box2d kinematic body wont move

Question

As far as I understand it, this should cause the body to move. I have an update method in the class but I'm not sure what else to add. I am using box2d as part of libgdx. Everywhere I've looked it just says to set the linear velocity, but it isn't working.

    BodyDef bodyDef = new BodyDef();
    bodyDef.position.set(new Vector2(pos.x, pos.y));
    bodyDef.type = BodyDef.BodyType.KinematicBody;
    bodyDef.linearDamping = 0.0f;
    bodyDef.angularDamping = 0.0f;
    unitBoxBody = world.createBody(bodyDef);

    PolygonShape player = new PolygonShape();
    player.setAsBox(unit * xSize, unit * ySize); 
    FixtureDef fixtureDef = new FixtureDef();
    fixtureDef.shape = player;

    fixtureDef.density = 0.0f;
    fixtureDef.friction = 0.0f; 
    fixtureDef.restitution = 0.0f;
    fixture = unitBoxBody.createFixture(fixtureDef);
    player.dispose();
    unitBoxBody.setLinearVelocity(10, 0);

I have used numerous large and small values for the velocity with no change.

Why fixtureDef.density = 0.0f, this seems kind of odd since if you apply force to a massless object, it would have infinite acceleration. Not too sure how that's handled by Box2D. Also are you calling world.step() in your main loop? — XiaoChuan Yu
Add the render(float delta) method or your principal loop method — Alex Sifuentes
@XiaoChuanYu code's just copied from another object I'm using where that doesn't really matter. I'll change it and see if it helps. Yes I am calling step. I have no problems with literally every other object in the program. Edit: changing density does nothing. — Dreamtime
@AlexandroSifuentesDíaz this isn't the issue. Every thing else works fine and I can control other types of bodies with no issues. — Dreamtime
Have you tried copying only the above code into another blank project and see if the body moves? — XiaoChuan Yu

jobr97 jobr97 · Accepted Answer · 2015-08-21T06:46:52

You have to make your world step:

Put this in your render() method: world.step(TIMESTEP, VELOCITY_ITERATIONS, POSITION_ITERATIONS);

and define These variables:

private static final float TIMESTEP = 1.0f / 60.0f; 
private static final int VELOCITY_ITERATIONS = 8; 
private static final int POSITION_ITERATIONS = 3;

box2d kinematic body wont move

1 Answers