snuri00 / ps2-web-recomp

# PS2 Web Recomp
PlayStation 2 games running in the browser through static recompilation. The game's Emotion Engine machine code is translated ahead of time into C++ and compiled to WebAssembly, so the main CPU is never interpreted; the rest of the console, its operating system and hardware, is emulated by a runtime that draws with WebGPU.
 Watch the full recording (1:24) 
This is the sibling of psp-web-recomp and follows the same method. The first title brought up this way is Gran Turismo 4, chosen because it is one of the most demanding games on the system: it leans on both vector units, on exact floating point behaviour for its replays and license tests, and on graphics tricks that read rendered images back as palettes. It plays from boot through the opening movie, the menus and races, with music and sound effects, and saves to a memory card kept in the browser. A race runs at full speed, 50 frames per second for this PAL release, in Chrome on a laptop's integrated GPU at twice the PS2's resolution, which is how the recording above was made.
God of War II followed through the same scripts. It needed no game-specific code, but it found two bugs that Gran Turismo 4 had never triggered, one in the recompiler and one in the vector unit timing, and a few missing pieces of the PS2's input/output processor. It now plays from the menus through its cutscenes into combat, and holds 60 frames per second in heavy combat at the PS2's resolution in Chrome. At twice the resolution it runs at 48 to 60, limited by the laptop's integrated GPU.
No game data is included here. You bring a disc image of a game you own, and the scripts in this repository turn it into a web page on your machine.
## How it works
**Recompilation.** `eerecomp` reads the game's executable, follows its control flow to find the functions and emits C++ for them in units of 16 KiB of guest code. The output keeps the R5900's quirks: 128-bit registers and the multimedia instructions that work on them, branch delay slots, the PS2's floating point unit, which has no infinities or denormals and rounds differently from IEEE, and vector unit 0 used as a coprocessor. Jumps between units become tail calls, and a thread switch unwinds the host stack and resumes at the guest address, so the generated code never needs a stack per guest thread.
**A small PS2 kernel.** The EE side of the operating system is answered by high-level emulation: threads, semaphores, interrupt handlers for the DMA controller and the vertical blank, alarms, and the SIF channel that connects the main CPU to the I/O processor. The I/O processor runs the game's own IRX modules, the sound driver, the disc streaming code and the controller and memory card drivers that ship on the disc, on an interpreter of its R3000 CPU, while the IOP kernel and the libraries those modules call are reimplemented in C++. The disc is read over HTTP Range requests, so only the executable is downloaded up front.
**Vector units.** Most of a PS2 game's 3D