Orion is a retro-styled UI framework written in C that brings the familiar Windows API message-based architecture to modern cross-platform development. Extracted from DOOM-ED, it features a clean three-layer design modeled after classic Windows DLLs (USER, KERNEL, COMCTL), making it instantly recognizable to developers who’ve worked with Win32. Built on SDL2 and OpenGL 3.2+, Orion delivers hardware-accelerated rendering with a nostalgic bitmap font aesthetic reminiscent of DOS and early Windows interfaces. The framework provides a complete set of common controls (buttons, checkboxes, edit boxes, lists, combo boxes, and a console) all following message-driven patterns that feel both vintage and powerful. Perfect for game tools, retro-style applications, or anyone who misses the simplicity and directness of classic GUI programming.

filemanager.c example:

helloworld.c example:

Directory Structure

ui/
├── ui.h              # Main header that includes all UI subsystems
├── user/             # Window management and user interface (USER.DLL equivalent)
│   ├── user.h        # Window structures and management functions
│   ├── messages.h    # Window message constants and macros
│   ├── draw.h        # Drawing primitives (rectangles, icons)
│   ├── text.h        # Text rendering functions
│   ├── text.c        # Text rendering implementation (small font, DOOM/Hexen fonts)
│   ├── window.c      # Window management implementation
│   ├── message.c     # Message queue implementation
│   └── draw_impl.c   # Drawing primitives implementation
├── kernel/           # Event loop and SDL integration (KERNEL.DLL equivalent)
│   ├── kernel.h      # Event management and SDL initialization
│   ├── renderer.h    # Renderer API - OpenGL abstraction
│   ├── renderer_impl.c # Renderer API implementation
│   ├── renderer.c    # Sprite rendering implementation
│   ├── event.c       # Event loop implementation
│   ├── init.c        # SDL initialization
│   └── joystick.c    # Joystick/gamepad support
└── commctl/          # Common controls (COMCTL32.DLL equivalent)
    ├── commctl.h     # Common control window procedures
    ├── button.c      # Button control implementation
    ├── checkbox.c    # Checkbox control implementation
    ├── edit.c        # Text edit control implementation
    ├── label.c       # Label (static text) control implementation
    ├── list.c        # List control implementation
    ├── combobox.c    # Combobox (dropdown) control implementation
    ├── console.c     # Console control implementation
    ├── columnview.h  # ColumnView control header
    ├── columnview.c  # Multi-column item view implementation
    ├── menubar.h     # Menu bar control header
    ├── menubar.c     # Horizontal menu bar implementation
    └── terminal.c    # Lua script terminal implementation

Architecture

Orion follows a layered architecture similar to Windows:

ui/user/ - Window Management Layer

Handles window creation, destruction, message passing, and basic rendering primitives.

Key Components:

• Window structure (window_t)
• Window creation and lifecycle management
• Message queue and dispatch
• Drawing primitives (rectangles, text, icons)
• Window messages (evCreate, evPaint, evLeftButtonUp, etc.)

ui/kernel/ - Event Management Layer

Manages the SDL event loop and translates SDL events into window messages. Also provides the Renderer API for OpenGL abstraction.

Key Components:

• SDL initialization
• Event loop (get_message, dispatch_message)
• Global state (screen dimensions, running flag)
• Renderer API: High-level OpenGL abstraction (R_Mesh, R_Texture, R_MeshDrawDynamic)

ui/commctl/ - Common Controls Layer

Implements standard UI controls that can be used to build interfaces.

Available Controls:

• Button: Clickable button with text label
• Checkbox: Toggle control with checkmark
• Edit: Single-line text input control
• Label: Static text display
• List: Scrollable list of items
• Combobox: Dropdown selection control
• Console: Message display console with automatic fading and scrolling
• ColumnView: Multi-column item view with icons, colors, and double-click support
• MenuBar: Horizontal menu bar with dropdown menus
• Terminal: Interactive Lua script terminal with input/output

Building

Orion supports Linux, macOS, and Windows platforms.

Dependencies

Linux (Ubuntu/Debian):

sudo apt-get install liblua5.4-dev libsdl2-dev libgl1-mesa-dev libcglm-dev

macOS:

brew install sdl2 cglm lua

Windows (MSYS2/MinGW64):

pacman -S mingw-w64-x86_64-gcc mingw-w64-x86_64-make mingw-w64-x86_64-SDL2 mingw-w64-x86_64-lua mingw-w64-x86_64-cglm make

Build Commands

# Build library (static and shared)
make library

# Build examples
make examples

# Build and run tests
make test

# Clean build artifacts
make clean

Build Output

• Linux: build/lib/liborion.a, build/lib/liborion.so
• macOS: build/lib/liborion.a, build/lib/liborion.dylib
• Windows: build/lib/liborion.a, build/lib/liborion.dll
• Examples/Tests: build/bin/

Window Messages

The framework uses a message-based architecture. Common messages include:

• evCreate - Window is being created
• evDestroy - Window is being destroyed
• evPaint - Window needs to be redrawn
• evLeftButtonDown - Left mouse button pressed
• evLeftButtonUp - Left mouse button released
• evKeyDown - Key pressed
• evKeyUp - Key released
• evCommand - Control notification