While LEGO themed video games have become something of a staple, in 1997 they were something of an odity. LEGO Island became the first LEGO video game released outside of Japan in 1997 and become something of a hit with over one million copies sold. The game was beloved among fans and set the stage for more LEGO video games to come. In an effort of love, [MattKC] put together a team to reverse engineer the game.

The team set out with the intent to create a near perfect recreation of the codebase, relying on custom made tools to run byte checks on the rewrite compilation and the original binary. While the project is functionally complete, [MattKC] believes it is impossible to get a byte accurate codebase. This is because of what the team called “compiler entropy.” Strange behaviors exists inside of Microsoft’s Visual C++ compiler of the era, and small changes in the code have seemingly random effects to unrelated parts of the binary. To mitigate this issue would likely require either partially reverse engineering Visual C++ or brute forcing the code, both of which would take a large amount of effort and time for no real benefit.

Another interesting step the team had to work out was how the game handled graphics. In the version of Direct X used, the developers could chose between immediate mode and retained mode. The difference largely boils down to how models and assets are handled. In immediate mode, Direct X is largely just a render engine and everything else is handled by the developer. With retained mode, Direct X works more similarly to a game engine where all the model and asset management is handled by Direct X. Almost all developers ended up using immediate mode to the point that Microsoft deprecated support for retained mode. For this reason, if you were to download and run LEGO island on a modern Windows PC, it would yell at you for not having the proper libraries. There is debate about how best to handle this moving forward. The team could rely on an unsupported library from Microsoft, reverse engineer that library only making the functions needed, or using leaked source code.

With the completion of the reverse engineering, engineering can commence. For example, an annoying and persistent bug caused the game to crash if you tried to exit. While it was effective in closing the game, it also caused progress to be lost. That particular bug was fixed simply by initializing a variable in the game’s fronted. Interestingly, that bug was not present in the late betas of the game that had been dug up from the depths of the internet leading to questions as to why a rewrite of the fronted was necessary so late in the development. Now efforts are commencing to port the game to other platforms which bring with it fresh headaches including rewriting for OpenGL and the balance of keeping a historically accurate game with the needs of modern development.