CMake Output

The CMake format scans the output directory for *-rb.cpp files and generates:

flowchart LR
    subgraph Input
        CF["cmake-bindings.yaml"]
        S1["*-rb.cpp"]
    end

    CF & S1 --> RB["ruby-bindgen"]

    subgraph "CMake Output"
        C1["CMakeLists.txt"]
        C2["CMakePresets.json"]
    end

    RB --> C1 & C2

Project Files

When the project option is set, ruby-bindgen generates the root CMakeLists.txt and CMakePresets.json. When project is omitted, these files are not generated — only subdirectory CMakeLists.txt files are produced. This is useful when you want to create and manage the root project files yourself and only regenerate subdirectory files on subsequent runs.

Top-level CMakeLists.txt

The top-level CMakeLists.txt is a complete project file that configures the entire build:

• C++17 standard requirement
• Rice fetched from GitHub via FetchContent
• Ruby detection via find_package(Ruby)
• Library target (SHARED on MSVC, MODULE elsewhere)
• Extension output configuration (correct suffix, visibility settings)
• Subdirectory includes and *-rb.cpp source file listing

For a well-documented example, see the BitmapPlusPlus-ruby CMakeLists.txt. For details on how Rice uses CMake, see the Rice CMake documentation.

CMakePresets.json

The top-level directory also gets a CMakePresets.json with build presets for all major platforms. For an example, see the BitmapPlusPlus-ruby CMakePresets.json. For details, see the Rice CMakePresets.json documentation.

All presets use Ninja as the build generator and include appropriate compiler flags for each platform (visibility settings, debug info, optimization levels).

Subdirectories

Each subdirectory containing *-rb.cpp files gets a minimal CMakeLists.txt that lists its source files and any nested subdirectories:

ext/generated/
  CMakeLists.txt          # root project (requires project option)
  CMakePresets.json       # build presets
  core/
    CMakeLists.txt        # add_subdirectory("hal") + target_sources(...)
    matrix-rb.cpp
    image-rb.cpp
    hal/
      CMakeLists.txt      # target_sources(...)
      interface-rb.cpp

# Subdirectories
add_subdirectory("hal")

# Sources
target_sources(${CMAKE_PROJECT_NAME} PUBLIC
  "matrix-rb.cpp"
  "image-rb.cpp"
)