libgdx bind multiple part textures and stuff

Question

I am developing an off road game, and I am new to libgdx.

I made a car, with only 3 parts: chassis, rear & front wheel. I got a "Zoomable" camera bind with chassis, chassis connected to wheels with Wheel Joint.

Chassis works fine with texture but not wheels.

Here's the problems:

1. I can't figure out how to calculate the √(correct) vector2 of wheels to put it in the [Sprite.setPosition] method
2. How to make my car faster cause it never >94

Focus.java

public class Focus extends InputAdapter {
    private Body chassis, rearWheel, frontWheel;
    private WheelJoint leftAxis, rightAxis;
    private float speed = 90f;
    private Sprite spriteChassis, spriteRearWheel, spriteFrontWheel;
    private float xOffSet = 5f;
    private float yOffSet = -2f;
    private float rwOffSet = 0;
    private float fwOffSet = 0;

    private float rwOffSetY = 0;
    private float fwOffSetY = 0;


    public float getOffSetX(){ return xOffSet; }
    public float getOffSetY(){ return yOffSet; }

    public Focus(World world, FixtureDef chassisFixtureDef, FixtureDef wheelFixtureDef, float x, float y) {
        BodyDef bodyDef = new BodyDef();
        bodyDef.type = BodyDef.BodyType.DynamicBody;
        bodyDef.position.set(x,y);
        bodyDef.gravityScale = 1;
        float width = 5.333f;
        float height = 1.933f;


        BodyEditorLoader loader = new BodyEditorLoader(Gdx.files.internal("data/focus.json"));
        chassis = world.createBody(bodyDef);
        loader.attachFixture(chassis, "focus", chassisFixtureDef, width);
        String imgpath = loader.getImagePath("focus");
        chassis.createFixture(chassisFixtureDef);
        chassis.setGravityScale(1.2f);

        spriteChassis = new Sprite(new Texture(imgpath));
        spriteRearWheel = new Sprite(new Texture("tires.png"));
        spriteFrontWheel = new Sprite(new Texture("tires.png"));

        // Wheels
        CircleShape wheelShape = new CircleShape();
        wheelShape.setRadius(height / 6f);

        wheelFixtureDef.shape = wheelShape;

        rearWheel = world.createBody(bodyDef);
        rearWheel.createFixture(wheelFixtureDef);

        frontWheel = world.createBody(bodyDef);
        frontWheel.createFixture(wheelFixtureDef);


        // Axels
        WheelJointDef axisDef = new WheelJointDef();
        axisDef.bodyA = chassis;
        axisDef.bodyB = rearWheel;
        rwOffSet = wheelShape.getRadius()*3.3f;
        axisDef.localAnchorA.x = rwOffSet;
        rwOffSetY = height/10.5f;
        axisDef.localAnchorA.y = rwOffSetY;
        axisDef.frequencyHz = chassisFixtureDef.density;
        axisDef.localAxisA.set(Vector2.Y);
        axisDef.maxMotorTorque = chassisFixtureDef.density * 24.5f;

        leftAxis = (WheelJoint) world.createJoint(axisDef);

//        right
//        Axels
        WheelJointDef axisDef2 = new WheelJointDef();
        axisDef2.bodyA = chassis;
        axisDef2.bodyB = frontWheel;
        axisDef2.localAnchorA.set(width, 0);
        axisDef2.frequencyHz = chassisFixtureDef.density;
        axisDef2.localAxisA.set(Vector2.Y);
        fwOffSet = width-wheelShape.getRadius()*3.f;
        axisDef2.localAnchorA.x = fwOffSet;
        fwOffSetY = height/9f;
        axisDef.localAnchorA.y = fwOffSetY;
        axisDef2.maxMotorTorque = chassisFixtureDef.density * 24.5f;
        rightAxis = (WheelJoint) world.createJoint(axisDef2);

    }



    @Override
    public boolean keyDown(int keycode) {

        switch(keycode) {
            case Input.Keys.W:
                leftAxis.enableMotor(false);
                rightAxis.enableMotor(true);
                rightAxis.setMotorSpeed(-speed);
                break;
            case Input.Keys.S:
                leftAxis.enableMotor(false);

                rightAxis.enableMotor(true);
                rightAxis.setMotorSpeed(speed);
                break;
            case Input.Keys.SPACE:
                leftAxis.enableMotor(true);
                leftAxis.setMotorSpeed(0);

                rightAxis.enableMotor(true);
                rightAxis.setMotorSpeed(0);
                break;
        }
        return true;
    }

