Components

Creating a Bevy component

Let’s start with a normal Bevy component.

use bevy::prelude::*;
use godot::prelude::*;

#[derive(Component)]
struct Health {
	flags: u32,
	position: Vector2,
	current_hp: u32,
	maximum_hp: u32,
}

This is a completely valid and usable component in Bevy💋Godot! Add it to any entity as you like!

Creating a Kissing component

In Bevy💋Godot, a “kissing” component is a component that is exposed and visible in the Godot editor (it crosses the boundary and kisses Godot).

To make a “kissing” component, just add the KissingComponent derive.

use bevy::prelude::*;
use godot::prelude::*;
use bevy_kissing_godot::prelude::*;

#[derive(Component, KissingComponent)]
struct Health {
	flags: u32,
	position: Vector2,
	current_hp: u32,
	maximum_hp: u32,
}

This will appear in the list of components in the Godot editor, but it won’t have any fields to edit!!

Creating a configurable Kissing component

To allow the fields of your kissing component to be editable in Godot, you use the #[export] attribute. This attribute works exactly as it does in gdext (the attribute is passed verbatim to gdext). This means you can use all the gdext parameters for this attribute as well!

use bevy::prelude::*;
use godot::prelude::*;
use bevy_kissing_godot::prelude::*;

#[derive(Component, KissingComponent)]
struct Health {
	#[export(enum = (Segmented = 1, Round = 2, Stacked = 3))] // added
	flags: u32,

	#[export] // added
	position: Vector2,

	#[export(range = (0, 1000))] // added
	maximum_hp: u32,

	current_hp: u32,
}

Setting initial value

To set the initial (and default) value for a property on a kissing component, the #[initial_value] attribute can be used. The expression is passed to an #[init(val = X)] attribute on the component’s editor object.

For literals, the #[initial_value = VALUE] syntax can be used. Rust does not allow all expressions for that attribute syntax, so for more complicated expressions, #[initial_value(VALUE)] must be used.

use bevy::prelude::*;
use godot::prelude::*;
use bevy_kissing_godot::prelude::*;

#[derive(Component, KissingComponent)]
struct Health {
	#[export(enum = (Segmented = 1, Round = 2, Stacked = 3))]
	#[initial_value = 2] // added
	flags: u32,

	#[export]
	#[initial_value(Vector2::new(100., 100.))] // added
	position: Vector2,

	#[export(range = (0, 1000))]
	#[initial_value = 10] // added
	maximum_hp: u32,

	current_hp: u32,
}

Post-constructor

The kissing component is constructed directly from the values provided by the editor. However, you can run a function to modify the component immediately after it’s constructed. Simply assign a function identifier to on_construct as an argument to #[kissing_component].

use bevy::prelude::*;
use godot::prelude::*;
use bevy_kissing_godot::prelude::*;

#[derive(Component, KissingComponent)]
#[kissing_component(on_construct = health_on_construct)] // added
struct Health {
	#[export(enum = (Segmented = 1, Round = 2, Stacked = 3))]
	#[initial_value = 2]
	flags: u32,

	#[export]
	#[initial_value(Vector2::new(100., 100.))]
	position: Vector2,

	#[export(range = (0, 1000))]
	#[initial_value = 10]
	maximum_hp: u32,

	current_hp: u32,
}

// The function just takes a mutable reference to the struct.
// Use Bevy's `on_add` if you want to make queries.
fn health_on_construct(component: &mut Health) {
	// We want the hp to start at the maximum value.
	component.current_hp = component.maximum_hp;
}