Calling functions

In general, the gdext library maps Godot functions in a way that feels as idiomatic as possible in Rust. Sometimes, signatures differ from GDScript, and this page will go into such differences.

Godot classes
Godot functions
Singletons
Default parameters
Dynamic calls

Godot classes

Godot classes are located in the godot::engine module. Some often-used ones like Node, RefCounted, Node3D etc. are additionally re-exported in godot::prelude.

The majority of Godot's functionality is exposed via functions inside classes. Please don't hesitate to check out the API docs.

Godot functions

For methods, the first parameter is the receiver, i.e. the object on which the method is called.

The Rust API infers the mutability information from the GDExtension API and uses either &self or &mut self accordingly. Note that this is informational only and bears no safety implications, but it can help you make code more expressive.

#![allow(unused)]
fn main() {
// Call with &self receiver.
let node = Node::new_alloc();
let path = node.get_path();

// Call with &mut self receiver.
let mut node = Node::new_alloc();
let other: Gd<Node> = ...;
node.add_child(other);
}

Associated functions (called "static" in GDScript) are invoked on the type itself.

#![allow(unused)]
fn main() {
Node::print_orphan_nodes();
}

Singletons

Singleton classes (not to be confused with autoloads, which are sometimes called singletons, too) provide a singleton() function to access the one true instance. Methods are then invoked on that instance:

#![allow(unused)]
fn main() {
let input = Input::singleton();
let jump = input.is_action_pressed("jump");
let mouse_pos = input.get_mouse_position();

// Mutable actions need mut:
let mut input = input;
input.set_mouse_mode(MouseMode::CAPTURED);
}

There are discussions about providing methods directly on the singleton type instead of requiring the singleton() call. This would however lose the mutability information, among a few other things.

Default parameters

GDScript supports default values for parameters. If no argument is passed, then the default value is used. As an example, we can use AcceptDialog.add_button(). The GDScript signature is:

Button add_button(String text, bool right=false, String action="")

So you can call it in the following ways from GDScript:

var dialog = AcceptDialog.new()
var button0 = dialog.add_button("Yes")
var button1 = dialog.add_button("Yes", true)
var button2 = dialog.add_button("Yes", true, "confirm")

In Rust, we still have a base method AcceptDialog::add_button(), which takes no default arguments. It can be called in the usual way:

#![allow(unused)]
fn main() {
let dialog = AcceptDialog::new_alloc();
let button = dialog.add_button("Yes".into());
}

Because Rust does not support default parameters, we have to emulate the other calls differently. We decided to use the builder pattern.

Builder methods in gdext receive the _ex suffix. Such a method takes all required parameters, like the base method. It returns a builder object, which offers methods to set the optional parameters by their name. Eventually, a done() method concludes the builder and returns the result of the Godot function call.

For our example, we have the AcceptDialog::add_button_ex() method. These two calls are exactly equivalent:

#![allow(unused)]
fn main() {
let button = dialog.add_button("Yes".into());
let button = dialog.add_button_ex("Yes".into()).done();
}

You can additionally pass optional arguments using methods on the builder object. Just specify the arguments you need. The nice thing here is that you can use any order, and skip any parameters -- unlike GDScript, where you can only skip ones at the end.

#![allow(unused)]
fn main() {
// Equivalent in GDScript: dialog.add_button("Yes", true, "")
let button = dialog.add_button_ex("Yes".into())
    .right(true)
    .done();

// GDScript: dialog.add_button("Yes", false, "confirm")
let button = dialog.add_button_ex("Yes".into())
    .action("confirm".into())
    .done();

// GDScript: dialog.add_button("Yes", true, "confirm")
let button = dialog.add_button_ex("Yes".into())
    .right(true)
    .action("confirm".into())
    .done();
}

Dynamic calls

Sometimes, you want to invoke functions that are not exposed in the Rust API. These could be functions you wrote inside custom GDScript code, or methods from other GDExtensions.

When you don't have the static information available, you can use Godot's reflection APIs. Godot provides Object.call() among others, which is exposed in two ways in Rust.

If you expect a call to succeed (since you know the GDScript code you wrote), use Object::call(). This method will panic if the call fails, providing a detailed message.

#![allow(unused)]
fn main() {
let node = get_node_as::<Node2D>("path/to/MyScript");

// Declare arguments as a slice of variants.
let args = &["string".to_variant(), 42.to_variant()];

// Call the method dynamically.
let val: Variant = node.call("my_method", args);

// Convert to a known type (may panic; try_to() doensn't).
let vec2 = val.to::<Vector2>();
}

If instead you want to handle the failure case, use Object::try_call(). This method returns a Result with the result or a CallError error.

#![allow(unused)]
fn main() {
let result: Result<Variant, CallError> = node.try_call("my_method", args);

match result {
    Ok(val) => {
        let vec2 = val.to::<Vector2>();
        // ...
    }
    Err(err) => {
        godot_print!("Error calling method: {}", err);
    }
}
}

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