BongoCat: a C, SDL3 and OpenGL desktop pet that reacts to your keyboard

What BongoCat actually is, and who it is for

BongoCat is a desktop pet: a small application that draws an animated character on your screen. The repository describes it as "C × SDL3 × OpenGL", and the topics list confirms the stack (bongo-cat, c, opengl, sdl3, pet-project). It is not a library you embed in another program and it is not a service. It is an executable you run.

The audience is narrow and specific. This is a project for people who are comfortable compiling a C and C++ codebase, because the README's main content is a build guide. It is also for users who want a downloadable binary: the README points to the Microsoft Store listing and to GitHub Releases, and the homepage bongocat.pet links to a model gallery. If you are looking for a configurable tool with a documented settings file, the README does not provide one.

The licensing is worth noticing early. The repository ships AGPL-3.0 as LICENSE, plus a separate LICENSE-MIT file, and the README badge marks AGPL-3.0. That combination matters if you plan to redistribute a modified build.

How the C, SDL3 and OpenGL stack fits together

The mechanism visible in the repository is a conventional native application layout. The top level holds CMakeLists.txt, include/, src/, tests/, cmake/, resources/ and packaging/. Dependencies are resolved at configure time: the README states that SDL3, yyjson, stb, miniaudio and Nuklear are downloaded by default, which is what the BONGO_CAT_FETCH_DEPS option controls.

The rendering path is OpenGL, and the optional character runtime is Live2D through the Cubism SDK for Native. That is the interesting part of the architecture, and also the sharpest edge. If the SDK is absent, the README says CMake emits a warning and builds a diagnostic backend, and it states plainly that this backend "is intended for startup and platform diagnostics; it does not provide Live2D model rendering." In other words, a default build without the SDK can start and report platform information, but it will not draw the cat you saw in the demo video.

The support libraries tell you what the application does beyond drawing. Nuklear is an immediate-mode GUI toolkit, so some in-app interface is drawn rather than loaded from a UI file. miniaudio handles sound. yyjson parses JSON, which is the likely format for model or configuration data, although the README does not document the schema. stb covers image decoding. None of this is spelled out in prose in the README; it is inferred from the dependency list and the directory layout, and the README is silent on how these pieces connect at runtime.

Building bongo cat from source on Linux, macOS and Windows

The README gives build steps rather than usage steps. The prerequisites are a C11 compiler, a C++17 compiler, CMake 3.24 or newer, and desktop OpenGL development files. The first configuration needs network access because dependencies are fetched. Run the commands from the project root, the directory containing CMakeLists.txt.

On Debian or Ubuntu, install the toolchain and the OpenGL and X11 headers first:

sudo apt-get update
sudo apt-get install -y build-essential cmake ninja-build \
  libgl1-mesa-dev libx11-dev libxi-dev libxfixes-dev

Then configure and build with a single-configuration generator. The README uses Ninja on Linux and macOS:

cmake -S . -B build -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DBONGO_CAT_FETCH_DEPS=ON
cmake --build build --parallel

The executable lands at build/BongoCat on Linux and at build/BongoCat.app/Contents/MacOS/BongoCat on macOS. On Windows the README requires Visual Studio 2022 with the Desktop C++ workload, and notes that MinGW can build the diagnostic backend but is not supported for the Cubism SDK:

cmake -S . -B build -G "Visual Studio 17 2022" -A x64 `
  -DBONGO_CAT_FETCH_DEPS=ON
cmake --build build --config Release --parallel

That produces build/Release/BongoCat.exe. CTest targets are enabled by default, so you can check the build:

ctest --test-dir build --output-on-failure

For a multi-configuration generator, the README shows ctest --test-dir build -C Release --output-on-failure instead.

The Cubism SDK gap between a working build and a rendering cat

The most concrete limitation in the README concerns Live2D. A successful build is not the same as a working pet. Without a compatible Cubism SDK for Native, you get the diagnostic backend. The README is explicit that this backend does not render Live2D models, so the visual result of a default build differs from the demo video in the repository.

