xeoshow: rope hanging from 2 boxes with ball falling on rope

package net.dermetfan.someLibgdxTests.screens;

import net.dermetfan.libgdx.graphics.FixtureSprite;
import net.dermetfan.someLibgdxTests.Assets;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Screen;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
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.CircleShape;
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.joints.RevoluteJointDef;

public class Box2DRopeTest implements Screen {

    private SpriteBatch batch;
    private Box2DDebugRenderer debugRenderer;
    private OrthographicCamera camera;
    private World world;

    @Override
    public void render(float delta) {
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

        world.step(1 / 60f, 8, 20);

        camera.update();
        batch.setProjectionMatrix(camera.combined);
        batch.begin();
        FixtureSprite.draw(batch, world);
        batch.end();

        debugRenderer.render(world, camera.combined);
    }

    @Override
    public void resize(int width, int height) {
        camera.viewportWidth = width / 25;
        camera.viewportHeight = height / 25;
    }

    @Override
    public void show() {
        batch = new SpriteBatch();
        debugRenderer = new Box2DDebugRenderer();
        camera = new OrthographicCamera();
        world = new World(new Vector2(0, -9.81f), true);

        BodyDef bodyDef = new BodyDef();
        FixtureDef fixtureDef = new FixtureDef();

        // box (the rope will hang from this)
        bodyDef.type = BodyType.StaticBody;
        bodyDef.position.y = 7;
        PolygonShape boxShape = new PolygonShape();
        boxShape.setAsBox(.5f, .5f);
        Body box = world.createBody(bodyDef);
        box.createFixture(boxShape, 0);

        // box (the rope will hang from this as well)
        bodyDef.type = BodyType.StaticBody;
        bodyDef.position.set(4, 8);
        PolygonShape boxShape2 = new PolygonShape();
        boxShape2.setAsBox(.1f, .1f);
        Body box2 = world.createBody(bodyDef);
        box2.createFixture(boxShape2, 0);
        boxShape2.dispose();

        // rope
        short segments = 20;
        float segWidth = .1f, segHeight = .3f;

        // segment definitions
        bodyDef.type = BodyType.DynamicBody;
        bodyDef.position.y = 6;
        PolygonShape segmentShape = new PolygonShape();
        segmentShape.setAsBox(segWidth / 2, segHeight / 2);
        fixtureDef.shape = segmentShape;
        fixtureDef.density = 1;
        fixtureDef.friction = .3f;
        fixtureDef.restitution = .05f;

        // revolute joint definitions
        RevoluteJointDef ropeDef = new RevoluteJointDef();
        ropeDef.localAnchorA.set(0, -segHeight / 2); // top
        ropeDef.localAnchorB.set(0, segHeight / 2); // bottom

        FixtureSprite segmentSprite = new FixtureSprite(Assets.japanischeFlagge);

        // first segment
        Body lastSegment = world.createBody(bodyDef);
        lastSegment.createFixture(fixtureDef).setUserData(segmentSprite);
        ropeDef.bodyA = box;
        ropeDef.bodyB = lastSegment;
        float oldLocalAnchorAY = ropeDef.localAnchorA.y;
        ropeDef.localAnchorA.y = -.5f; // set to the bottom of the box
        world.createJoint(ropeDef);
        ropeDef.localAnchorA.y = oldLocalAnchorAY;

        // other segments
        for(int s = 1; s < segments; s++) {
            bodyDef.position.y -= segHeight; // position the segments one under another
            ropeDef.bodyA = lastSegment;
            ropeDef.bodyB = world.createBody(bodyDef);
            ropeDef.bodyB.createFixture(fixtureDef).setUserData(segmentSprite);
            world.createJoint(ropeDef);
            lastSegment = ropeDef.bodyB;
        }

        segmentShape.dispose();

        // last joint
        ropeDef.bodyA = lastSegment;
        ropeDef.bodyB = box2;
        ropeDef.localAnchorB.y = -.1f;
        world.createJoint(ropeDef);

        // ball (will fall on the rope)
        bodyDef.type = BodyType.DynamicBody;
        bodyDef.position.set(1.5f, 10);
        CircleShape ballShape = new CircleShape();
        ballShape.setRadius(.25f);
        fixtureDef.shape = ballShape;
        fixtureDef.restitution = .5f;
        fixtureDef.density = 3;
        fixtureDef.friction = .3f;
        world.createBody(bodyDef).createFixture(fixtureDef).setUserData(new FixtureSprite(Assets.ball));
        ballShape.dispose();
    }

    @Override
    public void hide() {
        dispose();
    }

    @Override
    public void pause() {
    }

    @Override
    public void resume() {
    }

    @Override
    public void dispose() {
        batch.dispose();
        debugRenderer.dispose();
    }

}