Table of Contents

This repo has multiple branches:

Branch	Description
accurate	The main decompilation branch. The code intended to be as close to the original as possible, down to all the bugs and platform-dependencies.
portable	This branch ports the engine away from WinAPI and DirectX, and addresses numerous portability issues, allowing it to run on other platforms.
enhanced	Based on the portable branch, this adds several enhancements to the engine, and makes it more accessible to modders.
emscripten	Modifies the engine to build with Emscripten, allowing it to run in web browsers (no longer maintained).
wii	Ports the engine to the Nintendo Wii (no longer maintained).

Cave Story Engine 2

Cave Story Engine 2 is a decompilation of Cave Story.

Background

When Pixel made Cave Story, he compiled the original Windows EXE with no optimisations. This left the generated assembly code extremely verbose and easy to read. It also made the code very decompiler-friendly, since the assembly could be mapped directly back to the original C(++) code.

Technically, this alone made a decompilation feasible, as was the case for the Super Mario 64 decompilation project - however, there was more to be found...

In 2007, a Linux port of Cave Story was made by Peter Mackay and Simon Parzer. Details about it can be found on Peter's old blog. This port received an update in 2011, including two shiny new executables. What Peter and Simon didn't realise was that they left huge amounts of debugging information in these executables, including the names of every C++ source file, as well as the variables, functions, and structs they contained.

This was a goldmine of information about not just the game's inner-workings, but its source code. This is the same lucky-break the Diablo decompilation project had. With it, much of the game's code was pre-documented and explained for us, saving us the effort of doing it ourselves. In fact, the combination of easy-to-decompile code, and a near-full set of function/variable names, reduced much of the decompilation process to mere copy-paste.

To top it all off, some of Cave Story's original source code would eventually see the light of day...

In early 2018, the Organya music engine was released on GitHub by an old friend of Pixel's. On top of providing an insight into Pixel's coding style, this helped with figuring out one of the most complex parts of Cave Story's codebase.

And... that's it! It's not often that a game this decompilable comes along, so I'm glad that Cave Story was one of them. Patching a dusty old executable from 2004 has its downsides.

Building

Visual Studio .NET 2003

Project files for Visual Studio .NET 2003 are available, and can be found in the 'vs2003' folder.

As proven by the original Doukutsu.exe's Rich Header, Pixel used Visual Studio .NET 2003 to compile Cave Story. This means these project files allow us to check the accuracy of the decompilation by comparing the generated assembly code to that of the original executable. The tool for this can be found in the 'devilution' folder.

CMake (Visual Studio & MinGW-w64)

Switch to the terminal (Visual Studio users should open the Developer Command Prompt) and cd into this folder. After that, generate the files for your build system with:

cmake -B build -DCMAKE_BUILD_TYPE=Release

MSYS2 users may want to append -G"MSYS Makefiles" to this command, also.

You can also add the following flags:

Name	Function
-DJAPANESE=ON	Enable the Japanese-language build (instead of the unofficial Aeon Genesis English translation)
-DFIX_BUGS=ON	Fix various bugs in the game
-DDEBUG_SAVE=ON	Re-enable the dummied-out 'Debug Save' option, and the ability to drag-and-drop save files onto the window
-DLTO=ON	Enable link-time optimisation
-DMSVC_LINK_STATIC_RUNTIME=ON	Link the static MSVC runtime library, to reduce the number of required DLL files (Visual Studio only)

You can pass your own compiler flags with -DCMAKE_C_FLAGS and -DCMAKE_CXX_FLAGS.

You can then compile CSE2 with this command:

cmake --build build --config Release

If you're a Visual Studio user, you can open the generated CSE2.sln file instead, which can be found in the build folder.

Once built, the executable can be found in the game_english/game_japanese folder, depending on the selected language.

Makefile (MinGW-w64) [deprecated - use CMake instead]

Run 'make' in this folder, preferably with some of the following settings:

Name	Function
JAPANESE=1	Enable the Japanese-language build (instead of the unofficial Aeon Genesis English translation)
FIX_BUGS=1	Fix various bugs in the game
DEBUG_SAVE=1	Re-enable the dummied-out 'Debug Save' option, and the ability to drag-and-drop save files onto the window
RELEASE=1	Compile a release build (optimised, stripped, etc.)
STATIC=1	Produce a statically-linked executable (so you don't need to bundle DLL files)

You can pass your own compiler flags by defining CXXFLAGS.

Once built, the executable can be found in the game_english/game_japanese folder, depending on the selected language.

Licensing

Being a decompilation, the majority of the code in this project belongs to Daisuke "Pixel" Amaya - not us. We've yet to agree on a licence for our own code.