While we're thrilled that there is so much interest in reverse engineering LEGO Island and are happy to accept contributions from anyone who would like to help progress us further to our goal of a complete codebase, proposed changes to this repository must adhere to a certain degree of engineering quality. While the established contributors here are more than happy to provide code reviews and constructive criticism, it is not their job to teach potential contributors C++ or decompilation fundamentals. As a project that is largely an artifact of the free time of its contributors, the more of that (often scarce) resource that can be dedicated to efficient work, the faster the decompilation will progress. Unfortunately, this results in well-intentioned but poorly constructed contributions actually hurting progress in the long-term. While we are greatly appreciative of the sentiment, if you aren't very confident in your decompilation abilities, it is generally in the project's best interest that you return when you have a better grasp over the process.
Generally, decompilation is a fairly advanced skill. Depending on your current proficiency with C/C++ and x86 assembly, it could take you months or even years to learn the skills necessary to do it adequately. If you're still interested in learning, [part 1 of the decompilation vlog](https://www.youtube.com/watch?v=MToTEqoVv3I) covers the overall process and should give you a starting point that you can dive in from. Once again, please make yourself familiar with this process before attempting to contribute code to this project.
For documenting the original binaries and generating pseudocode that we decompile with, we primarily use [Ghidra](https://ghidra-sre.org/) (it's free and open source). To help with collaboration, we have a shared Ghidra repository with all of our current work. You are free to check it out and mess around with it locally, however to prevent sabotage, you will need to request permission before you can push your changes back to the server (ask in the Matrix room).
**Please note that at the time of writing, much of the information found on the Ghidra server is severely outdated**. Generally, the source code found in this repository represents the latest "source of truth" and should be referenced whenever possible.
Please keep your pull requests small and understandable; you may be able to shoot ahead and make a lot of progress in a short amount of time, but this is a collaborative project, so you must allow others to catch up and follow along. Large pull requests become significantly more unwieldy to review, and as such make it exponentially more likely for a mistake or error to go undetected. They also make it harder to merge other pull requests because the more files you modify, the more likely it is for a merge conflict to occur. A general guideline is to keep submissions limited to one class at a time. Sometimes two or more classes may be too interlinked for this to be feasible, so this is not a hard rule, however if your PR is starting to modify more than 10 or so files, it's probably getting too big.
This repository currently has only one goal: accuracy to the original executables. We are byte/instruction matching as much as possible, which means the priority is making the original compiler (MSVC 4.20) produce code that matches the original game. As such, modernizations and bug fixes will probably be rejected for the time being.
* [`3rdparty`](/3rdparty): Contains code obtained from third parties, not including Mindscape. Generally, these are libraries that have been placed in the public domain or are freely available on the web. As these are unaltered files, our style guide (see below) does not apply.
* [`ISLE`](/ISLE): Decompilation of `ISLE.EXE`. It depends on some code in `LEGO1`.
* [`LEGO1`](/LEGO1): Decompilation of `LEGO1.DLL`. This folder contains code from Mindscape's custom in-house engine called **Omni** (file pattern: `mx*`), the LEGO Island-specific extensions for Omni and the game's code (file pattern: `lego*`) as well as several utility libraries developed by Mindscape.
* [`tools`](/tools): A set of tools aiding in the decompilation effort.
Please make yourself familiar with the [available tooling and annotations](/tools/README.md). These are generally required to contribute to the project.
## Notes on MSVC 4.20
As outlined in the [`README`](/README.md), Microsoft Visual C++ 4.20 is the compiler we use to build the game.
One important aspect to know about this compiler in the context of the decompilation project is that the assembly code generation is somewhat erratic. We call this peculiarity "compiler randomness" or entropy. In essence, what it comes down to is that changes to the code base, for instance in a header, can pseudo-randomly affect the code generation of functions in compilation units that include this header, even if the changes are completely unrelated to those functions. For example, by adding an extra (unused) inline function or an enum declaration in a header, the code in some functions may unexpectedly wind up looking different and our main tool, [`reccmp`](/tools/README.md), will report either a (significantly) reduced or increased accuracy for those functions. This issue roughly affects around ~5% of all decompiled functions.
We are currently unaware of the exact nature of this phenomenon. Unfortunately it represents a significant obstacle in our effort to achieve 100% matching binaries. If you or anyone you know has knowledge about the compiler internals that lead to the described observations, please contact us.
In general, we're not exhaustively strict about coding style, but there are some preferable guidelines to follow that have been adopted from what we know about the original codebase:
We are currently using [clang-format](https://clang.llvm.org/docs/ClangFormat.html) and [clang-tidy](https://clang.llvm.org/extra/clang-tidy/) with configuration files that aim to replicate the code formatting employed by the original developers. There are [integrations](https://clang.llvm.org/docs/ClangFormat.html#vim-integration) available for most editors and IDEs. The required `clang` toolchain version is `18.x`.
We are currently using a customized version of [ncc](https://github.com/nithinn/ncc) with a configuration file that aims to replicate the naming conventions employed by the original developers. `ncc` requires Clang `16.x`; please refer to the [tool](/tools/ncc) and the [GitHub action](/.github/workflows/naming.yml) for guidance.
For any further questions, feel free to ask in either the [Matrix chatroom](https://matrix.to/#/#isledecomp:matrix.org) or on the [forum](https://forum.mattkc.com/viewforum.php?f=1).
