gdext-egui egui backend implementation for Godot 4

Example Godot project

See Gif of working example(Reddit link, 2.8MiB~)

Usage

In Cargo.toml, under the [dependencies] tab

godot = { git = "https://github.com/godot-rust/gdext", branch = "master" }
gdext-egui = { git = "https://github.com/kang-sw/gdext-egui", branch = "master" }

NOTE

If any API breakage from gdext master branch crate causes compilation error from this crate, you can add below line to Cargo.toml to make it compatible with current(2024-02-23 16:07:10) dependency version:

[patch.crates-io]
godot = { git = "https://github.com/godot-rust/gdext", rev = "6614030150950ffa6bd0311a2b914b86d5b7e9e9" }

In Rust, write a GodotClass derivative like this:

#[derive(GodotClass)]
#[class(init, base=Node)]
struct Showcase {
    base: Base<Node>,

    #[init(default = OnReady::manual())]
    egui: OnReady<Gd<gdext_egui::EguiBridge>>,

    demos: egui_demo_lib::DemoWindows,
}

#[godot_api]
impl INode for Showcase {
    fn ready(&mut self) {
        self.egui.init(gdext_egui::EguiBridge::new_alloc());

        // `EguiBridge` MUST be registered in scene tree to work properly!
        let mut gd_self = self.to_gd();
        gd_self.add_child(self.egui.clone().upcast());
        self.egui.set_owner(gd_self.upcast());
    }
    
    fn process(&mut self, _d: f64) {
        // If you hope to put UI code in main loop, you MUST get `egui::Context` 
        // via `EguiBridge::current_frame()` method!
        let ctx = self.egui.bind().current_frame().clone();
        self.demos.ui(&ctx);
    }
}

Unsafety

Bunch of unsafe blocks are used to implement drag and drop scheme between egui and godot native ui. Generally it is considered safe since both of godot native and

Features

• Window support
  • Basic Viewport
    • Creation / Disposal
    • Mouse Input Handling
      • Editor extension
      • In-editor viewport
    • Text Input / IME support
  • "GUEST MODE" Viewports
    • Spawn EGUI layer onto any existing window, other than root viewport.
  • Viewport Close Signal
  • Drag-n-Drop
    • <-> Godot Editor
    • <-> OS File System
• Rendering
  • Clipping
• Utilities
  • Expose GdScript API (Inherently, a class wrapper for frequently used methods)
  • Property display (for editor integration)

Limitations

• Editor Plugin is still under development.
• IME support is sub-optimal.