GT4Recomp

GT4Recomp is a static recompilation of Gran Turismo 4 (NTSC-U, SCUS-97328) for Windows x86-64. The game's own code is translated ahead of time into C++ and compiled to native machine code; the PS2 hardware it talks to is reproduced in software, and graphics run on Vulkan. Nothing generates code while the game runs, which is also what makes future Android and iOS builds possible.

Highlights

• Locked 60 FPS at 100% game speed in every scene we test, with a frame every 16.7 ms.
• All game code is precompiled: the main CPU (EE) and every VU1 and VU0 microprogram run as native code, with no interpreter on the normal path.
• Sharp, high-resolution image: 1080p out of the box, with 1440p, 4K and 8K available. The game is rendered at that resolution, not just stretched, with borderless fullscreen.
• Native ultrawide and any aspect ratio (1.1.0): 21:9, 32:9, 16:10 or a phone shape, automatic from the output resolution. The 3D view widens Hor+/Vert+, the HUD stays centred 16:9 and menus are pillarboxed; the internal resolution follows automatically, with a Render scale of 50-200%.
• GSdx renderer (the PCSX2 GS) in its own process: crisp deinterlaced menus, every GSdx option in the launcher and a built-in performance overlay. CoreGS 2.0, our own renderer, is in development.
• Custom texture packs: drop a pack's files straight into the data\Textures folder of your GT4Recomp install (Settings > Graphics > Open textures folder); Load custom textures is on by default. HD textures and mods from the PCSX2 community work without renaming folders.
• Crash-safe memory card: saves survive a crash or a forced close.
• Release 1.2.1: a one-click installer and a launcher that sets the game up from your own disc image, with settings, saves, controller remapping and update checks.
• Any controller through SDL3 (Xbox, DualShock 4, DualSense, Switch Pro...) and a modern keyboard layout.

Performance

Every tested scene holds 60 FPS at 100% game speed on the GSdx renderer (Ryzen 7 5700X + Radeon RX 9060 XT):

Scene	FPS	Game speed	Frame pacing
Time Trial · Nordschleife · Toyota Supra	60	100%	16.7 ms flat
Arcade race · Nordschleife · 5 AI cars	60	100%	16.7 ms flat
Night race · 5 AI cars	60	100%	16.7 ms flat
Rally · Grand Canyon	60	100%	16.7 ms flat
Car showroom	60	100%	16.7 ms flat

How we got here: the first native build ran at 30 FPS and 51% speed. Compiling the VU1 microcode ahead of time, submitting GPU work asynchronously and pacing every frame from a single clock brought it to a steady 60 FPS at full speed. Release 1.2.2 batches the work handed to the VU1 thread and the graphics process, so the night race needs about 2 ms less CPU time per frame.

Known issues

• Some license demos and menu backgrounds do not play; every license test is playable. This matches PCSX2 with default settings (why).
• Racing wheels are not supported yet, and long sessions are not fully qualified.
• Menus, movies and photo mode stay 16:9 (pillarboxed) at other aspect ratios; split screen and photo mode in ultrawide have had little testing.
• The installer is not code-signed: Windows SmartScreen may warn on the first start ("More info", "Run anyway").
• Most testing was on an AMD GPU; NVIDIA and Intel GPUs have had less testing.

Roadmap

Phase	Release	Platform	Renderer	Status
1	1.x	Windows PC	GSdx (PCSX2 GS, separate process)	Done (1.0.0; current 1.2.0)
2	2.0.0	Windows PC	CoreGS 2.0 (our own renderer) as the default · GSdx as the fallback	In progress
3	after 2.0.0	Linux (native)	CoreGS 2.0	Planned
4	after 2.0.0	Android	CoreGS 2.0 (Vulkan)	Planned

Phases 3 and 4 start once CoreGS 2.0 is ready and GT4Recomp 2.0.0 is out.

Every piece of work is a numbered task in TASKS.md, tested in game before it is merged.

How it works

The EE game code is translated ahead of time into C++ and compiled for x86-64. The VU1 microcode, stored encrypted inside the executable, is recovered and compiled offline (all 2,048 entry points), verified against a reference interpreter on real game state; the 14 VU0 microprograms are compiled the same way. IOP system services are native. Frames are paced by one high-resolution clock with rate-controlled audio. This is a hybrid recompilation: PS2 hardware is still modeled in software, so we do not claim zero emulation or full PS2 fidelity. Details: Architecture.

Requirements

• Windows 10 or 11, 64-bit.
• A processor with SSE4.1 (Intel Core i3/i5/i7 / AMD FX or newer).
• A graphics card with Vulkan 1.2 and current drivers (NVIDIA, AMD or Intel).
• Your own disc image of Gran Turismo 4 USA v2.00 (SCUS-97328) as a plain .iso.
• About 6 GB free: the launcher keeps a copy of your disc image (5.3 GB) next to the program.

