gdrust

A library for making gdnative-rust a bit more GdScript-like. This contains two main parts:

1. A #[gdrust] macro for simplifying some rust code and making it more GdScript-like.
2. A set of "unsafe" functions to make things more concise at the risk of crashing.

Goals

Ultimately, the goal of this project is rust development for Godot more concise in 90% of cases. There may be some edge cases only "true" rust can resolve, and this project should not comprimise its simplicity for the sake of covering every case.

Current State

Right now, this project is in an early alpha state. The documented parts should work as expected, but the api is likely to change.

Getting Started

gdrust surfs on gdnative-rust, so you must have gdnative-rust setup before you start looking at gdrust. Follow their Getting Started Guide.

Once gdnative-rust is installed, you can install gdrust by adding it as a dependency. Unfortunately, due to the way gdnative-rust macros work, you must have both gdnative-rust and gdrust added as dependencies side-by-side, and you must choose compatible versions. See the "Compatibilty" section below.

[dependencies]
gdnative = "0.9.3"
gdrust = { git = "https://github.com/wyattjsmith1/gdrust.git" }

Once installed, simply use the gdrust macro:

use gdrust::macros::gdrust;
use gdnative::api::Node;

#[gdrust(extends = Node)]
struct HelloWorld {
    #[export]
    #[default(10)]
    test: u64,
}

That's it!

Read more below for details and gotchas with exporting properties and signals, as well as an in-depth comprehensive example.

#[gdrust] Macro

Exporting classes

Anything in a #[gdrust] macro is avaliable for export.

#[gdrust(extends = Node)]
pub struct ClassName {
   // Same as `class_name ClassName extends Node` in GdScript.
}

The extends = {classname} is optional, and may be omitted if you are just extending Object:

#[gdrust::macros::gdrust]
struct ClassName {
    // Same as `class_name ClassName extends Object` in GdScript.
}

You can still have custom derives and attributes on your class. Any attributes on the struct will be added:

#[gdrust::macros::gdrust]
#[derive(Debug)]
struct ClassName {
    // `ClassName` will derive `Debug`
}

After you create the class and export properties and signals, create your impl block as usual. Note, you should not create the new function. That is provided by the macro:

#[gdnative::methods]
impl ClassName {
    #[export]
    fn _ready(&self, _owner: TRef<KinematicBody>) {
        gdnative::godot_print!("Hello World!")
    }
}

Exporting Properties

The syntax for exporting properties is intended to mirror GdScript as closely as possible. Due to the upcoming 4.0 release, gdrust uses the 4.0 exports. You can read all about the different types of exports there.

In general, use attribute syntax (#[export_...]), and remove the @ at the start of GdScript export. For example:

@export_range(1, 10, 2, "or_greater") var my_range: int

Becomes:

#[export_range(1, 10, 2, "or_greater")]
my_range: i32 // or i64 if you want

Everything should be implemented as defined in Godot's docs except for the following:

1. #[no_export] can be used to not export a variable. This should be used for all Rust-native types (doesn't implement Export) or if you want the variable to be "private".
2. The 4.0 docs define @export_node_path(Type1, Type2) as a way to export a NodePath which only matches nodes with given types. This is partially implemented, but won't be finished until 4.0 because there is currently not export hint for NodePaths. You can currently include this export in your code, but it will allow a NodePath to any type.
3. Nullability is handled with an Option.
4. Every exported property will require both a type and a default value. If no default value is provided, Default::default() will be used. If you are referencing a Godot object and not a "primitive", this must be wrapped in a Ref.
5. Currently, arrays are not supported. This is simply because I am not confident the syntax has been finalized. On Godot's site, it shows the traditional export(Array, int) var ints = [1, 2, 3]. I am guessing they will switch to some sort of @export_array style. Once that is finalized, adding it should be easy.

Default

You may set a custom default value using the #[default(value)] annotation. If it is not defined, Default::default() is used.

Exporting Signals

The syntax for exporting signals is also intended to mirror GdScript as closely as possible. The syntax is:

#[gdrust]
#[signal(signal_name(arg_name: I64, arg2_name: F64 = 10.0))]
#[signal(other_signal(arg_name: Bool = true, arg2_name: GodotString = "default"))]
struct Class;

Similar to properties, there are a few gotchas with signals:

1. Like properties, every signal must have a type. Unlike properties, the type must be one of:

• A VariantType
• A Godot object without a Ref (like a KinematicBody).

I know this is a little weird, and I'd like to smooth it out a bit. Suggestions are welcome.

2. Unlike GdScript, gdrust signal arguments may have optional default values.

When a signal is exported, there will be a const with its name. Look at the simple_signal signal in the example below to see how it can be used.

Comprehensive Example

This example should contain all possibilities for exporting properties and signals. It is used for testing as well.

use gdnative::api::{KinematicBody, Node, RigidBody, Texture};
use gdnative::prelude::{Color, InitHandle, NodePath, ToVariant};
use gdnative::{godot_init, Ref, TRef};
use gdrust::macros::gdrust;

#[gdrust(extends = Node)]
#[signal(my_signal(arg1: F64, arg2: GodotString = "test".to_string()))]
#[signal(simple_signal(arg:I64))]
#[derive(Debug)]
struct HelloWorld {
    #[export]
    #[default(10)]
    test_a: u8,

    #[no_export]
    test_failure: u8,

    #[default(10.0)]
    test_c: f32,

    #[export_range(0.0, 10.0)]
    simple_range: f32,

    #[export_range(0, 10, 2)]
    #[default(2)]
    step_range: u8,

    #[export_range(0, 10, "or_lesser")]
    #[default(10)]
    simple_range_or_lesser: u64,

