Table of Contents

This repo has two main branches:

Branch	Description
accurate	The main decompilation branch. The code is 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.

CSE2 (Portable)

CSE2 is a decompilation of Cave Story.

This branch migrates the engine away from WinAPI and DirectX, and addresses numerous portability issues, allowing it to run on other platforms.

Supported platforms include...

• Windows
• Linux
• macOS
• Wii U
• 3DS
• RISC OS

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 Simon Parzer and Peter Mackay. Details about it can be found on Peter's old blog. This port received an update in 2011, including two shiny new executables. What they 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, 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 2005 sucks.

Dependencies

• SDL2 (if BACKEND_AUDIO or BACKEND_PLATFORM are set to SDL2)
• GLFW3 (if BACKEND_PLATFORM is set to GLFW3)
• FreeType (if FREETYPE_FONTS is enabled)

If these are not found, they will be built locally.

In addition, pkg-config is required for builds that require static-linkage.

A list of dependencies for specific platforms can be found on the wiki.

Building

This project uses CMake, allowing it to be built with a range of compilers.

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 should append -G"MSYS Makefiles" -DPKG_CONFIG_STATIC_LIBS=ON 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 ability to drag-and-drop save files onto the window
-DDOCONFIG=OFF	Disable compiling the DoConfig tool (it is not useful for console ports)
-DDOCONFIG_LEGACY_OPENGL=ON	Make DoConfig use OpenGL 2.1 instead of OpenGL 3.2 (useful for older/limited platforms)
-DLANCZOS_RESAMPLER=ON	Use Lanczos filtering for audio resampling instead of linear-interpolation (Lanczos is more performance-intensive, but higher quality)
-DFREETYPE_FONTS=ON	Use FreeType2 to render the DejaVu Mono (English) or Migu1M (Japanese) fonts, instead of using pre-rendered copies of Courier New (English) and MS Gothic (Japanese)
-DBACKEND_RENDERER=OpenGL3	Render with OpenGL 3.2 (hardware-accelerated)
-DBACKEND_RENDERER=OpenGLES2	Render with OpenGL ES 2.0 (hardware-accelerated)
-DBACKEND_RENDERER=SDLTexture	(Default) Render with SDL2's Texture API (hardware-accelerated) (note: requires -DBACKEND_PLATFORM=SDL2)
-DBACKEND_RENDERER=SDLSurface	Render with SDL2's Surface API (software-rendered) (note: requires -DBACKEND_PLATFORM=SDL2)
-DBACKEND_RENDERER=WiiU	Render with the Wii U's GX2 API (hardware-accelerated)
-DBACKEND_RENDERER=3DS	Render with the 3DS's Citro2D/Citro3D API (hardware-accelerated)
-DBACKEND_RENDERER=Software	Render with a handwritten software-renderer
-DBACKEND_AUDIO=SDL2	(Default) Deliver audio with SDL2 (software-mixer)
-DBACKEND_AUDIO=miniaudio	Deliver audio with miniaudio (software-mixer)
-DBACKEND_AUDIO=WiiU-Hardware	Deliver audio with Wii U's AXVoice API (hardware-accelerated) (WARNING - currently broken: voices randomly disappear for unknown reasons)
-DBACKEND_AUDIO=WiiU-Software	Deliver audio with Wii U's AXVoice API (software-mixer)
-DBACKEND_AUDIO=3DS-Hardware	Deliver audio with 3DS's NDSP API (hardware-accelerated)
-DBACKEND_AUDIO=3DS-Software	Deliver audio with 3DS's NDSP API (software-mixer)
-DBACKEND_AUDIO=Null	Don't deliver audio at all (WARNING - game will have no audio)
-DBACKEND_PLATFORM=SDL2	(Default) Use SDL2 for miscellaneous platform-dependant operations
-DBACKEND_PLATFORM=GLFW3	Use GLFW3 for miscellaneous platform-dependant operations
-DBACKEND_PLATFORM=WiiU	Use the Wii U's native APIs for miscellaneous platform-dependant operations
-DBACKEND_PLATFORM=3DS	Use the 3DS's native APIs for miscellaneous platform-dependant operations
-DBACKEND_PLATFORM=Null	Don't do platform-dependant operations at all (WARNING - game will have no video or input)
-DLTO=ON	Enable link-time optimisation
-DPKG_CONFIG_STATIC_LIBS=ON	On platforms with pkg-config, static-link the dependencies (good for Windows builds, so you don't need to bundle DLL files)
-DMSVC_LINK_STATIC_RUNTIME=ON	Link the static MSVC runtime library, to reduce the number of required DLL files (Visual Studio only)
-DFORCE_LOCAL_LIBS=ON	Compile the built-in versions of SDL2, GLFW3, and FreeType instead of using the system-provided ones

