f+i, 25f);
					Body body=world.createBody(def);//定义关节后的物体
					
					FixtureDef fd=new FixtureDef();
					fd.shape=shape;
					fd.friction=0.2f;
					fd.density=20.0f;
					body.createFixture(fd);
					
					Vector2 anchor=new Vector2(i,25);
					rj=new RevoluteJointDef();
					rj.initialize(preBody, body, anchor);
					preBody=body;
					world.createJoint(rj);
				}
				
				
			}
		}
	}
	
	
	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		initialize(new MyGameListen(), false);
	}
	
}

我大概也就只能解释那么多了。。。能力有限。等学得在深入点，我再修改下，解释的更详细点。