LEGO Island Decompilation

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This is a complete decompilation of LEGO Island (Version 1.1, English). It aims to be as accurate as possible, matching the recompiled instructions to the original machine code as much as possible. The goal is to provide a workable codebase that can be modified, improved, and ported to other platforms later on.

Note: This repository is for decompilation only and its code is true to the original release. It will not compile for targets other than 32-bit Windows. For a modern adaptation of the LEGO Island codebase with native compatibility for all major platforms and the Web, see isle-portable instead.

Status

The reccmp reports compare every recompiled function with the retail binary. The ReproBit report records the cold rebuild that reproduced all three binaries byte for byte and links its full report.json record; both are regenerated by every verified push to master.

CONFIG.EXE, ISLE.EXE, and LEGO1.DLL are completely decompiled. The project's reviewed ReproBit build uses the original Microsoft Visual C++ 4.2 toolchain and reproduces all three retail binaries byte for byte. Work continues on naming, documentation, and source clarity without changing those results.

Building

There are two build paths:

• ReproBit produces and certifies the exact release binaries.
• The ordinary CMake build is useful for day-to-day development, but its outputs are not release-certified.

Reproduce the retail binaries exactly

Start with a fresh checkout and install Python 3.11 or newer, Git, and ReproBit. macOS and Linux also need Wine. Place your English 1.1 retail files at legobin/CONFIG.EXE, legobin/ISLE.EXE, and legobin/LEGO1.DLL, then run these commands from the repository root:

rbit setup .
rbit verify .

setup obtains and checks the original compiler. verify builds everything from scratch and checks every byte against the retail files. A successful run writes build/CONFIG.EXE, build/ISLE.EXE, and build/LEGO1.DLL; open .reprobit-state/reports/report.html to review the result. Use rbit build . for faster incremental builds while editing, then run rbit verify . before sharing a result.

GitHub Actions uses the same verification for the continuous release, which includes the exact binaries, reccmp progress files, and ReproBit's readable report.html plus its full report.json record; the reports are also published to the progress pages linked under Status. Every run compares its reccmp scores and its ReproBit intervention cost with the master release and prints the deltas in the job log. The ordinary CMake instructions below remain useful for development builds, but only ReproBit certifies byte-for-byte release outputs.

Ordinary developer build

This project uses the CMake build system with several compilers and development environments. Microsoft Visual C++ 4.20 is the original game's compiler and remains the most representative choice. ReproBit's byte-for-byte verification is the authoritative result for contributions and releases.

These instructions build useful local binaries with Visual C++ 4.2. They do not replace ReproBit's exact verification. Other compilers may work for experimentation, but are not covered here.

Prerequisites

You will need the following software installed:

• Microsoft Visual C++ 4.2. This can be found on many abandonware sites, but the installer can be a little iffy on modern versions of Windows. For convenience, a portable version is available that can be downloaded and used quickly instead.
• CMake. A copy is often included with the "Desktop development with C++" workload in newer versions of Visual Studio; however, it can also be installed as a standalone app.

Compiling

1. Open a Command Prompt (cmd).
2. From Visual C++ 4.2, run BIN/VCVARS32.BAT x86 to populate the path and other environment variables for compiling with MSVC.
3. Make a folder for compiled objects to go, such as a build folder inside the source repository (the folder you cloned/downloaded to).
4. In your Command Prompt, cd to the build folder.
5. Configure the project with CMake by running:

cmake <path-to-source> -G "NMake Makefiles" -DCMAKE_BUILD_TYPE=RelWithDebInfo

• Visual C++ 4.2 has issues with paths containing spaces. If you get configure or build errors, make sure neither CMake, the repository, nor Visual C++ 4.2 is in a path that contains spaces.
• Be aware that long file paths (e.g., C:\Users\LongUserName\LongerFolderName\isle) may be truncated by make, resulting in “File not found” errors.
• Replace <path-to-source> with the source repository. This can be .. if your build folder is inside the source repository.
• RelWithDebInfo is recommended because it will produce debug symbols useful for further decompilation work. However, you can change this to Release if you don't need them. While Debug builds can be compiled and used, they are not recommended as the primary goal is to match the code to the original binary. This is because the retail binaries were compiled as Release builds.
• NMake Makefiles is most recommended because it will be immediately compatible with Visual C++ 4.2. For faster builds, you can use Ninja (if you have it installed), however due to limitations in Visual C++ 4.2, you can only build Release builds this way (debug symbols cannot be generated with Ninja).

