GP2 Workshop

A cross-platform editor/patcher for Grand Prix 2's GP2.EXE. It edits the 24 per-slot "magic data" tuning tables and a curated set of statically-patchable physics values (engine, power curve, aero, brakes, mass/grip, tyres, slipstream), and reads/writes the legacy .m2d magic-data format plus a new, human-readable physics TOML format.

⚠️ BACK UP YOUR GP2.EXE FIRST

This tool patches GP2.EXE in place. Before you write anything, keep your own copy of the original executable somewhere safe.

As a safety net, the editor automatically copies the file to GP2.EXE.bak once (the first time you write), and verifies every write by reloading the file and comparing bytes. But the .bak is only created on the first write and is never overwritten — it is not a substitute for your own backup. If you patch a file you already patched before, the .bak still holds the previous state, not the factory original. Keep a pristine copy yourself.

System requirements

GP2 Workshop draws its interface with OpenGL (eframe's glow backend), so it needs a working OpenGL 2.1+ driver on the machine that runs it:

• On any PC with normal GPU drivers installed, this is already the case.
• On a bare Windows 7 install that only has Microsoft's default software OpenGL 1.1 (i.e. no GPU vendor driver), the window will fail to render. Install the GPU driver (Intel/NVIDIA/AMD) first.

Windows 7 also needs a dedicated build — Rust dropped Windows 7/8 support in 1.78, so the ordinary Windows build fails at launch with a missing api-ms-win-core-*.dll. See docs/WINDOWS7-BUILD.md for how the Win7 package is produced.

What it does

• Magic Data tab — pick a slot (1–16), edit the 24 tables in a labelled grid, and Import/Export the slot directly to/from the EXE or Load/Save a .m2d file. The .m2d format is unchanged from the old editor (24 decimal lines, table order 1–24, one file per slot), so files are interchangeable. Table 6 is dead data (ignored by the game) and is shown disabled.
• Physics tab — sub-tabs for Engine, Power Curve, Aero, Brakes, Mass/Grip, Tyres and Slipstream. Basic fields are always shown; Advanced fields live behind a collapsing section. Fixed-point fields show their float value and a hex tooltip, and every field has a "↺ stock" reset button. The Power Curve sub-tab has an editable 36-entry table plus a line plot. Import/Export the whole physics set to/from the EXE, or Load/Save it as TOML.

A calibration step verifies known stock values in the EXE before any write. If the file calibrates you'll see a green ✓ calibrated (Δ=0x…) badge; if it can't be calibrated (unknown/garbage image) the badge reads ⚠ uncalibrated and all Export-to-EXE actions are disabled (you can still load/save files).

Scope

In scope: the 24 magic-data tables, the curated physics inventory above, the power curve, the four tyre compounds' base grip/wear + worn floor. Out of scope in this version: deep editing of the tyre wear curve and track-abrasion tables (read-only / Advanced), per-car horsepower, track management, and saved-game editing.

Project layout

• crates/gp2ws-core — all logic (offsets, calibration, encoding, field registry, .m2d and TOML I/O). No GUI, fully unit-tested. The GUI holds no file offsets — it only talks to the Session façade.
• crates/gp2ws-gui — the eframe/egui desktop application.

Building

Native (Linux / macOS / Windows)

cargo build --release -p gp2ws-gui
cargo run -p gp2ws-gui

Cross-compiling to Windows from Linux

The Windows binary is built with the GNU toolchain via mingw-w64. One-time setup:

rustup target add x86_64-pc-windows-gnu
sudo apt-get install -y mingw-w64          # Debian/Ubuntu

.cargo/config.toml already points the linker at x86_64-w64-mingw32-gcc, so:

cargo build --release --target x86_64-pc-windows-gnu -p gp2ws-gui

produces target/x86_64-pc-windows-gnu/release/gp2ws-gui.exe.

Testing

cargo test

Some integration tests verify offsets/values against a real GP2.EXE. They are skipped unless you point them at a reference executable via the GP2WS_TEST_EXE environment variable (the EXE is never committed to this repo):

GP2WS_TEST_EXE=/path/to/GP2.EXE cargo test

Technical notes

• GP2.EXE is an uncompressed DOS executable; it is patched raw at file offsets. All multi-byte values are little-endian; fixed-point is Q.14 (0x4000 = 1.0).
• The standard EXE has no segment shift (Δ = 0). Calibration first tries Δ = 0, then a small window-scan fallback to derive a consistent delta.