Forza Motorsport (Xbox) — static recompilation

A native build of Microsoft Game Studios' Forza Motorsport (Xbox, 2005; title ID 0x4D53006E) made with the DirectXbox-Recomp toolkit. The game's own code is lifted to C from the XBE and runs natively; Direct3D 8 and DirectSound are replaced at the API boundary.

No game code or data is in this repository. You need the files from a copy of the disc you own.

Current State

Early bring-up. On macOS (Apple Silicon) it boots, fills its cache partitions from the disc, plays the intro movie with its music, creates a profile, and goes through the main menu and car select into a race, with the track, cars and HUD drawn. The front end runs at 60 fps; a race costs about 18 ms a frame on an M-series Mac, so it runs a little under 60.

Forza does its profile and save work on an XAPI fiber. The toolkit replaces SwitchToFiber with host fibers (src/hle/hle_xapi_fiber.c); a toolkit without that on your platform stops presenting frames after "New profile".

• Widescreen (widescreen = 1, launcher or RECOMP_WIDESCREEN=1). Forza has a 16:9 mode of its own: races fill the 16:9 picture with a wider view and the HUD sits at the 16:9 edges, as the game shipped it. Every frame is 16:9. Movies are shown in proportion between bars. The menus are laid out for 16:9 as they load: the frame (bands, headings, button prompts) runs to the edges, and the background art is widened from your own disc, its stripes carried on rather than stretched (layout/widescreen.txt, src/fz_layout.c, src/fz_backdrop.c), the track loading pictures included. The content of each menu still sits in the 4:3 middle; moving it into the wider space, screen by screen, is next.

Not yet checked: a race to the finish, the other modes, saving and loading, and the sound by ear.

Layout

forza-recomp/
  CMakeLists.txt          the project; pulls in ../xboxrecomp
  src/main.c              entry point, game folder lookup (from the toolkit's template)
  src/recomp_manual.c     the title's own overrides and hooks (pool, widescreen)
  src/fz_layout.c         menu layouts for 16:9: rules applied as each screen loads
  src/fz_backdrop.c       menu backgrounds widened for 16:9 when the game loads them
  layout/widescreen.txt   the 16:9 layout rules and background recipes
  src/recomp/gen/         lifted code (generated, not committed)
  scripts/recompile.sh    runs the toolkit's lift pipeline for this game
  game/                   your game files (not committed)

recomp_manual.c replaces the two functions that take and give back a page of Forza's small-object pool, so that every pool page keeps a 64 KB window to itself. operator delete tells pool slots from heap blocks by one bit per 64 KB region, which holds on the console and not here; without the overrides the heap is corrupt by the first race load. The comment above them has the details.

Building

You need the toolkit checked out beside this repository, at ../xboxrecomp, at a commit with the fixes this game needs. Until they are on the toolkit's main, that is its title/forza branch. Point XBOXRECOMP_DIR elsewhere to use another checkout, both for scripts/recompile.sh and for CMake (-DXBOXRECOMP_DIR=...).

The toolkit's own requirements apply: see its docs/GETTING_STARTED.md.

1. Game files. Extract the disc into game/, so that game/default.xbe exists.

2. XDK symbols. From the toolkit (it builds the XbSymbolDatabase CLI in third_party/XbSymbolDatabase/build):

   .venv/bin/python -m tools.xdk_symbols ../forza-recomp/game/default.xbe

3. Lift. scripts/recompile.sh (about a minute; 20,585 functions).

4. Build.

   cmake -S . -B build/Release -G Ninja -DCMAKE_BUILD_TYPE=Release
   cmake --build build/Release --target forza_recomp forza_launcher --parallel

Running

build/Release/forza_launcher      # settings, then the game
build/Release/forza_recomp        # the game directly

The first boot copies the game's archives to the cache partitions, which takes a minute or two before the intro movie starts. F9 shows the frame rate, F10 steps the frame cap, F11 saves a capture of the frame on screen.