LibGdx--Box2d中元件与刚体重合

这里的元件暂且为图片，这里分两种情况：

1.知道图片的position，要绘制一个刚体与图片重合

2.知道刚体的position，要绘制一个图片与刚体重合

将单位换算的代码做一下封装

package com.joye3g.box2d.util;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.math.Vector2;

public class Transform {
	/**
	 * @param x_px				图片所在x坐标
	 * @param y_px				图片所在y坐标
	 * @param width_px			图片宽度
	 * @param height_px			图片高度
	 * @param scale				缩放比例
	 * @return					（x,y）直接设置为body的position可使body与图片重合
	 */
	public static Vector2 ptm(float x_px, float y_px, float width_px, float height_px, float scale){
		float screenWidth = Gdx.graphics.getWidth();
		float screenHeight = Gdx.graphics.getHeight();
		Vector2 vector2 = new Vector2();
		vector2.x = -(screenWidth - x_px * 2 - width_px) / scale / 2;
		vector2.y = -(screenHeight - y_px * 2 - height_px) / scale / 2;
		return vector2;
	}

	/**
	 * @param x_m				body所在x坐标
	 * @param y_m				body所在y坐标
	 * @param wh				(x,y)body的宽高
	 * @param scale				缩放比例
	 * @return					（x,y）直接设置为图片的position可使图片与body重合
	 */
	public static Vector2 mtp(float x_m, float y_m, Vector2 wh, float scale){
		float screenWidth = Gdx.graphics.getWidth();
		float screenHeight = Gdx.graphics.getHeight();
		Vector2 vector2 = new Vector2();
		vector2.x = x_m * scale + screenWidth / 2 - wh.x * scale;
		vector2.y = y_m * scale + screenHeight / 2 - wh.y * scale;
		return vector2;
	}
}

 

Fender.png图片，放到Android工程下的assets文件下

 

package com.joye3g.box2d;

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
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.BodyDef.BodyType;
import com.badlogic.gdx.physics.box2d.Box2DDebugRenderer;
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.scenes.scene2d.Stage;
import com.badlogic.gdx.scenes.scene2d.ui.Image;
import com.joye3g.box2d.util.Transform;

public class Box2dDemo implements ApplicationListener {
	private static final float PXTM = 30;
	private OrthographicCamera camera;
	private Box2DDebugRenderer renderer;
	private World world;
	private Stage stage;

	@Override
	public void create() {		
		float w = Gdx.graphics.getWidth();
		float h = Gdx.graphics.getHeight();

		float cameraWidth = w / PXTM;
		float cameraHeight = h / PXTM;
		camera = new OrthographicCamera(cameraWidth, cameraHeight);
		renderer = new Box2DDebugRenderer();

		stage = new Stage(w, h, false);
		
		
		//知道body的position，绘制图片与body重合
//		initBodyForImage();
		
		//知道图片的position,绘制body与图片重合
		initImageForBody();
	}

	private void initImageForBody() {
		Texture texture = new Texture(Gdx.files.internal("Fender.png"));
		Image image = new Image(texture);
		//一个点，表示图片的position,坐标为（200，200）
		Vector2 vector2 = new Vector2(200f, 200f);
		image.setPosition(vector2.x, vector2.y);
		stage.addActor(image);
		
		world = new World(new Vector2(0f, 0f), true);
		BodyDef def = new BodyDef();
		def.type = BodyType.StaticBody;
		//将图片的position转换为物理世界中的点并做一些处理，使绘制出来的body的左下角位置与图片的左下角位置重合
		Vector2 vector3 = Transform.ptm(vector2.x, vector2.y, image.getWidth(), image.getHeight(), PXTM);
		def.position.set(vector3.x, vector3.y);
		Body body = world.createBody(def);
		PolygonShape shape = new PolygonShape();
		//将图形的宽高稍微加大一点，方便看到效果
		shape.setAsBox(image.getWidth() / PXTM / 2 + 0.1f, image.getHeight() / PXTM / 2 + 0.1f);
		FixtureDef def2 = new FixtureDef();
		def2.shape = shape;
		body.createFixture(def2);
	}

	private void initBodyForImage() {
		Texture texture = new Texture(Gdx.files.internal("Fender.png"));
		Image image = new Image(texture);
		
		world = new World(new Vector2(0f, 0f), true);
		BodyDef def = new BodyDef();
		def.type = BodyType.StaticBody;
		def.position.set(0f, 0f);
		Body body = world.createBody(def);
		PolygonShape shape = new PolygonShape();
		Vector2 vector3 = new Vector2(image.getWidth() / 2 / PXTM, image.getHeight() / 2 / PXTM);
		shape.setAsBox(vector3.x + 0.1f, vector3.y + 0.1f);
		FixtureDef def2 = new FixtureDef();
		def2.shape = shape;
		body.createFixture(def2);
		
		Vector2 vector2 = Transform.mtp(body.getPosition().x, body.getPosition().y, vector3, PXTM);
		image.setPosition(vector2.x, vector2.y);
		stage.addActor(image);
	}

	@Override
	public void dispose() {
	}

	@Override
	public void render() {		
		Gdx.gl.glClearColor(1, 1, 1, 1);
		Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
		renderer.render(world, camera.combined);
		stage.draw();
	}

	@Override
	public void resize(int width, int height) {
	}

	@Override
	public void pause() {
	}

	@Override
	public void resume() {
	}
}

 

运行结果：