gd-props

Resources are akin to the versatile props that set the scene for an interactive masterpiece on the stage of game world. Much like actors skillfully employ props to enrich their storytelling, game objects leverage resources to craft a compelling virtual narrative. The mastery lies in the thoughtful selection and optimization of these digital tools, guaranteeing a captivating performance as players step into the spotlight of the gaming world.

Custom resources created with godot-rust can be very useful. However, as the game data becomes complex, the workflow available out of the box can be quite limiting. By default, Godot saves all resources into .tres and .res files, preserving only the state of fields marked with #[export]. This limitation confines the saving of state only to fields converted to Godot-compatible types.

gd-props aims to address this issue by providing an alternative strategy for loading and saving resources, relying fully on serde serialization and deserialization. Resources can be saved in two formats:

• .gdron: Based on the Ron format from the ron crate. Intended for human-readable output during development.
• .gdbin: Based on the MessagePack format from the rmp_serde crate. Intended for faster serialization and deserialization
• times, especially in exported games.

Limitations

Currently gd-props supports only Resources without the Base<Resource> field.

If you include gd-props in your dependencies, you need use utilize godot crate with the feature experimental-threads enabled.

This necessity arises from Godot's utilization of registered ResourceFormatLoaders methods during InitLevel::Editor on an additional thread, which cannot be inhibited. The godot crate, by default, prohibits multi-threading (triggering a panic in debug builds), as it is still not deemed safe by the maintainers.

To monitor the current status of the experimental-threads feature requirement, you can follow this this issue.

Current Features

The following features are currently available. More will be listed in the In Development section.

• GdProp derive macro for custom Resources, making them savable to .gdron and .gdbin formats.
• serde_gd module containing submodules to be used with serde, making it easier to implement Serialize and Deserialize for your custom resources.
• gd_props_plugin macro, which handles:
  • setting up ResourceFormatSaver and ResourceFormatSaver to handle .gdron and .gdbin formats.
  • setting up EditorPlugin and EditorExportPlugin to handle export of .gdron and .gdbin formats.
  • during export, all .gdron files are transformed into .gdbin, as the later is more compact and much faster to load.

In Development

This crate is not production-ready ⚠️

This crate is early in development, and its API may change. Contributions, discussions, and informed opinions are very welcome.

GdProp macro

Consider a scenario where you have a resource with a structure similar to the one below. You might contemplate transforming a HashMap into Godot's Dictionary, but this conversion could entail sacrificing some of its advantages. On the other hand, for structs like StatModifiers that you don't intend to handle as a Resource, there is a risk of loss when saving the resource with Godot's ResourceSaver.

#[derive(GodotClass, Serialize, Deserialize, GdProp)]
#[class(base=Resource)]
pub struct Statistics {
  /// Current character level - only available fully on Godot editor side. Rest can be accessed by other Rust GodotClasses.
  #[var]
  pub level: u32,
  /// All stats
  pub stats: HashMap<GeneralStat, usize>,
  /// Experience currently gained by the character. Every 100 experience points grants a level up with the chance of increasing stats.
  pub exp: usize,
  /// Amount of bane needed to be applied to the character - the higher, the more *boons* it amassed.
  pub bane: usize,
  /// Modifiers from [StatModEffect]. Key is the number of turns left, while value is the stat modifiers.
  pub effect_mods: HashMap<usize, StatModifiers>,
  /// Modifiers from equipped items. Key is the index of the item.
  pub item_mods: HashMap<usize, StatModifiers>,
  /// Modifiers from character class
  pub class_mods: StatModifiers,
}

GdProp derive macro implements GdProp trait, and makes the Resource saveable with our gd-props straight to .gdron and .gdbin file.

The .gdron format is a slightly modified Ron file, distinguished by the inclusion of a header containing the struct identifier or resource class name. For a random object of the above structure, the resulting file might look like this:

(gd_class:"Statistics",uid:"uid://bwgy4ec84b8xv")
(
    level: 3,
    stats: {
        Mv: 0,
        Lck: 7,
        Def: 7,
        Mag: 7,
        Agi: 9,
        HP: 28,
        Res: 3,
        Dex: 7,
        Str: 7,
    },
    exp: 0,
    bane: 4,
    effect_mods: {},
    item_mods: {},
    class_mods: (
        x: {},
    ),
)

The header, in this case, contains Statistics, signifying the class name of the serialized struct. This format is designed for human-readable output during development, aiding in easy inspection and modification of the saved resources. Additionally, Godot's uid path is also preserved there.

