How to make a realistic roulette ball spinning animation

Question

I'm using PhysicsJS to make a 2D roulette ball spinning animation.

So far, I've implemented the following:

• used a constraint so that the ball wouldn't "fly away":
  rigidConstraints.distanceConstraint( wheel, ball, 1 );
• used drag to slow down the ball:
  world.add(Physics.integrator('verlet', { drag: 0.9 }));
• made the wheel attract the ball, so that it would fall towards it when the drag has slowed down the ball enough

My questions:

1. how do I gradually slow down the ball spinning?
   I have already a very high drag value, but it doesn't look like it's doing anything
2. how do I make attraction towards the wheel work?
   The distance constraint should keep the ball from escaping, not from getting closer to the wheel.
3. why does angularVelocity: -0.005 not work at all on the wheel?

My code, also on JSfiddle

Physics(function (world) {
    var viewWidth = window.innerWidth
        ,viewHeight = window.innerHeight
        ,renderer
        ;

    world.add(Physics.integrator('verlet', {
        drag: 0.9
    }));

    var rigidConstraints = Physics.behavior('verlet-constraints', {
        iterations: 10
    });

    // create a renderer
    renderer = Physics.renderer('canvas', {
        el: 'viewport'
        ,width: viewWidth
        ,height: viewHeight
    });

    // add the renderer
    world.add(renderer);
    // render on each step
    world.on('step', function () {
        world.render();
    });

    // create some bodies
    var ball = Physics.body('circle', {
        x: viewWidth / 2
        ,y: viewHeight / 2 - 300
        ,vx: -0.05
        ,mass: 0.1
        ,radius: 10
        ,cof: 0.99
        ,styles: {
            fillStyle: '#cb4b16'
            ,angleIndicator: '#72240d'
        }
    })

    var wheel = Physics.body('circle', {
        x: viewWidth / 2
        ,y: viewHeight / 2
        ,angularVelocity: -0.005
        ,radius: 100
        ,mass: 100
        ,restitution: 0.35
        // ,cof: 0.99
        ,styles: {
            fillStyle: '#6c71c4'
            ,angleIndicator: '#3b3e6b'
        }
        ,treatment: "static"
    });

    world.add(ball);
    world.add(wheel);

    rigidConstraints.distanceConstraint( wheel, ball, 1 );

    world.add( rigidConstraints );

    // add things to the world
    world.add([
        Physics.behavior('interactive', { el: renderer.el })
        ,Physics.behavior('newtonian', { strength: 5 })
        ,Physics.behavior('body-impulse-response')
        ,Physics.behavior('body-collision-detection')
        ,Physics.behavior('sweep-prune')
    ]);

    // subscribe to ticker to advance the simulation
    Physics.util.ticker.on(function( time ) {
        world.step( time );
    });

    // start the ticker
    Physics.util.ticker.start();
});

Answer 1

1. Drag has a bug in that version of PhysicsJS, try using the most updated version from github. https://github.com/wellcaffeinated/PhysicsJS/issues/94

2. Unfortunately the distance constraint imposes a fixed distance. So to prevent the ball's escape in that way, you'd need to implement your own behavior. (more below)

3. You'll have to change behavior: "static" to be behavior: "kinematic". Static bodies don't ever move on their own.

To create a custom behavior check out the documentation here: https://github.com/wellcaffeinated/PhysicsJS/wiki/Behaviors#creating-a-custom-behavior

In order to get the functionality you're describing, you'll need to do something like this:

// in the behave method
// calculate the displacement of the ball from the wheel... something like....
disp.clone( wheel.state.pos ).vsub( ball.state.pos );
// if it's greater than max distance, then move it back inside the max radius
if ( disp.norm() > maxDist ){
    var moveBy = disp.norm() - maxDist;
    disp.normalize(); // unit vector towards the wheel
    disp.mult( moveBy );
    ball.state.pos.vadd( disp ); // move it back inside the max radius
}

Of course, this is a "just get it done" way of doing this but it should work.