    #[export_range(0.0, 10.0, 1.5, "or_lesser")]
    #[default(10.0)]
    simple_range_step_or_lesser: f64,

    #[export_range(0, 10, "or_greater")]
    #[default(10)]
    simple_range_or_greater: u64,

    #[export_range(0, 10, 10, "or_greater")]
    #[default(10)]
    simple_range_step_or_greater: u64,

    #[export_range(0, 10, 10, "or_lesser", "or_greater")]
    #[default(10)]
    range_with_all: u64,

    #[export]
    texture: Option<Ref<Texture>>,

    #[export_enum("This", "is", "a", "test")]
    #[default("This".to_string())]
    string_enum: String,

    #[export_enum("This", "will", "be", "enum", "ordinals")]
    int_enum: u32,

    #[export_file]
    file: String,

    #[export_file("*.png")]
    png_file: String,

    #[export_dir]
    dir: String,

    #[export_global_file("*.png")]
    glob_file: String,

    #[export_global_dir]
    glob_dir: String,

    #[export_multiline]
    #[default("This\nis\nmultiline\ntext".to_string())]
    multiline: String,

    #[export_exp_range(0.0, 10.0)]
    simple_exp_range: f32,

    #[export_exp_range(0, 10, 2)]
    #[default(2)]
    step_exp_range: u8,

    #[export_exp_range(0, 10, "or_lesser")]
    #[default(10)]
    simple_exp_range_or_lesser: u64,

    #[export_exp_range(0.0, 10.0, 1.5, "or_lesser")]
    #[default(10.0)]
    simple_exp_range_step_or_lesser: f64,

    #[export_exp_range(0, 10, "or_greater")]
    #[default(10)]
    simple_exp_range_or_greater: u64,

    #[export_exp_range(0, 10, 10, "or_greater")]
    #[default(10)]
    simple_exp_range_step_or_greater: u64,

    #[export_exp_range(0, 10, 10, "or_lesser", "or_greater")]
    #[default(10)]
    exp_range_with_all: u64,

    #[export]
    #[default(Color::rgba(0.0, 0.0, 0.0, 0.5))]
    color: Color,

    #[export_color_no_alpha]
    #[default(Color::rgb(0.0, 0.0, 0.0))]
    color_no_alpha: Color,

    #[export_flags("Fire", "Water", "Earth", "Wind")]
    spell_elements: u32,

    // TODO: NodePath types are only supported in 4.0
    #[export_node_path(KinematicBody, RigidBody)]
    physics_body: NodePath,

    #[export_flags_2d_physics]
    layers_2d_physics: u32,

    #[export_flags_2d_render]
    layers_2d_render: u32,

    #[export_flags_3d_physics]
    layers_3d_physics: u32,

    #[export_flags_3d_render]
    layers_3d_render: u32,
}

#[gdnative::methods]
impl HelloWorld {
    #[export]
    fn _ready(&self, owner: TRef<Node>) {
        gdnative::godot_print!("Hello World!");
        gdnative::godot_dbg!(self);
        owner
           .upcast::<Node>()
           .emit_signal(Self::SIMPLE_SIGNAL, &[0.to_variant()]);
    }
}

Pros and Cons

Like any piece of software, this is not without it's issues. This list is intended to accurately document the pros and cons to help people decide if this is the right project for them.

Pros

1. Simplifies the ClassBuilder chain and makes the code look more GdScripty
2. Generates a new
3. Synchronizes the property default with the new default. No more changing the default property value and not having it reflected in code.

Cons

1. Like many macros, when the input is correct, they work great. When the input is invalid, they give obscure error messages. I am trying to cover most of the common error cases with clear messages. If you see weird message, open an issue and I will help you out. In general, #[export*s should always use the same type of literals (all ints or all floats).

Unsafe Functions

One of the great things about rust is that it forces you to handle every possible case to ensure the runtime goes smoothly. One issue with this is game development is full of "well, I hope this works" cases in which error handling is ignored until runtime.

For example, let's say you want to get a child node and call set_emitting() on it. In gdnative-rust, you would do this:

unsafe {
    owner.get_node("Particles")
        .unwrap()
        .assume_safe()
        .cast::<Particles>()
        .unwrap()
        .set_emitting(true);
}

Compare to GdStript (without the $ sugar):

get_node("Particles").start_emitting()

Yes, the static typing does cause some verbosity in the rust example, but this is still a lot. gdrust exposes a cleaner method:

owner.expect_node::<Particles, _>("Particles").set_emitting(true)

Not quite as concise as GdScript, but still more concise than gdnative-rust. One thing to note: this function almost literally translates to the code above. There is an explicit unsafe block, and a variety of unwraps. This is very unsafe, but when will this fail? Only if you request an invalid node, or break the memory model. Rust is designed to make you recover, but how do you recover from a missing node at runtime? You will probably just unwrap anyways to appease the compiler.

As a result, this is called unsafe_functions because it is unsafe in the eyes of rust, but when compared to GdScript, this is pretty normal and safe.

You should definitely read about the panics each method can produce and understand gdnative-rust's memory model. Once you do, you should have the right judgement on when to use these helper functions.

Compatibility

Unfortunately, gdrust requires the gdnative dependency, and it can not be pub used due to the way gdnative's macros work. As as result, you must ensure you have a compatible version of both gdrust and gdnative. This table will be updated with all compatible versions:

gdrust	gdnative-rust
0.1.0	0.9.+

Additional Reading

• Contributing
• Reasoning for this project
• FAQs

License: MIT