On the other hand, the .gdbin format is based on the MessagePack format from the rmp_serde crate. It is intended for faster serialization and deserialization times, especially in exported games, and in other aspects is analogous to .gdron.

Both formats, whether human-readable or optimized for performance, offer the flexibility to choose the serialization strategy that best suits your development and deployment needs.

Both file are recognizable by Godot editor, can be loaded through it and attached to some Godot class.

Bundled resources

What if we have a Resource which contains another resource, which we would want to save as a bundled resource? There are two modules that handle this case:

• gd_props::serde_gd::gd_option - for Option<Gd<T>> fields,
• gd_props::serde_gd::gd - for Gd<T> fields,
• gd_props::serde_gd::gd_array - for Array<Gd<T>> fields,
• gd_props::serde_gd::gd_hashmap - for HashMap<K, Gd<T> fields.

There are some requirements for this to work:

• T needs to be User-defined GodotClass inheriting from Resource,
• T needs to derive Serialize and Deserialize.

Example

#[derive(GodotClass, Serialize, Deserialize, GdProp)]
#[class(base=Resource)]
pub struct CharacterData {
    #[export]
    affiliation: CharacterAffiliation,
    #[export]
    #[serde(with="gd_props::serde_gd::gd_option")]
    statistics: Option<Gd<Statistics>>,
}

Upon saving, we receive file as below:

(gd_class:"CharacterData",uid:"uid://dfa37uvpqlnhq")
(
    affiliation: Player,
    statistics: Some((
        level: 3,
        stats: {
            Def: 7,
            Dex: 7,
            Lck: 7,
            Mag: 7,
            Res: 3,
            Mv: 0,
            HP: 28,
            Agi: 9,
            Str: 7,
        },
        exp: 0,
        bane: 4,
        effect_mods: {},
        item_mods: {},
        class_mods: (
            x: {},
        ),
    )),
)

External Resources

If you desire to preserve a sub-resource as an External Resource, akin to regular resource saving in Godot, gd-props provides two additional modules:

• gd_props::serde_gd::ext_option - designed for Option<Gd<T>> fields,
• gd_props::serde_gd::ext - designed for Gd<T> fields,
• gd_props::serde_gd::ext_array - for Array<Gd<T>> fields,
• gd_props::serde_gd::ext_hashmap - for HashMap<K, Gd<T> fields.

To enable this functionality, a few requirements must be met:

• T needs to be a Resource.
• T must be a standalone Resource and be savable to and loadable from a file.

This approach offers several advantages:

• T doesn't necessarily need to be a User-defined GodotClass, making it compatible with built-in resources.
• External Resource instances are reused whenever they are referenced, enhancing efficiency and reducing redundancy in the game data.

Example

#[derive(GodotClass, Serialize, Deserialize, GdProp)]
#[class(base=Resource)]
pub struct CharacterData {
    #[export]
    affiliation: CharacterAffiliation,
    // As `statistics` is User-defined Resource, so we could also use `gd_option` module to bundle the Resource.
    #[export]
    #[serde(with="gd_props::serde_gd::ext_option")]
    statistics: Option<Gd<Statistics>>,
    #[export]
    #[serde(with="gd_props::serde_gd::ext_option")]
    nothing_is_here: Option<Gd<Resource>>,
    #[export]
    #[serde(with="gd_props::serde_gd::ext_option")]
    texture: Option<Gd<CompressedTexture2D>>,
}

Upon saving to .gdron format we receive file as below:

(gd_class:"CharacterData",uid:"uid://dfa37uvpqlnhq")
(
    affiliation: Player,
    statistics: ExtResource((
        gd_class: "Statistics",
        uid: "uid://dixv2uvh8waug",
        path: "res://statistics.gdron",
    )),
    nothing_is_here: None,
    texture: ExtResource((
        gd_class: "CompressedTexture2D",
        uid: "uid://ci3y6557pn0o",
        path: "res://icon.svg",
    )),
)

GdProp tooling

Now that we have Rust resources fully serializable to .gdron and .gdprop, the next step is to provide tools for saving and loading them within the Godot engine. The default ResourceSaver and ResourceLoader are unaware of our .gdron and .gdbin files.

