ReC98/CONTRIBUTING.md

Welcome!

If we've seen you doing any kind of reverse-engineering or modding work on the PC-98 Touhou games before, you might have already been invited as a collaborator. In that case, feel free to create separate branches for your work directly in this repository – this will immediately inform anyone who watches this repo or subscribed to a webhook. If you prefer, you can still use your own fork though.

What can I do on these separate branches?

Anything – reverse-engineering and decompilation of original ZUN code (which then could be merged back into master after review) or your own custom mods, no matter how large or small.

For starters, simply naming functions or global variables to reflect their actual intent will already be helpful. Any name is better than sub_<something>, and can always be fixed or improved later.

Contribution guidelines

Rule #1

master must never introduce code changes that change the decompressed program image, or the unordered set of relocations, of any original game binary, as compared using mzdiff. The only allowed exceptions are:

1. different encodings of identical x86 instructions within code segments
2. padding with 00 bytes at the end of the file.

Taste issues

• Use tabs for indentation.

• Spaces for alignment are allowed, especially if they end up giving the code a nice visual structure, e.g. with multiple calls to the same function with varying pixel coordinates.

• Don't indent extern "C" blocks that span the entire file.

• Always use { brackets }, even around single-statement conditional branches.

• Add spaces around binary operators. for(i = 0; i < 12; i++)

• Variables should be signed in the absence of any ASM instruction (conditional jump, arithmetic, etc.) or further context (e.g. parameters with a common source) that defines their signedness. If a variable is used in both signed and unsigned contexts, declare it as the more common one.

Code organization

• Try to avoid repeating numeric constants – after all, easy moddability should be one of the goals of this project. For local arrays, use sizeof() if the size can be expressed in terms of another array or type. Otherwise, #define a macro if there is a clear intent behind a number. (Counterexample: Small, insignificant amounts of pixels in e.g. entity movement code.)

• Documenting function comments exclusively go into C/C++ header files, right above the corresponding function prototype, not into ASM slices.

• Newly found function prototypes, structs, and "sequence of numeric equate" enums defined in ASM land should immediately be reflected in a header file in C/C++ land, with the correct types and calling conventions.

• Try moving repeated sections of code into a separate inline function before grabbing the #define hammer. Turbo C++ will generally inline everything declared as inline that doesn't contain do, for, while, goto, switch, break, continue, or case.

• These inlining rules also apply to C++ class methods, so feel free to declare classes if you keep thinking "overloaded operators would be nice here" or "this code would read really nicely if this functionality was encapsulated in a method". (Sometimes, you will have little choice, in fact!) Despite Turbo C++'s notoriously outdated C++ implementation, there are quite a lot of possibilites for abstractions that inline perfectly. Subpixels, as seen in 9d121c7, are the prime example here. Don't overdo it, though – use classes where they meaningfully enhance the original procedural code, not to replace it with an overly nested, "enterprise-y" class hierarchy.

Decompilation

• Don't try to decompile self-modifying code. Yes, it may be possible by calculating addresses relative to the start of the function, but as soon as someone starts modding or porting that function, things will crash at runtime. Inline ASM in C/C++ source files is fine, that will trip up future port developers at compile time. Self-modifying code can only do the same if it's kept in separate ASM files.

Naming conventions

• ASM file extensions: .asm if they emit code, .inc if they don't
• Macros defining the number of instances of an entity: <ENTITY>_COUNT
• Functionally identical reimplementations or micro-optimizations of master.lib functions: z_<master.lib function name>