melonDS/CONTRIBUTING.md

Contributor guide for melonDS

Please follow a style as documented here. Note that this guide was not always enforced, so some parts of the code violate it.

Files should use 4 spaces for indentation.

// for single line comments prefer C++ style

/*
    for multiline comments
    both C style comments
*/
// as well as
// C++ style comments are possible

// when including headers from the C standard library use their C names (so don't use cstdio/cstring, ...)
#include <stdio.h>

// namespaces in PascalCase
namespace Component
{ // for all constructs curly braces go onto the following line

// the content of namespaces should not be indented

int GlobalVariable; // in PascalCase

// function names should use PascalCase, parameters camelCase:
void Test(int someParam)
{
    int variable = someParam * 2; // local variables in camelCase
    
    // you can slightly vary the spacing around operators:
    int variable2 = someParam*2 + 1;
    // but avoid something like this: someParam* 2+ 3

    for (int i = 0; i < variable; i++) // always a space between if/for/while and the braces
    {
        // not using curly braces is allowed
        // if the body of the if/for/while is simple:
        if ((i % 2) == 0)
            printf("%d\n", i); // no space between the function name and the braces
    }
}

// defines should always be in CAPITALISED_SNAKE_CASE
#ifdef SOME_CONFIGURATION

// the content of #ifdef sections should not be indented
// the only exception being otherwise hard to read nested sections of #ifdef/#if/#defines
// as e.g. in ARMJIT_Memory.cpp

// prefer #ifdef/#ifndef, only use if defined(...) for complex expressions like this:
#if defined(THIS) || defined(THAT)
// ...
#endif

class MyClass // PascalCase
{
public: // access specfications are not indented
    void Test(int param) // for methods the same rules apply as for functions
    {
    }

private:
    int MemberVariable; // PascalCase, no prefix
};

#endif

#endif

enum
{
    // enums should always have a common prefix in camelCase
    // separated by an underscore with the item name
    // which has to be in PascalCase
    enumPrefix_FirstElement,
    enumPrefix_SecondElement,
    enumPrefix_ThirdElement,
    enumPrefix_FourthElement,
};

}

Some additional notes:

• Keep the definition and initialisation of local variables in one place and keep the scope of local variables as small as possible.

That means avoid code like this:

void ColorConvert(u32* dst, u16* vram)
{
    u16 color;
    u8 r, g, b;
    int i;

    for (i = 0; i < 256; i++)
    {
        color = vram[i];
        r = (color & 0x001F) << 1;
        g = (color & 0x03E0) >> 4;
        b = (color & 0x7C00) >> 9;

        dst[i] = r | (g << 8) | (b << 16);
    }
}

Do this instead:

void ColorConvert(u32* dst, u16* vram)
{
    for (int i = 0; i < 256; i++)
    {
        u16 color = vram[i];
        u8 r = (color & 0x001F) << 1;
        u8 g = (color & 0x03E0) >> 4;
        u8 b = (color & 0x7C00) >> 9;

        dst[i] = r | (g << 8) | (b << 16);
    }
}

• For integer types preferably use the explictly typed ones. We have short aliases for them defined in types.h (for unsigned types: u8, u16, u32, u16. For signed s8, s16, s32, s64). In some situations like loop variables, using int is possible as well.

• Don't overdo object oriented programming. Always try to use a simpler construct first, only use a polymorphic class if a namespace with functions in it doesn't cut it.

• In doubt put a namespace around your part of the code.

• C style strings (and the associated functions from the C standard library) are used in most places. We are thinking about changing this, as C strings are a bit of a hassle to deal with, but for the time being this is what we use.

• Only the C standard IO is used (so use printf, fopen, … Do not use std::cout/std::ostream, …).

• Complex C++ containers can be used (std::vector, std::list, std::map, …). std::array is usually not used, unless necessary so that the container can be used with other C++ constructs (e.g. <algorithm>). Only use them if a C array doesn't cut it.

• File names should be in PascalCase

• If a header file is called MyHeader.h it should be guarded with an ifdef like this:

#ifndef MYHEADER_H
#define MYHEADER_H
// ...
#endif

• And at last, if you have any questions, visit us on IRC (see the readme)!