Harry Potter and the Chamber of Secrets — GameCube Static Recompilation

HPCOS GC — an experimental native static-recompilation project for Harry Potter and the Chamber of Secrets on Nintendo GameCube.

Important

Work in progress. No original disc image or extracted copyrighted game data is distributed by this repository. You must supply your own legally obtained copy of the game.

Overview

HPCOS GC targets the North American GameCube release of Harry Potter and the Chamber of Secrets (GHSE69).

The project uses the ExpansionPak GameCube/Wii recompilation stack, with DolRecomp for ahead-of-time PowerPC recompilation and ModernGekko for the native runtime.

The goal is to run the original GameCube executable as statically recompiled native code while preserving the behaviour of the original game and progressively adding PC-oriented improvements in the runtime.

Current status

The game currently reaches and runs:

• title and menu flow
• loading screens
• in-game scenes and normal gameplay
• audio
• controller input
• save/runtime state
• Vulkan rendering through ModernGekko/Dolphin

The current native build targets the original NTSC game timing.

PC enhancements

In-game PC settings menu

Press Ctrl+F10 while the game is running to open the native HPCOS PC settings overlay. The normal F10 Dolphin pause hotkey is kept separate.

The overlay currently exposes live controls for:

• internal rendering resolution from native 1x through 12x
• V-Sync and the FPS performance overlay
• original 4:3, automatic host aspect, 16:9, 16:10, 21:9 and 32:9 modes
• horizontal FOV override, synchronized with the GHSE69 guest camera/frustum
• high-rate game VI/render target (60/90/120/144/165/240) with gameplay/physics held at native ~59.94 Hz
• optional host presentation FPS cap
• keyboard + mouse input merged with the normal GameCube controller on Port 1
• mouse sensitivity and Y-axis inversion
• direct in-menu keyboard/mouse rebinding
• runtime volume and mute controls

Settings and custom bindings are persisted in HPCOS_PC.ini inside the runtime configuration directory.

Default keyboard/mouse bindings are WASD for movement, mouse movement for the C-stick/camera, left/right/middle mouse for A/B/Z, E/Q for X/Y, Left Shift/Left Ctrl for L/R, Enter for Start and the arrow keys for the D-pad. Gamepad input remains enabled at the same time.

Note

The menu has two separate FPS controls. Game FPS raises the guest VI/render cadence without changing Dolphin's global emulation speed. GHSE69's phase-1 gameplay/physics update (0x80038DAC) is separately scheduled at the native ~59.94 Hz, while DSP/audio and CoreTiming remain on their normal clock. Presentation FPS cap only limits host presentation. Above 60 FPS the renderer currently presents the latest fixed simulation state between updates; true motion interpolation is a separate refinement.

Dynamic widescreen

HPCOS includes a runtime widescreen implementation rather than relying on a fixed 16:9 game patch.

The projection is adjusted dynamically from the actual host aspect ratio, allowing the 3D view to adapt to displays such as:

• 16:9
• 16:10
• ultrawide aspect ratios
• other window aspect ratios

For wider displays the 3D projection uses a Hor+ style adjustment instead of simply stretching the original 4:3 image.

Enable it with:

./run.sh --widescreen

Configurable FOV

A horizontal FOV can be selected at launch:

./run.sh --widescreen --fov 110

--fov represents the requested horizontal field of view.

The runtime synchronizes the corresponding game-side camera/frustum FOV used by GHSE69. The previous generic host perspective-FOV override has been removed: that layer also affects auxiliary perspective passes such as shadow cameras and could make shadows disappear when a custom FOV was active.

Dynamic widescreen also synchronizes all three GHSE69 aspect globals used by the original game's 16:9 patch. This makes the guest frustum/culling use the expanded aspect instead of keeping a hidden 4:3 visibility window, reducing objects popping out near the left and right edges.

XFB / presentation correction

The presentation path includes an XFB crop used to remove the original overscan-style bordering and make better use of the host window while preserving the dynamically corrected aspect ratio.

HUD behaviour

The 3D projection and orthographic paths are handled separately so increasing the world aspect ratio does not simply stretch the HUD together with the scene.

Static recompilation and runtime work

HPCOS is not just a wrapper around an emulator.

The original GameCube PowerPC code is processed by DolRecomp and translated ahead of time into native code that executes through the ModernGekko runtime.

