Tutorial 95: Speedy Blupi: A Real-World CNA Port

CNA — C++ XNA 4.0 reimplementation

The starting point

Speedy Blupi is a 2D action platformer from the Blupi game series by EPSITEC SA; the version that was ported is the 2013 Windows Phone edition, a C#/XNA 4.0 game with a tile-based world, multiple game modes, animated sprites and sound. Its original source code has not been publicly released. The CNA port is the OpenEggbert project’s openeggbert/mobile-eggbert repository (MIT-licensed, not part of the libcna organisation), whose README describes the route: the 2013 release was decompiled with ILSpy to C# source, that C# was migrated from XNA 4.0 to MonoGame, then rewritten from C# to C++, and finally moved from MonoGame to CNA. The C++ is a class-by-class rewrite of roughly 32,000 lines (at commit d43c6a1, 2026-08-21). It stands in here for the general shape of a 2D XNA/MonoGame game: SpriteBatch throughout, content loaded through ContentManager, touch and accelerometer input, and a custom tilemap renderer.

What the game code used

The XNA-style game code being carried across used: SpriteBatch for all 2D rendering, ContentManager.Load<Texture2D> for textures, SoundEffect and MediaPlayer for audio, GamePad, Keyboard and touch input, the Accelerometer, isolated storage for save games, and a custom tilemap renderer built on SpriteBatch.Draw calls. In the real C++ port these map onto CNA as getContentProperty().Load<Texture2D>(...) over loose PNG files under a Content/ directory, System::IO::IsolatedStorage for saves, and Microsoft::Devices::Sensors::Accelerometer (see Tutorial 50).

Where the real port stands

Consumer projects are evidence for their own revision only, so here is what the port’s repository and site show, without claiming more:

• Web: a WebAssembly (Emscripten) build is playable at speedyblupi.com/SpeedyBlupi2013. It embeds an early, pre-modularization CNA revision from May 2026 with the SDL_RENDERER backend — neither the alpha.1 tag nor the current development snapshot.
• Desktop: it builds from source (Linux with SDL_RENDERER; Windows builds are documented). No prebuilt binaries or GitHub releases are published, and the repository’s own TODO list names open issues (for example sound and fullscreen behaviour).
• Android: a Gradle/NDK project exists in the repository. No APK is published.

Nothing here is a CNA release of the game.

Porting process to CNA

1. Replace using Microsoft.Xna.Framework; with using namespace Microsoft::Xna::Framework;
2. Replace new SpriteBatch(GraphicsDevice) with std::make_unique<SpriteBatch>(getGraphicsDeviceProperty())
3. getContentProperty().Load<Texture2D>("name") can stay as-is (it returns the texture by value) — CNA's ContentManager reads .xnb, then CNA's own .cnb, then falls back to loose files. If you would rather drop the pipeline, construct directly: Texture2D("assets/name.png", gd) (a CNA extension)
4. Song and MediaPlayer need no replacement — MediaPlayer plays songs through the audio implementation's mixer (SDL3_mixer by default). Swapping to a looping SoundEffectInstance is an option, not a requirement
5. Replace List<T> with std::vector<T> or sharp-runtime's System::Collections::Generic::List<T> (whose count is getCountProperty(), not Count)
6. Replace null with nullptr, string with std::string
7. Replace (float)gameTime.getElapsedGameTimeProperty().getTotalSecondsProperty() with static_cast<float>(gt.getElapsedGameTimeProperty().getTotalSecondsProperty())
8. XACT AudioEngine / WaveBank / SoundBank now work directly in CNA (real .xgs/.xsb/.xwb parsing) — no replacement needed unless you prefer the simpler SoundEffect constructor API

API compatibility lessons

• Rectangle.Intersects() works identically in CNA and MonoGame — no changes needed
• Color constructor new Color(r,g,b,a) maps to Color(r,g,b,a) — identical. Two behaviours match real XNA in this snapshot: a default Color() is transparent black, and Color float construction saturates and rounds ties-to-even
• SpriteBatch.Draw overloads are matched shape-for-shape in CNA, with C++ types: the texture is a const Texture2D& and an optional source rectangle is a std::optional<Rectangle> — usually no changes to draw calls beyond dereferencing your texture pointer
• Vector2.Zero, Vector2.One are static members in CNA exactly as in XNA
• MathHelper.Clamp, MathHelper.Lerp behave identically
• GamePad.GetState(PlayerIndex.One) maps to GamePad::GetState(PlayerIndex::One) — identical semantics, but the state members are accessors (getIsConnectedProperty(), getButtonsProperty().getAProperty())

Content adaptation

You have two routes, and they can be mixed asset by asset.

