Ahhhh failed to create the electrons flow in light bulb. Planed to

1. add some particles around strings
2. restrain patterns to  fit within the lightbulb, using different canvas

Things worth mentioned:

• I  used keyPressed() to change the gravity. Kill the original gravity and use “A, W, D, S” keys to control the direction of force.

ParticleBehavior2D b = physics.behaviors.get(physics.behaviors.size()-1);
physics.removeBehavior(b);
if (key == 'a') {
physics.addBehavior(new GravityBehavior(new Vec2D(random(-0.3), random(-0.05, 0.05))));
}
else if (key == 'w') {
physics.addBehavior(new GravityBehavior(new Vec2D(random(-0.05, 0.05), random(-0.3))));
}
else if (key == 'd') {
physics.addBehavior(new GravityBehavior(new Vec2D(random(0.3), random(-0.05, 0.05))));
}
else if (key == 's') {
physics.addBehavior(new GravityBehavior(new Vec2D(random(-0.05, 0.05), random(0.3))));
}

•  Use the color function of Toxiclibs, measure the direction of the spring and then map it into 0~1, and then some crazy codes to set up the color of stroke.

for (VerletSpring2D s: strings) {
  float currHue = map(s.b.sub(s.a).heading(), -PI, PI, 0, 1);
  stroke(TColor.newHSV(currHue, 1, 1).toARGB());
  line(s.a.x, s.a.y, s.b.x, s.b.y);
}

Original version, without vertex to fill the mesh. Looks like seaweeds.

Looks like worms.

And here are some tutorials and examples I found useful!

1. Nature of Code by Daniel Shiffman
2. SpringPlay by Justin Pinkney
3. @ creativeapplications