I have created a basic example of a falling ball but I am slightly confused to why the object is not accelerating while falling. It is travelling at constant speed which isn't what I would expect. This is my first day using Box2D I assume I have missed something basic, but can't figure it out.
public PhysicsWorld() {
// Step 1: Create Physics World Boundaries
Vec2 gravity = new Vec2(0, 20);
boolean doSleep = true;
world = new World(gravity, doSleep);
// Dynamic Body
BodyDef bodyDef = new BodyDef();
bodyDef.type = BodyType.DYNAMIC;
bodyDef.position.set(100, 100);
body = world.createBody(bodyDef);
MassData md = new MassData();
md.mass = 5;
body.setMassData(md);
PolygonShape dynamicBox = new PolygonShape();
dynamicBox.setAsBox(1, 1);
FixtureDef fixtureDef = new FixtureDef();
fixtureDef.shape = dynamicBox;
fixtureDef.density = 1;
fixtureDef.friction = 0.3f;
body.createFixture(fixtureDef);
velocityIterations = 6;
positionIterations = 2;
}
public void update() {
world.step(timeStep, velocityIterations, positionIterations);
Log.i("body", "x: " + body.getPosition().x + " y: " + body.getPosition().y);
}
Output:
01-22 21:17:20.750: I/body(7698): x: 100.0 y: 102.0
01-22 21:17:20.777: I/body(7698): x: 100.0 y: 104.0
01-22 21:17:20.796: I/body(7698): x: 100.0 y: 106.0
01-22 21:17:20.824: I/body(7698): x: 100.0 y: 108.0
01-22 21:17:20.847: I/body(7698): x: 100.0 y: 110.0
I would expect gravity to be applied each iteration and increase the balls speed in Y.
This is because the velocity is capped by the engine and you are not using proper world coordinates. Think of it as a meter-kilogram-second system. You have a 1 by 1 meter box falling at 2 meters per 1/40th of a second, or 80 meters per second. That's pretty fast.