Scripts on nodes

A script is a pub class named after its file, with door_bell.bs holding DoorBell. Each node the file is attached to gets one object of the class, and the object lives as long as the node does.

// scripts/spinner.bs
pub class Spinner {
    pub speed: float = 2.0,
    pub clockwise: bool = true,
    node: Node,
    angle: float,
    direction: float,
}

impl Spinner {
    fn init() {
        self.angle = 0.0;
        self.direction = if self.clockwise { 1.0 } else { -1.0 };
    }

    fn update(dt: float) {
        if input::action_just_pressed("reverse") {
            self.direction = -self.direction;
        }
        self.angle += dt * self.speed * self.direction;
        self.node.transform.rotation_euler = vec3(0.0, self.angle, 0.0);
    }
}

[[nodes]]
name = "Spinner"
script = { source = "scripts/spinner.bs" }

• A field named node of type Node is set to the node the object sits on.
• A field with no default starts empty: 0, 0.0, false, "", an empty list or map, nil, or no node.
• The engine makes the object, so a script never writes its class as a literal.

Hooks

The engine calls these methods when the class declares them.

Simulation belongs in fixed_update, which is what keeps a replay identical. Drawing and input feel belong in update. See Determinism.

A scene inits children before parents.

Methods the engine calls by name

Any other method is yours. The engine also calls one by name when something names it: a widget's on_click = "pressed" in a scene, or on_hit for an event.

// scripts/menu.bs
pub class Menu {
    node: Node,
    presses: int,
}

impl Menu {
    pub fn pressed() {
        self.presses += 1;
        log::info("pressed {self.presses} times");
    }
}

Reloading

Saving a script recompiles it, and each object carries over every field that kept its name and type. A field the new code adds starts at its default, and a field it dropped goes. A running task does not carry over.