The launcher checks the processor and Vulkan before setup and before Play, and says what is missing.

Install

1. Download GT4Recomp-Setup-1.2.5.exe from Releases and run it. It installs to C:\Program Files\GT4Recomp by default (Windows asks for administrator approval), or to any folder or drive you choose. If the Microsoft Edge WebView2 Runtime is missing (Windows 10), the installer downloads it from Microsoft.
2. Start Gran Turismo 4 from the Start menu and choose your disc image. The launcher copies and checks it and downloads the GSdx renderer, which runs the game (the game needs GSdx and does not start without it).
3. Press Play.

Everything large stays together in the install folder, in data (the copy of your disc image, GSdx, custom textures and logs), so the whole folder can be moved or copied to another drive and still works. Your settings, saves and replays are per Windows user in %APPDATA%\GT4Recomp, and the uninstaller keeps them unless you tick the box. Updates from the launcher install silently after one Windows approval and reopen the launcher. Coming from 1.2.0, the first start moves your files to these places (copied and checked; the old Documents folder is renamed, never deleted). This repository does not include game files, disc images, BIOS dumps or save files. Building from source needs your own game files and a development environment: see the Build guide.

Controls

Controllers (Xbox, DualShock 4, DualSense, Switch Pro and others, through SDL3) work out of the box, mapped to the DualShock 2 layout, and can be remapped in the launcher (Settings > Controls).

Controller	PS2	Notes
A · B · X · Y (Cross · Circle · Square · Triangle on PlayStation pads)	Cross · Circle · Square · Triangle	Face buttons
LB · RB	L1 · R1
LT · RT	L2 · R2	Analog triggers with pressure, for progressive throttle and brake
Left / right stick	Left / right analog stick	With dead zones; L3 · R3 on stick click
D-pad	D-pad
Start · Back	Start · Select

The keyboard has a fixed layout:

Key	Action (PS2 button)
W · Enter	Accelerate, confirm (Cross)
S	Brake (Square)
Space	Handbrake (Circle)
A · D · arrow keys	Steer, navigate (D-pad); E is also D-pad up
Backspace · Esc	Back (Triangle)
Shift	Nitro (R1)
R · F	Gear up · gear down (R2 · L2)
Q	Look back (L1)
C · Tab	Camera (Select)
P	Start / Pause
Alt+Enter, F11	Borderless fullscreen

Support and contributing

Want to help? Contribute to the development or donate: tokens are expensive, and they are what make this project possible.

• Donate: ko-fi.com/moesuito. Donations pay for the AI development tools behind GT4Recomp, starting with the plan that keeps CoreGS 2.0 and the next updates moving.
• Contribute: read CONTRIBUTING.md for the rules and the pull request template, then pick a task from TASKS.md or an issue.
• Report bugs: open an issue with the launcher log (Settings > About > Open log folder).
• Talk with us: join the GT4Recomp Discord server.

Credits

Project	Author	What it gives this project
ps2-web-recomp (MIT)	snuri00	The runtime foundation: EE-to-C++ translator, PS2 hardware models, the GS compute renderer and the original VU1 compiler.
gt4-decomp (MIT)	gustavocanepa	GT4's decompilation: function names, class layouts and engine notes (identity).
Nenkai's GT research	Nenkai	File formats and the VU1 microcode encryption scheme (details).
GT4FS	Razer2015	GT4 volume file-system research.
PCSX2 (GPL-3.0)	PCSX2 team	Decades of PS2 knowledge; its GS runs only in the separate gt4-gs.exe.
naga · Vulkan-Headers	gfx-rs · Khronos	Shader compilation at build time · Vulkan API headers.

Exact revisions and licenses: THIRD_PARTY.md.

License and legal

• GT4Recomp's own code is MIT. The game executable does not contain or link GPL code; the PCSX2 GS (GPL-3.0-or-later) runs only in the separate gt4-gs.exe, built from moesuito/gt4recomp-gs with its source published on each release.
• You bring your own disc. The project does not include Gran Turismo 4, disc images, BIOS files, keys or saves.
• "Gran Turismo" and "PlayStation" are trademarks of Sony Interactive Entertainment. Gran Turismo 4, its logos and artwork belong to Sony Interactive Entertainment and Polyphony Digital. GT4Recomp is an unofficial fan project, not affiliated with or endorsed by either.

Documentation

TASKS · CONTRIBUTING · STATUS · BUILD · ARCHITECTURE · Renderers · Release 1.0.0 plan · Decisions · Journal