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The Fern UI Framework is designed to run on multiple platforms with native rendering backends. The framework uses platform detection at compile-time to select the appropriate renderer implementation.

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Supported Platforms

Linux

Production-ready support via X11

Web/WASM

WebAssembly support via Emscripten

macOS

Planned support (implementation exists)

Windows

Planned support (not yet implemented)

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Platform Detection

Fern uses CMake preprocessor definitions to detect the target platform at compile-time:
CMakeLists.txt:13-27
if(EMSCRIPTEN)
    set(PLATFORM_NAME "Web")
    add_definitions(-D__EMSCRIPTEN__)
elseif(APPLE)
    set(PLATFORM_NAME "macOS")
    add_definitions(-D__APPLE__)
elseif(UNIX AND NOT APPLE)
    set(PLATFORM_NAME "Linux")
    add_definitions(-D__linux__)
elseif(WIN32)
    set(PLATFORM_NAME "Windows")
    add_definitions(-DWIN32)
else()
    message(FATAL_ERROR "Unsupported platform")
endif()

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Platform Renderer Factory

The framework uses a factory pattern to instantiate the correct renderer based on compile-time platform detection:
platform_factory.cpp:16-28
std::unique_ptr<PlatformRenderer> createRenderer() {
#ifdef __EMSCRIPTEN__
    return std::make_unique<WebRenderer>();
#elif defined(__APPLE__)
    // Extern function defined in macos_renderer.mm
    extern std::unique_ptr<PlatformRenderer> createMacOSRenderer();
    return createMacOSRenderer();
#elif defined(__linux__)
    return std::make_unique<LinuxRenderer>();
#else
    #error "Only Web, macOS, and Linux platforms supported currently"
#endif
}

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Platform-Specific Source Files

Each platform has its own renderer implementation: 
src/cpp/src/platform/linux_renderer.cpp
The platform factory (platform_factory.cpp) conditionally includes only the relevant renderer based on compilation flags.

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Build System Support

Fern provides multiple build options:

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CMake Build

The primary build system uses CMake to detect platforms and configure compilation: 
mkdir build && cd build
cmake ..
cmake --build .

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Shell Script Build

For quick builds on Linux and Web, use the provided build script:
build.sh
./build.sh linux          # Build for Linux
./build.sh web            # Build for Web/WASM
./build.sh all            # Build for all platforms

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Fern CLI

For Web development with live reload: 
./fern-cli.sh example.cpp --port 8000

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Platform Renderer Interface

All platform renderers implement the PlatformRenderer interface, which provides:
  • Initialization: initialize(width, height)
  • Rendering: present(pixelBuffer, width, height)
  • Event handling: Mouse, keyboard, resize callbacks
  • Window management: setTitle(), setSize(), shouldClose()
  • Event polling: pollEvents()
The Web platform uses event listeners instead of polling, while native platforms (Linux, macOS) use event polling in the main loop.

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Next Steps

Linux Setup

Learn about X11 dependencies and Linux-specific configuration

Web/WASM Setup

Compile to WebAssembly with Emscripten

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