    @Override
    public boolean keyUp(int keycode) {
        switch(keycode) {

            case Input.Keys.SPACE:
            case Input.Keys.W:
            case Input.Keys.S:
                leftAxis.enableMotor(false);
                rightAxis.enableMotor(false);
                break;
        }
        return true;
    }

    public Sprite getSpriteChassis(){ return spriteChassis; }

    public Sprite getSpriteRearWheel() { return spriteRearWheel; }

    public Sprite getSpriteFrontWheel() { return spriteFrontWheel; }

    public Body getChassis() { return chassis; }

    public Body getFrontWheel() { return frontWheel; }

    public Body getRearWheel() { return rearWheel; }
}

SmallHill.java (Screen)

public class SmallHill implements Screen {


    private final float PIXELS_PER_METER = 15f;     // how many pixels to a meter
    private final float TIME_STEP = 1 / 60f;        // 60 fps
    private final float SPEED = 1 / 60f;            // speed constant
    private final float MIN_ZOOM = .25f;            // How far in should we be able to zoom
    private final float ANGULAR_MOMENTUM = .5f;
    private final int VELOCITY_ITERATIONS = 8;      // copied from box2d example
    private final int POSITION_ITERATIONS = 3;      // copied from box2d example

    private World world;
    private Box2DDebugRenderer debugRenderer;
    private OrthographicCamera camera;
    private Body ball;
    private Focus focus;


    private BitmapFont font;

    private SpriteBatch batch;      
    private Texture texture;


    @Override
    public void show() {
        batch = new SpriteBatch();
        font = new BitmapFont();
        font.setColor(Color.RED);


        world = new World(new Vector2(0, -9.81f), true);
        debugRenderer = new Box2DDebugRenderer();

        camera = new OrthographicCamera();
        camera.zoom = 1f;

        BodyDef bodyDef = new BodyDef();

        // Shape
        ChainShape groundShape = new ChainShape();
        groundShape.createChain(new Vector2[] {new Vector2(-1,24),new Vector2(0,14),new Vector2(25,14),new Vector2(50,10),new Vector2(100,5),new Vector2(150,12),new Vector2(155,10), new Vector2(200,22),new Vector2(225,22),new Vector2(226,22.15f),new Vector2(227,22),new Vector2(229,22.25f),new Vector2(350,22),new Vector2(385,24),new Vector2(389,25),new Vector2(390,24),new Vector2(395,25),new Vector2(398,24),new Vector2(400,25),new Vector2(401,48) });
        CircleShape ballShape = new CircleShape();
        ballShape.setRadius(1f);
        ballShape.setPosition(new Vector2(-10, 16));

        // Fixture

        FixtureDef fixtureDef = new FixtureDef();
        fixtureDef.shape = groundShape;
        fixtureDef.friction = .8f;
        fixtureDef.restitution = 0;
        world.createBody(bodyDef).createFixture(fixtureDef);

        fixtureDef.shape = ballShape;
        fixtureDef.friction = 0.9f;
        fixtureDef.restitution = .3f;
        fixtureDef.density = 3;
        bodyDef.type = BodyType.DynamicBody;

        fixtureDef.density = 5;
        fixtureDef.friction = .4f;
        fixtureDef.restitution = .1f;

        FixtureDef wheelFixtureDef = new FixtureDef();
        wheelFixtureDef.density = fixtureDef.density ;
        wheelFixtureDef.friction = 2;
        wheelFixtureDef.restitution = .7f;

        focus = new Focus(world, fixtureDef, wheelFixtureDef, 50, 14);

        wheelFixtureDef.shape.dispose();
        fixtureDef.shape.dispose();


        Gdx.input.setInputProcessor(new InputMultiplexer(new InputController() {
            @Override
            public boolean keyDown(int keycode) {
                switch(keycode) {
                    case Input.Keys.ESCAPE:
                        dispose();
                        break;
                    case Input.Keys.R:
                        camera.zoom = 1;
                        break;
                    case Input.Keys.PLUS:
                        camera.zoom = 10;
                        break;
                    case Input.Keys.MINUS:
                        camera.zoom = 1;
                        break;
                }
                return false;
            }