Also, by default the files won't be included into exported game, and actually we want to have a say in how they should be exported.

To automatically define all tool GodotClass needed to handle introduced formats, the #[gd_props_plugin] macro should be used. Below example that creates all needed tools and register two GdProps-annotated resources to be recognized by them.

use godot::prelude::*;
use gd_props::gd_props_plugin;

// Macro creates four different GodotClasses and registers two resources implementing `GdProp`
#[gd_props_plugin]
#[register(CharacterData, Statistics)]
pub(crate) struct PropPlugin;

// Plugin and Exporter are only available in-editor for exporting resources.
assert_eq!(PropPlugin::INIT_LEVEL, InitLevel::Editor);
assert_eq!(PropPluginExporter::INIT_LEVEL, InitLevel::Editor);

// Loader and Saver are available in scenes for loading/saving registered resources.
assert_eq!(PropPluginSaver::INIT_LEVEL, InitLevel::Scene);
assert_eq!(PropPluginLoader::INIT_LEVEL, InitLevel::Scene);

Custom Format Saving and Loading with GdProp

After above, all that is left for Godot Editor to use our new ResourceFormatSaver and ResourceFormatLoader is to register them upon loading out gdextension to Godot's ResourceSaver and ResourceLoader, respectively. It can be achieved with provided associated methods in GdPropSaver and GdPropLoader traits.

// lib.rs
use godot_io::traits::{GdPropLoader, GdPropSaver};

struct MyExtension;

#[gdextension]
unsafe impl ExtensionLibrary for MyExtension {
    fn on_level_init(_level: InitLevel) {
        if _level == InitLevel::Scene {
            PropPluginLoader::register_loader();
            PropPluginSaver::register_saver();
        }
    }
    // And we need to unregister them when editor is closing!
    fn on_level_deinit(deinit: InitLevel) {
       if deinit == InitLevel::Scene {
           PropPluginLoader::unregister_loader();
           PropPluginSaver::unregister_saver();
       }
    }
}

Custom format export

Contrary to Loader and Saver, just a definition of EditorPlugin GodotClass is enough to handle the resources on export and no extra steps are needed. Besides adding the custom format resources into the exported executable, all resources in .gdron format will be translated into .gdbin, as main reason for the former (being human-readible) isn't needed anymore, and the later is more concise and faster to load.

As comparison from gd-rehearse run shows, the difference is meaningiful, so currently there is no way to opt-out of the conversion.

On debug (both Godot and Rust) build, where resources with paths ending with .gdron are saved/loaded as .gdron files.

--------------------------------------------------------------------------------
   Running Rust benchmarks
--------------------------------------------------------------------------------
                                              min       median
   gdbin.rs:
   -- serialize                  ...     27.260μs     29.396μs
   -- deserialize                ...     73.402μs     73.855μs
   -- gdbin_save                 ...    350.893μs    360.174μs
   -- gdbin_load                 ...    228.172μs    230.172μs

   gdron.rs:
   -- serialize                  ...     37.871μs     40.088μs
   -- deserialize                ...     82.897μs     83.356μs
   -- gdron_save                 ...    492.388μs    502.603μs
   -- gdron_load                 ...    979.330μs    988.216μs

On release (both Godot and Rust) build, where resources with paths ending with .gdron are remapped to .gdbin, the times are similiar for both formats: slightly higher times on gdron are probably caused by Godot's remap system.

Saving was omitted, as the res:// path is unavailable while exported

--------------------------------------------------------------------------------
   Running Rust benchmarks
--------------------------------------------------------------------------------
                                              min       median
   gdbin.rs:
   -- serialize                  ...      3.853μs      5.548μs
   -- deserialize                ...      7.514μs      9.500μs
   -- gdbin_load                 ...    120.190μs    177.116μs

   gdron.rs:
   -- serialize                  ...      5.105μs      6.051μs
   -- deserialize                ...      7.113μs      8.318μs
   -- gdron_load                 ...    140.451μs    205.902μs