Godot UI Markup Language

GUML is a declarative UI markup language (.guml) for Godot .NET, providing a QML/XAML-like development experience. It allows developers to define UI components and layouts using a concise syntax, with support for data binding, event handling, and reusable components. GUML uses Roslyn Source Generator for compile-time code generation, delivering maximum performance with zero runtime overhead.

Features

• QML-like declarative syntax
• Data binding — automatically update UI when controller properties change (one-way :=, two-way <=>, reverse =:)
• Event wiring — connect Godot signals and C# events with one line
• List rendering — each blocks with incremental updates via ObservableCollection<T>
• Reusable components — compose and reuse .guml files with typed parameters
• Full Godot UI component support (all built-in Control types)
• Theme overrides — set theme styles directly in GUML
• Source Generator mode — compile-time code generation for maximum performance

Install

dotnet add package GUML

For source generator support:

dotnet add package GUML.SourceGenerator

Documentation

• Documentation Hub — guides, reference, and API docs
• Quick Start — install GUML, write your first .guml file, run it in Godot
• GUML Syntax — full syntax reference

Language Specification

The formal GUML language specification is available in the GUMLSpec directory. It covers:

• Lexical structure & grammar (BNF)
• Types, expressions, and directives
• Component model and controller integration
• Code generation and API interface specifications
• Diagnostics

IDE Support

Editor plugins have been moved to their own repositories:

Editor	Repository
VS Code	GUML.VSC
JetBrains Rider	GUML.Rider

Project Structure

Directory	Description
GUML	Core runtime library — GuiController, converters, bindings
GUML.Shared	Shared infrastructure — full-fidelity CST parser, API metadata models, diagnostics
GUML.SourceGenerator	Roslyn source generator for compile-time .guml → C# code generation
GUML.Analyzer	Language analyzer CLI tool — Roslyn-based project analysis and LSP features via JSON-RPC
GUMLSpec	Formal language specification
Doc	User documentation (guides, reference, quick start)
TestApplication	Sample Godot project demonstrating GUML usage

Example

main.guml:

Panel {
    size: vec2(640, 480),
    theme_overrides: { 
        panel: style_box_flat({
            bg_color: color(0.4, 0.4, 0.4, 0.4)
        })
    },
    Label {
        position: vec2(10, 10),
        size: vec2(200, 30),
        // $controller.SayHello binding to Label.text.If SayHello changes, text will also change.
        text:= "hello " + $controller.SayHello
    }
    
    Button {
        position: vec2(10, 50),
        size: vec2(200, 30),
        text: "Change world",
        #pressed: $controller.ChangeHelloBtnPressed
    }
}

MainController.cs:

public class MainController : GuiController
{
    public string SayHello {
	    get => _sayHello;
		set
		{
			_sayHello = value;
			OnPropertyChanged();
		}
    }
	
    private string _sayHello = "world!";

	public void ChangeHelloBtnPressed()
	{
		SayHello = "new world!";
	}
}

After clicking the change world button, the text will change to hello new world!

License

MIT