1. Build the project by running nmake or cmake --build <build-folder>
2. When this is done, there should be recompiled CONFIG.EXE, ISLE.EXE, and LEGO1.DLL files in the build folder.
3. Note that nmake must be run twice under certain conditions, so it is advisable to always (re-)compile using nmake && nmake.

If you have a CMake-compatible IDE, it should be pretty straightforward to use this repository, as long as you can use VCVARS32.BAT and set the generator to NMake Makefiles.

Docker

Alternatively, we support Docker as a method of compilation. This is ideal for users on Linux and macOS who do not wish to manually configure a Wine environment for compiling this project.

Compilation should be as simple as configuring and running the following command:

docker run -d \
	-e CMAKE_FLAGS="-DCMAKE_BUILD_TYPE=RelWithDebInfo" \
	-v <path-to-source>:/isle:rw \
	-v <build-folder>:/build:rw \
	ghcr.io/isledecomp/isle:latest

<path-to-source> should be replaced with the path to the source code directory (ie: the root of this repository). <build-folder> should be replaced with the path to the build folder you'd like CMake to use during compilation.

You can pass as many CMake flags as you'd like in the CMAKE_FLAGS environment variable, but the default configuration provided in the command is already ideal for building highly-accurate binaries.

Usage

The simplest way to use the recompiled binaries is to swap the original executables (ISLE.EXE, LEGO1.DLL, and CONFIG.EXE) in LEGO Island's installation directory for the ones that you've built from this source code. By default, LEGO Island is installed to C:\Program Files\LEGO Island on 32-bit operating systems and C:\Program Files (x86)\LEGO Island on 64-bit operating systems.

For advanced users, you can get LEGO Island to run from anywhere as long as ISLE.EXE and LEGO1.DLL are in the same directory and the cdpath and diskpath registry keys (usually found in HKEY_LOCAL_MACHINE\Software\Mindscape\LEGO Island on 32-bit operating systems and HKEY_LOCAL_MACHINE\Software\Wow6432Node\Mindscape\LEGO Island on 64-bit operating systems) point to the correct location for the asset files (the directory that contains the LEGO folder).

If you see an error about d3drm.dll, you will need to acquire a copy and place it in the same directory as the game executables, as it has not shipped with Windows since Windows XP. We have published a known good copy here that works with LEGO Island.

Contributing

If you're interested in helping or contributing to this project, check out the CONTRIBUTING page.

Additional Information

Which version of LEGO Island do I have?

Right click on LEGO1.DLL, select Properties, and switch to the Details tab. Under Version you should either see 1.0.0.0 (1.0) or 1.1.0.0 (1.1). Additionally, you can look at the game disc files; 1.0's files will all say August 8, 1997, and 1.1's files will all say September 8, 1997. Version 1.1 is by far the most common, especially if you're not using the English or Japanese versions, so that's most likely the version you have.

Please note that some localized versions of LEGO Island were recompiled with small changes despite maintaining a version number parallel with other versions; this decompilation specifically targets the English release of version 1.1 of LEGO Island. You can verify you have the correct version using the checksums below:

• ISLE.EXE md5: f6da12249e03eed1c74810cd23beb9f5
• LEGO1.DLL md5: 4e2f6d969ea2ef8655ba3fc221a0c8fe
• CONFIG.EXE md5: 92d958a64a273662c591c88b09100f4a