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 executables can be found in the game_english/game_japanese folder, depending on the selected language.

Building for the Wii U

To target the Wii U, you'll need devkitPro, devkitPPC, and WUT.

First, add the devkitPPC tools directory to your PATH (because WUT's CMake support is broken, as of writing):

PATH=$PATH:$DEVKITPPC/bin

Then, generate the build files with this command:

cmake -B buildwiiu -DCMAKE_BUILD_TYPE=Release -DFORCE_LOCAL_LIBS=ON -DBACKEND_PLATFORM=WiiU -DBACKEND_RENDERER=WiiU -DBACKEND_AUDIO=WiiU-Software -DDOCONFIG=OFF -DCMAKE_TOOLCHAIN_FILE=$DEVKITPRO/wut/share/wut.toolchain.cmake

Finally, build the game with this command:

cmake --build buildwiiu

This will build a binary, but you still need to convert it to an .rpx file that can be ran on your Wii U.

First, we need to strip the binary:

powerpc-eabi-strip -g game_english/CSE2

Then, we convert it to an .rpx:

elf2rpl game_english/CSE2 game_english/CSE2.rpx

game_english/CSE2.rpx is now ready to be ran on your Wii U. This port expects the data folder to be in a folder called CSE2-portable-en/CSE2-portable-jp on the root of your SD card.

Building for the 3DS

To target the 3DS, you'll need devkitPro, devkitARM, Citro2D, Citro3D, libctru, and bannertool, along with the 3dstools and devkitpro-pkgbuild-helpers packages.

Open a terminal, and cd into the CSE2 directory. Then execute this command:

cmake -B build3ds -DCMAKE_BUILD_TYPE=Release -DFORCE_LOCAL_LIBS=ON -DBACKEND_PLATFORM=3DS -DBACKEND_RENDERER=3DS -DBACKEND_AUDIO=3DS-Hardware -DDOCONFIG=OFF -DFREETYPE_FONTS=ON -DCMAKE_TOOLCHAIN_FILE=$DEVKITPRO/cmake/3DS.cmake -DCTRU_ROOT=$DEVKITPRO/libctru

(Note that FREETYPE_FONTS is enabled. If you're creating a Japanese build, it's best to disable this, as the FreeType font is unreadable at 320x240).

This will create the build files. To build CSE2, run:

cmake --build build3ds

This will create an elf file. Before we can create a .3dsx file from it, we need to make an .smdh file:

bannertool makesmdh -i $DEVKITPRO/libctru/default_icon.png -s "CSE2" -l "Port of Cave Story" -p "Clownacy" -o build3ds/smdh.smdh

We can finally generate a .3dsx file:

3dsxtool game_english/CSE2.elf game_english/CSE2.3dsx --romfs=game_english/data --smdh=build3ds/smdh.smdh

Licensing

Being a decompilation, the majority of the code in this project is proprietary and belongs to Daisuke "Pixel" Amaya.

Modifications and custom code are made available under the MIT licence. See LICENCE.txt for details.