            @Override
            public boolean scrolled(int amount) {
                if(amount == -1 && camera.zoom <= MIN_ZOOM) {
                    camera.zoom = MIN_ZOOM;
                } else {
                    camera.zoom += amount / PIXELS_PER_METER;
                }
                return false;
            }
        },focus));
    }

    @Override
    public void render(float delta) {
        Gdx.gl.glClearColor(0, 0, 0, 1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

        world.step(TIME_STEP, VELOCITY_ITERATIONS, POSITION_ITERATIONS);
        camera.position.set(focus.getChassis().getWorldCenter().x,focus.getChassis().getWorldCenter().y,0);

        camera.update();

        String x;
        WheelJoint wj = (WheelJoint) focus.getChassis().getJointList().get(0).joint;
        x = (int)Math.abs(wj.getJointSpeed())+"";

        batch.begin();
        font.draw(batch, x, 20, 20);

        focus.getSpriteChassis().setPosition((Gdx.graphics.getWidth() / 2 - focus.getSpriteChassis().getWidth() / 2) + focus.getOffSetX(), (Gdx.graphics.getHeight() / 2 - focus.getSpriteChassis().getHeight() / 2) + focus.getOffSetY());


        focus.getSpriteChassis().setRotation(focus.getChassis().getAngle() * MathUtils.radiansToDegrees);
        focus.getSpriteChassis().setScale(1/camera.zoom);
        focus.getSpriteChassis().draw(batch);

        focus.getSpriteRearWheel().setPosition((Gdx.graphics.getWidth() / 2 - focus.getSpriteChassis().getWidth() / 2) , (Gdx.graphics.getHeight() / 2 - focus.getSpriteChassis().getHeight() / 2) );
        focus.getSpriteFrontWheel().setPosition((Gdx.graphics.getWidth() / 2 - focus.getSpriteChassis().getWidth() / 2) , (Gdx.graphics.getHeight() / 2 - focus.getSpriteChassis().getHeight() / 2) );
        //focus.getSpriteRearWheel().setPosition((Gdx.graphics.getWidth() / 2 - focus.getSpriteChassis().getWidth() / 2) + focus.getRwOffSet()*PIXELS_PER_METER*(1/camera.zoom), (Gdx.graphics.getHeight() / 2 - focus.getSpriteChassis().getHeight() / 2) + focus.getRwOffSetY()*PIXELS_PER_METER*(1/camera.zoom) );
        //focus.getSpriteFrontWheel().setPosition((Gdx.graphics.getWidth() / 2 - focus.getSpriteChassis().getWidth() / 2)+ focus.getFwOffSet()*PIXELS_PER_METER*(1/camera.zoom) , (Gdx.graphics.getHeight() / 2 - focus.getSpriteChassis().getHeight() / 2) + focus.getFwOffSetY()*PIXELS_PER_METER*(1/camera.zoom));

        focus.getSpriteRearWheel().setRotation(focus.getRearWheel().getAngle() * MathUtils.radiansToDegrees);
        focus.getSpriteFrontWheel().setRotation(focus.getFrontWheel().getAngle() * MathUtils.radiansToDegrees);
        focus.getSpriteRearWheel().setScale(1 / camera.zoom);
        focus.getSpriteRearWheel().draw(batch);
        focus.getSpriteFrontWheel().setScale(1 / camera.zoom);
        focus.getSpriteFrontWheel().draw(batch);

        batch.end();

        debugRenderer.render(world,  camera.combined);

    }

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

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

    @Override
    public void pause() { }

    @Override
    public void resume() { }

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

Can anyone help me understand? many thanks !!!

Answer 1

Box2D has a speed limit, which is about 2.0 units/timestep.
So if you step 60 times / second, you can move 2 * 60 = 120 units/second.
To increase the maximum speed you can decrease the timestep ie increase the number of steps/second.
If you, for example, increase it to 30, you can move up to 2 * 120 = 240 units/second.

Also make sure, that you are using meters as your unit. Box2D has been created with kg, meters and seconds in mind, so you should also use those units.