Doors, lifts and buttons

since 0.4.0 or earlier Simulation, audio and XR

Open the live demo · Read the source · View on GitHub

A door, a lift and a moving platform are one machine — a kinematic body sliding along an offset at a fixed speed — with three different rules for when to move. A button is a separate thing entirely: it does nothing itself, it only relays an activation to whatever it is wired to, by name.

Step 1: A world for mechanisms to live in #

MechanismWorld holds every mechanism in the level and the collision world they move through.

final world = CollisionWorld();
final mechanisms = MechanismWorld(world);

Step 2: Wire a button to a door #

Door owns a collider and a travel offset. Button owns a collider of its own and a target: the name of whatever it should switch on.

final doorCollider = world.addBox(Vector3(5, 1, 0), Vector3(1, 2, 0.2));
final door = mechanisms.add(
  Door(
    name: 'north-door',
    collider: doorCollider,
    travel: Vector3(0, 2, 0),
  ),
);
final buttonCollider = world.addBox(
  Vector3(0, 1, 0),
  Vector3(0.3, 0.3, 0.3),
);
mechanisms.add(
  Button(
    name: 'door-button',
    target: 'north-door',
    collider: buttonCollider,
  ),
);

Step 3: Press it and watch the door open #

activate finds the mechanism by name and calls its activate. A button relays that to its target; a door starts moving towards open.

mechanisms.activate('door-button', const Activation());
for (var i = 0; i < 180; i++) {
  mechanisms.step(1 / 60);
}

The door starts closed, at progress 0. After the button is pressed and the world is stepped forward, the door reaches progress 1 and reports itself open, well inside the three seconds it is given to hold there.

Step 4: Press it and watch #

The door on this page is the one wired above, drawn: its collider is what the mechanism moves, and the picture follows the collider. Press the button, or let it press itself, and the door slides up out of its frame, waits, and comes back down; the bar on the right is its progress, and the button lights while the activation is on its way.

// The same door and button, running: the door's collider is what the
// mechanism moves, and the picture follows it.
final CollisionWorld world = CollisionWorld();
_mechanisms = MechanismWorld(world);
_doorCollider = world.addBox(Vector3(5, 1, 0), Vector3(1, 2, 0.2));
_door = _mechanisms.add(
  Door(
    name: 'north-door',
    collider: _doorCollider,
    travel: Vector3(0, 2, 0),
  ),
);
_mechanisms.add(
  Button(
    name: 'door-button',
    target: 'north-door',
    collider: world.addBox(Vector3(0, 1, 0), Vector3(0.3, 0.3, 0.3)),
  ),
);

_mechanisms.activate('door-button', const Activation());