HACKING.md

Coding style guidelines

The coding style guidelines for Chocolate Doom are designed to keep the style of the original source code. This maintains consistency throughout the program, and does not require the original code to be changed. Some of these guidelines are stricter than what was done in the original source; follow these when writing new code only: there is no need to change existing code to fit them.

You should set tabs to display as eight spaces, not four. However, indentation should be four spaces. If possible, do not use tab characters at all. There is a utility called “expand” which will remove tab characters. For the reasoning behind this, see: http://www.jwz.org/doc/tabs-vs-spaces.html

Please write code to an 80 column limit so that it fits within a standard 80 column terminal. Do not leave trailing whitespace at the end of lines.

Functions should be named like this: AB_FunctionName. The AB prefix denotes the subsystem (AM_ for automap, G_ for game, etc). If a function is static, you can omit the prefix and just name it like FunctionName. Functions and global variables should always be made static if possible.

Put _t on the end of types created with typedef. Type names like this should be all lowercase and have the subsystem name at the start. An example of this is txt_window_t. When creating structures, always typedef them.

Do not use Hungarian notation.

Do not use the goto statement.

Use C++-style comments, ie. // comments, not /* ... */ comments. I don’t care that this isn’t standard ANSI C.

Variables should be named like this: my_variable_name, not like this: MyVariableName. In pointer variable declarations, place the * next to the variable name, not the type.

When casting variables from one type to another, put a space after the last closing brace.

When using an if, do, while, or for statement, always use the { } braces even when they are not necessary. For example, do this:

if (condition)
{
    body;
}

Not this:

if (condition)   // NO
    body;

Write code like this:

typedef struct
{
    int member1;
    char *member2;
} my_structure_t;

void FunctionName(int argument, int arg2, int arg3, int arg4, int arg5,
                  int arg6, int arg7)
{
    int assign_var;

    assign_var = arg2 + arg3 * arg4 * (arg5 + arg6);

    if (foo && !bar || baz && qux || !(foo && bar && baz))
    {
        body;
    }
    else if (xyz + 4 < abc * 4 + 3)
    {
        body;
    }
    else
    {
        body;
    }

    if (very_long_condition_like_this_one_that_forces_a_line_break
     && other_condition)
    {
        body;
    }

    switch (argument)
    {
        case FIRST:
            code;
            break;

        case SECOND:
            code;
            break;

        default:
            break;
    }

    for (a = 0; a < 10; ++a)
    {
        FunctionCall(arg1, arg2, arg3, arg4,
                     arg_split_onto_second_line);
    }

    while (a < 10)
    {
        loop_body;
    }

    do
    {

    } while (condition);
}

Security

The C standard library has a number of unsafe functions that should be avoided when writing code for Chocolate Doom. These are:

Unsafe function	Safer alternative
gets()	fgets(.., stdin)
sprintf	M_snprintf()
snprintf	M_snprintf()
vsprintf	M_vsnprintf()
vsnprintf	M_vsnprintf()
strcpy()	M_StringCopy()
strncpy()	M_StringCopy()
strcat()	M_StringConcat()
strncat()	M_StringConcat()
strdup()	M_StringDuplicate()
realloc()	I_Realloc()

Lots of the code includes calls to DEH_String() to simulate string replacement by the Dehacked tool. Be careful when using Dehacked replacements of printf format strings. For example, do not do this:

printf(DEH_String("foo %s"), s);
sprintf(mybuf, DEH_String("bar %s"), t);

Instead do this:

DEH_printf("foo %s", s);
DEH_snprintf(mybuf, sizeof(mybuf), "bar %s", t);

This does the format string replacement safely in a way that checks the arguments securely.

Portability

Chocolate Doom is designed to be cross-platform and work on different Operating Systems and processors. Bear this in mind when writing code.

Do not use the long type (its size differs across platforms; use int or int64_t depending on which you want).

Use Doom’s byte data type for byte data. int is assumed to be a 32-bit integer, and short is a 16-bit integer. You can also use the ISO C99 data types: intN_t and uintN_t where N is 8, 16, 32, 64.

Be careful with platform dependencies: do not use Windows API functions, for example. Use SDL where possible.

Preprocessor #defines are set that can be used to identify the OS if necessary: _WIN32 for Windows and __MACOSX__ for Mac OS X. Others are set through SDL. Try to avoid this if possible.

Be careful of endianness! Doom has SHORT() and LONG() macros that do endianness conversion. Never assume that integer types have a particular byte ordering. Similarly, never assume that fields inside a structure are aligned in a particular way. This is most relevant when reading or writing data to a file or a network pipe.

For signed integers, you shouldn’t assume that (i >> n) is the same as (i / (1 << n)). However, most processors handle bitshifts of signed integers properly, so it’s not a huge problem.

GNU GPL and licensing

All code submitted to the project must be licensed under the GNU GPLv2 or a compatible license. If you use code that you haven’t 100% written yourself, say so. Add a copyright header to the start of every file. Use this template:

//
// Copyright(C) YEAR Author's name
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
//
// *File description goes here*
//