To get the full runtime, the SDK must be installed and either placed at vendor/CubismSdkForNative or passed explicitly:

cmake -S . -B build -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DBONGO_CAT_CUBISM_SDK=/path/to/CubismSdkForNative \
  -DBONGO_CAT_REQUIRE_CUBISM=ON

The README states that the SDK must contain its Core library, Framework sources, and the OpenGL GLEW third-party tree in the layout expected by cmake/Cubism.cmake. That is a strict directory contract, and cmake/Cubism.cmake is the file to read if configuration fails. Setting BONGO_CAT_REQUIRE_CUBISM=ON makes configuration fail instead of silently selecting the diagnostic backend, which is the right default for anyone shipping a build and the wrong one for someone who just wants to compile quickly.

The second gap is documentation. The README covers prerequisites, configuration, tests and the optional SDK, and stops there. There is no section on configuring the pet, no plugin interface, no CLI flags, and no description of how input from your keyboard or mouse reaches the animation. The related searches around a bongo cat keyboard or an OBS plugin describe things this README does not document, so treat those as unverified for this repository.

How BongoCat differs from web-based desktop pets

The obvious alternative class is a web-technology desktop pet: an Electron or similar shell that renders a character with HTML and CSS or a canvas, and that usually ships a JavaScript plugin API and a settings UI. The difference in approach is not cosmetic. A web shell gives you a documented extension surface and easier packaging, at the cost of a browser runtime and its memory footprint. BongoCat takes the opposite route: a C core, SDL3 for windowing and input, OpenGL for drawing, and Nuklear for any in-app interface.

That choice has consequences you can see in the build instructions. You need a C11 compiler, a C++17 compiler, CMake 3.24 or newer, and OpenGL development headers, and on Linux you install libgl1-mesa-dev, libx11-dev, libxi-dev and libxfixes-dev before anything compiles. A web-based pet typically needs none of that. In exchange, BongoCat's runtime does not carry a browser, and its dependency set (SDL3, yyjson, stb, miniaudio, Nuklear) is small and fetched at configure time.

The trade is extension versus footprint. If your goal is to write a plugin that changes behaviour, the web-based approach is the better fit because the extension surface is a first-class part of those projects. If your goal is a small native process that draws a character and plays sound, BongoCat's stack is the more direct one. The README does not describe a plugin system for BongoCat, so anyone expecting one should not assume it exists.

Release cadence, licence and the cost of upgrading

The repository is not archived, and the last push was on 2026-09-16. Releases are frequent: v1.4.0 on 2026-09-02, v1.7.0 on 2026-09-09, and v1.8.0 on 2026-09-11. Three releases in nine days is a fast cadence, and it is worth reading it as a signal about stability rather than as a promise. A project moving this quickly can rename a CMake option or change a vendor path between versions.

That is the real upgrade cost here. Your build depends on option names such as BONGO_CAT_FETCH_DEPS, BONGO_CAT_CUBISM_SDK and BONGO_CAT_REQUIRE_CUBISM, on the vendor/CubismSdkForNative location, and on the layout expected by cmake/Cubism.cmake. Any of those can change, and because dependencies are fetched at configure time, a rebuild also pulls whatever versions the configuration requests. Pin your build to a release tag rather than tracking main if you need reproducibility.

On licensing, the repository contains an AGPL-3.0 LICENSE, a separate LICENSE-MIT file, and a PRIVACY.md. The README badge marks the project AGPL-3.0. AGPL-3.0 carries network-use obligations that permissive licences do not, and the presence of two licence files means you should read both before redistributing a modified binary. This is not legal advice; the point is that the licence is not a formality for a project you might repackage.

Editorial conclusion

Adopt BongoCat if you want a small native desktop pet you are willing to build from source with CMake 3.24 or newer, and if AGPL-3.0 fits how you intend to distribute it. Do not adopt it if you need a documented plugin API, a scripting layer, or a packaged Linux binary, because the README documents none of those. Verify first that a compatible Cubism SDK for Native is available to you, since without it CMake falls back to a diagnostic backend that the README says does not render Live2D models.

Frequently asked questions

Official sources

1. License: AGPL-3.0
2. Project website
3. README
4. Releases
5. vladelaina/BongoCat on GitHub