Keep compatible .xnb files. CNA reads them through 61 built-in readers (60 without a native 128-bit integer) and a Game registers them when it is constructed; only a stand-alone ContentManager needs CNA::Internal::Xnb::RegisterAllBuiltInXnbReaders(). There is no reflection-based discovery, but custom ContentTypeReader<T> creators can be registered explicitly. Compiled effects additionally require a capable renderer build.

Or export to loose files. Export PNGs from the original XNB textures with the MonoGame Content Builder into an assets/ or Content/ directory. CNA decodes PNG (and JPG, BMP, GIF, TGA, TIF, QOI) with its own image loader, and ContentManager falls back to loose files when no .xnb or .cnb is present, so Load<Texture2D>("name") keeps working unchanged. You can also build .cnb or .xnb content from the sources with the build-time cna-content tool.

Custom shaders still need a deliberate portability decision. CNA can load XNA/FNA D3D9 Effect Framework binaries on FNA3D and on renderers whose compiled-effects build option is enabled (eight default-OFF options; a default configure reports the capability on FNA3D only), but the runtime does not compile HLSL .fx source or convert DXBC/MGFX (cna-content can compile .fx at build time through an external legacy fxc that you supply). Effects outside that compatible binary path must use the active renderer's ShaderEffect source or binary format. A purely 2D SpriteBatch game like this one is usually unaffected.

Key porting patterns

// Pattern 1: Convert content loading
// C# MonoGame:
//   texture = Content.Load<Texture2D>("Blupi/blupi");
// CNA C++ (the XNA way; Load<T> returns the texture by value):
//   Texture2D texture = getContentProperty().Load<Texture2D>("Blupi/blupi");
// or, dropping ContentManager (CNAEXT constructor that reads a file):
//   texture_ = std::make_unique<Texture2D>("assets/Blupi/blupi.png", gd);

// Pattern 2: Keep MediaPlayer, or convert Song to a looping SoundEffectInstance
// C# MonoGame:
//   MediaPlayer.Play(Content.Load<Song>("music/theme"));
//   MediaPlayer.IsRepeating = true;
// CNA C++, MediaPlayer route (properties become accessors; Play takes a Song*):
Song theme = getContentProperty().Load<Song>("music/theme");   // keep the Song alive while it plays (e.g. as a member)
MediaPlayer::setIsRepeatingProperty(true);
MediaPlayer::Play(&theme);
// CNA C++, SoundEffectInstance route (CreateInstance() returns the instance by value;
// set the loop flag BEFORE the first Play(), it cannot change afterwards):
SoundEffect music("assets/music/theme.ogg");
auto musicInst = music.CreateInstance();
musicInst.setIsLoopedProperty(true);
musicInst.Play();

// Pattern 3: Convert string interpolation to std::string
// C# MonoGame:
//   string path = $"sprites/{name}.png";
// CNA C++:
std::string path = "assets/sprites/" + name + ".png";

// Pattern 4: Convert foreach to range-for
// C# MonoGame:
//   foreach (var tile in tiles) tile.Draw(spriteBatch);
// CNA C++:
for (auto& tile : tiles_) tile.Draw(*spriteBatch_);

// Pattern 5: Convert nullable references to std::optional
// C# MonoGame:
//   Texture2D? overrideTexture = null;
// CNA C++ (Texture2D is a cheap shared handle, so hold it by value):
std::optional<Texture2D> overrideTexture_;    // empty == null

// Pattern 6: Convert C# events to sharp-runtime System::EventHandler<TEventArgs>
// C# MonoGame:
//   public event Action<int> OnScoreChanged;
// CNA C++ with sharp-runtime: the payload travels in an EventArgs subclass.
struct ScoreChangedEventArgs : System::EventArgs {
    SharpRuntime::intcs NewScore = 0;
};

System::EventHandler<ScoreChangedEventArgs> OnScoreChanged;

// Subscribe with += (the handler takes sender + args):
OnScoreChanged += [](System::Object* sender, const ScoreChangedEventArgs& e) {
    // react to e.NewScore
};

// Raise it (Invoke() is an alias for Raise()):
ScoreChangedEventArgs args;
args.NewScore = score_;
OnScoreChanged.Raise(this, args);

// Pattern 7 (no code): device services carry over almost by name.
//   WP7 IsolatedStorageFile      -> System::IO::IsolatedStorage (sharp-runtime), or XNA's StorageDevice
//   WP7 Accelerometer (events)   -> Microsoft::Devices::Sensors::Accelerometer, polled or via CurrentValueChanged