Spyro the Dragon Decompilation Project

[!WARNING] This project barely even started, while you can make some simple mods, the project evolving will probably throw a wrench into any mods you might actively be working on.

This project aims to decompile Spyro the Dragon to source code that will create a matching game executable. By achieving a byte-for-byte match, we can preserve the game and gain insights into its development.

I started this project late last year, I've been working on it on and off. Now that I've broken the 40% complete mark, I think it's time to make it public.

Structure

• src/: Decompiled source code.
• include/: Include headers for source code, and headers used by disassembly tools.
• assets/: Contains binary assets included in the executable.
• asm/: Disassembly for non-matching code, and code originally written in assembly.
• tools/: Contains utilities for building the game.

Target checksums

• PSX.EXE: 84E3728AB94720D0873E2514ADF4AADE4935E0C5 (SHA-1)
• PSX.EXE: A533D75CAB8AFAAE6107EC35A02A9A5FE979A92C7C955F9CF1EE50F693A1B998 (SHA-256)

Progress

Overlays

The way overlays were implemented in the Spyro trilogy is quite interesting, but were very challenging to match.

All level overlays have since been matched, but require a lot of documentation still. There's 2 functions left unmatched in the credits overlay.

They're made from the same set of files, but with bits and pieces included or excluded depending on the level. Which files are included in overlays is listed in overlays/overlays.yaml, and the classes included in levels are specified in overlays/mobys.yaml and overlays/particles.yaml. The source files used for producing the overlays are in the src/overlays/ directory.

PSYQ

Because I had trouble getting the order of the PSYQ sections to match, PSYQ 4.0 libraries are included in its disassembled form. If you prefer the more modern PSYQ 4.7, it's possible to replace it, creating a non-matching build. To build with PSYQ 4.7, use NEW_PSYQ=1 make all.

Please put PYSQ headers in psyq/include, if you're using 4.7 you should put the lib folder in psyq/lib. Any version of PSYQ later than 4.0 should work.

Building

To make it easier to setup the MIPS toolchain, a docker image is provided. Executing docker_env.sh starts a container in interactive mode with the Dockerfile image, which comes with modern mipsel- gcc and binutils. For the source code, a much older compiler will be used, gcc2.7.2-mipsel.

After starting the container, executing make all will create the main executable, named PSX.EXE, in the /build folder, and overlays in /build/wad.

To speed up the build process, you can use make -j followed by the number of threads you want to use, such as make all -j6.

The overlays will be output to /build/wad, the naming convention matches the Spyro 1 template of wadtool.

This project only concerns the game's code, not the data files.

A tool such as wadtool is needed to rebuild the WAD.WAD file, you can use it for extracting and rebuilding. For creating the CD image, I would recommend mkpsxiso because it's modern and capable of recreating the image perfectly. You can use dumpsxiso to extract the contents of the original image.

Acknowledgements

• splat and it's various example projects.
• spimdisasm disassembler used by splat
• maspsx
• decomp.me, a very handy tool for matching functions.

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Note: This project is a fan effort and is not affiliated with or endorsed by Sony Interactive Entertainment or Insomniac Games.

You got the shemp