如何将图像背景设置为jbox2d多边形

Question

我正在尝试在Android上开发一个游戏，在BodyDef上使用名为“Jbox2DTestbed”的jbox2d示例我想从我的资源设置图像位图，但我的代码不起作用。 varyfriction示例的原始外观如下：

    package com.tszy.jbox2d.testbed.tests;

import org.jbox2d.collision.shapes.PolygonShape;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.Body;
import org.jbox2d.dynamics.BodyDef;
import org.jbox2d.dynamics.BodyType;
import org.jbox2d.dynamics.FixtureDef;


import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.view.SurfaceHolder;

import com.tszy.jbox2d.testbed.R;


import com.tszy.jbox2d.testbed.framework.TestbedView;

public class VaryingFriction extends TestbedView {

    ObjectHolder objectHolder;
    SurfaceHolder holder;
    Bitmap image;
    Matrix matrix;

    public VaryingFriction(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void initTest() {
        // TODO Auto-generated method stub
        matrix=new Matrix();
        image = BitmapFactory.decodeResource(getResources(),
                R.drawable.star);
        holder=super.getHolder();

        {
            BodyDef bd = new BodyDef();
            Body ground = getWorld().createBody(bd);

            PolygonShape shape = new PolygonShape();
            //shape.setAsEdge(new Vec2(-40.0f, 0.0f),new Vec2(40.0f, 0.0f));
            shape.setAsEdge(new Vec2(-40.0f, 0.0f),new Vec2(40.0f, 0.0f));
            ground.createFixture(shape, 0.0f);
        }

        {
            PolygonShape shape = new PolygonShape();
            shape.setAsBox(13.0f, 0.25f);

            BodyDef bd = new BodyDef();
            bd.position.set(-4.0f, 22.0f);
            bd.angle = -0.25f;

            Body ground = getWorld().createBody(bd);
            ground.createFixture(shape, 0.0f);
        }

        {
            PolygonShape shape = new PolygonShape();
            shape.setAsBox(0.25f, 1.0f);

            BodyDef bd = new BodyDef();
            bd.position.set(10.5f, 19.0f);

            Body ground = getWorld().createBody(bd);
            ground.createFixture(shape, 0.0f);
        }

        {
            PolygonShape shape = new PolygonShape();
            shape.setAsBox(13.0f, 0.25f);

            BodyDef bd = new BodyDef();
            bd.position.set(4.0f, 14.0f);
            bd.angle = 0.25f;

            Body ground = getWorld().createBody(bd);
            ground.createFixture(shape, 0.0f);
        }

        {
            PolygonShape shape = new PolygonShape();
            shape.setAsBox(0.25f, 1.0f);

            BodyDef bd = new BodyDef();
            bd.position.set(-10.5f, 11.0f);

            Body ground = getWorld().createBody(bd);
            ground.createFixture(shape, 0.0f);
        }

        {
            PolygonShape shape = new PolygonShape();
            shape.setAsBox(13.0f, 0.25f);

            BodyDef bd = new BodyDef();
            bd.position.set(-4.0f, 6.0f);
            bd.angle = -0.25f;

            Body ground = getWorld().createBody(bd);
            ground.createFixture(shape, 0.0f);
        }

        {
            PolygonShape shape = new PolygonShape();
            shape.setAsBox(0.5f, 0.5f);

            FixtureDef fd = new FixtureDef();
            fd.shape = shape;
            fd.density = 25.0f;

            float friction[] = {0.75f, 0.5f, 0.35f, 0.1f, 0.0f};
            CommonDefs commondefs = new CommonDefs();

            commondefs.initialize(getContext());




            matrix=new Matrix();
            Canvas c=null;

            for (int i = 0; i < 5; ++i)
            {
                BodyDef bd = new BodyDef();
                bd.type = BodyType.DYNAMIC;
                bd.position.set(-15.0f + 4.0f * i, 28.0f);
                Body body = getWorld().createBody(bd);


                /////////////-----------the code i added---------------------////////////////////////////////////
                c=holder.lockCanvas();
                //** trying to draw an image upon this body**//
                drawCircle(c, body);
                holder.unlockCanvasAndPost(c);
                ///////////////////////////////////////////////////////////////////


                fd.friction = friction[i];
                body.createFixture(fd);
                getWorld().setAutoClearForces(false);   


            }
      }

    }


    private void drawCircle(Canvas c, Body body)
    { 

        matrix.reset(); 
        matrix.postRotate(body.getAngle()/3.14f*180f); 
        matrix.preTranslate(-image.getWidth()>>>1, -image.getHeight()>>>1);
        matrix.postTranslate(body.getPosition().x, body.getPosition().y); 
        c.drawBitmap(image, matrix, null);
    }

    @Override
    public String getName() {
        // TODO Auto-generated method stub
        return "Varying Friction";
    }


}