Project-specific work currently includes:

• PowerPC static recompilation fixes and runtime integration
• optimized generated-code dispatch paths
• SMC / recompilation runtime optimizations
• optimized PowerPC emitter paths
• direct handling of common guest execution cases
• GameCube memory/MMIO/runtime integration
• guest-side camera/FOV synchronization
• host-side projection and presentation changes

The focus is to keep the recompiled execution path as native and lightweight as possible while retaining compatibility with the original GameCube software.

Screenshots

Title screen	Continue menu
Loading screen	Entrance hall
Castle yard	Harry with his wand

Build layout

The checked-in project deliberately keeps the files required to reproduce or run the current port:

.
├── build.sh                  # configures/builds ModernGekko + DolRecomp + the GHSE69 module
├── run.sh                    # launches the published runtime/module
├── ModernGekko/              # source tree consumed by build.sh
├── DolRecomp/                # recompilation source/tooling
├── recomp/                   # HPCOS recompilation source/output
├── runtime/                  # published moderngekko-run + Sys runtime data
├── module/                   # published gGHSE69_recomp.so + build info
├── docs/screenshots/         # project screenshots
├── build/                    # local CMake/Ninja build directory — ignored
├── port-build/               # intermediate port build — ignored
├── extracted/                # user-supplied original game files — ignored
└── user/                     # local runtime profile/saves/configuration — ignored

build.sh validates the GHSE69 main.dol, configures ModernGekko with CMake/Ninja, builds moderngekko-run, moderngekko-port and dolrecomp, builds the recompilation module, then publishes the runnable outputs into runtime/ and module/.

run.sh launches:

• runtime/moderngekko-run
• module/gGHSE69_recomp.so
• the user's local extracted/ game directory
• a local user/ runtime directory

Building

Requirements include CMake, Ninja, a supported C/C++ toolchain and the dependencies required by ModernGekko/DolRecomp.

The current build script supports the c and llvm recompilation backends and clang, gcc or automatic toolchain selection.

./build.sh

Examples:

BACKEND=c TOOLCHAIN=clang ./build.sh
BACKEND=llvm TOOLCHAIN=clang ./build.sh

The build expects your legally obtained game extraction at:

extracted/sys/main.dol

The expected target is GHSE69; build.sh verifies the DOL before building.

Running

Basic launch:

./run.sh

Dynamic widescreen:

./run.sh --widescreen

Dynamic widescreen with a custom horizontal FOV:

./run.sh --widescreen --fov 110

Experimental 120 FPS VBI target:

./run.sh --widescreen --fov 110 --fps 120

The current launcher uses Vulkan and Wayland.

Experimental project

HPCOS GC is still under active development.

Rendering, recompilation accuracy, performance and game compatibility may change as the static recompilation runtime continues to be investigated and optimized.

The project does not currently provide an unlocked-framerate implementation; the original NTSC game timing is intentionally preserved.

What is intentionally ignored

The .gitignore is intentionally conservative. It ignores things that should not be part of the repository, including reproducible build directories, caches, release staging, user-specific Dolphin/ModernGekko state, logs and original game files supplied by the user.

Original game data must never be committed.

Credits and acknowledgements

HPCOS GC depends on open-source work from the GameCube/Wii recompilation and emulation communities.

ExpansionPak

• DolRecomp — static PowerPC recompiler used by GameCube/Wii recompilation projects
  https://github.com/ExpansionPak/DolRecomp
• ModernGekko — runtime and tooling used to execute recompiled GameCube/Wii code
  https://github.com/ExpansionPak/ModernGekko

Upstream acknowledgements

ModernGekko credits and builds on work including:

• SpecialK / aharonahdoot — RecompCore
• The Dolphin Team — Dolphin and the GameCube/Wii hardware/runtime knowledge base
• Literally God / MrPoloGit — recompilation template/macOS work credited upstream

Please consult the upstream repositories, contributor histories and license files for complete and authoritative attribution.

Legal

This is an unofficial research/fan project and is not affiliated with or endorsed by Electronic Arts, Warner Bros., Nintendo, ExpansionPak, or the original developers.

No original disc image or extracted copyrighted game assets are distributed by this repository. Users must provide their own legally obtained game data.

License

See LICENSE for HPCOS-specific repository content.

Third-party components, including DolRecomp, ModernGekko and their dependencies, remain subject to their respective licenses.