// vim:syntax=doxygen
/**

 \page cmp FLTK Code Management Plan (CMP)

<br><br>
<center><h2>*** WORK IN PROGRESS ***</h2></center>
<br><br>

\section cmp_intro CMP Coding Intro

This document defines the coding standards that all FLTK developers must
follow when developing source code and related documentation for the FLTK
library. The purpose of defining formal standards is to organize and focus
our development efforts, ensure that all developers communicate and develop
software with a common vocabulary/style, and make it possible for us to
generate and release a high-quality GUI toolkit which can be used with a
high degree of confidence.

Much of this file describes existing practices that have been used up
through FLTK 1.1.x, however some new standards have been added for future
code and releases.

\section cmp_communication Communication

The fltk.coredev mailing list/newsgroup are the primary means of communication between developers.
All major design changes must be discussed prior to implementation.

We use GitHub Issues to manage bugs.
Please see the CMP section on Managing GitHub Issues for how developers should manage GitHub issues.

It is wise for all developers to monitor these github related mailing list/newsgroups for bug and commit acitivity:

 - fltk.commit — (nntp/web) All fltk developer commits on GitHub commit. Includes old pre-Oct 2018 SVN commits

 - fltk.issues — (nntp/web) All new/current fltk bugs as GitHub Issues. See "Managing GitHub Issues"

 - fltk.bugs   — (nntp/web) The "Old STR Bug Management System" activity (replaced by GitHub Issues). See "Managing Old STR's"

To monitor these groups, either configure github to cc you on activity, or see the https://www.fltk.org/newsgroups.php page
and use either the web interface or NNTP instructions.

\section cmp_goals Specific Goals

The specific goals of the FLTK are as follows:

 - Develop a C++ GUI toolkit based upon sound object-oriented design principles and experience.
 - Minimize CPU usage (fast).
 - Minimize memory usage (light).
 - Support multiple operating systems and windowing environments, including UNIX/Linux, macOS,
   Microsoft Windows, and X11, using the "native" graphics interfaces.
 - Support OpenGL rendering in environments that provide it.
 - Provide a graphical development environment for designing GUI interfaces, classes, and simple programs.
 - Support UTF-8 text.
 - Support printer rendering in environments that provide it.
 - Support "schemes", "styles", "themes", "skinning", etc. to alter the appearance of widgets
   in the toolkit easily and efficiently. The purpose is to allow applications to tailor their
   appearance to the underlying OS or based upon personal/user preferences.
 - Support newer C++ language features, such as templating via the Standard Template Library
   ("STL"), and certain Standard C++ library interfaces, such as streams. However, FLTK will
   not depend upon such features and interfaces to minimize portability issues.
 - Support intelligent layout of widgets.

Many of these goals are satisfied by FLTK 1.1.x, and many complex
applications have been written using FLTK on a wide range of platforms
and devices.

\section cmp_practices_docs Documentation

All widgets are documented using the Doxygen software; Doxygen comments
are placed in the header file for the class comments and any inline
methods, while non-inline methods should have their comments placed in
the corresponding source file. The purpose of this separation is to place
the comments near the implementation to reduce the possibility of the
documentation getting out of sync with the code.

All widgets must have a corresponding test program which exercises
all widget functionality and can be used to generate image(s) for the
documentation. Complex widgets must have a written tutorial, either as
full text or an outline for later publication

Starting with FLTK 1.3 Doxygen is used for HTML and PDF documentation.

\section cmp_coding_standards Coding Standards

The following is a guide to the coding style that must be used when adding
or modifying code in FLTK. Most of this should be obvious from looking at
the code, but here it all is in one spot.

\section cmp_coding_style General Coding Style

The FLTK code basically follows the K&R coding style. While many of the
developers are not entirely satisfied with this coding style, no one has
volunteered to change all of the FLTK source code (currently about 54,000
lines of code!) to a new style.

The K&R coding style can be summarized with the following example code:

\verbatim
int function(int arg) {
  if (arg != 10) {
    printf("arg = %d\n", arg);
    return (0);
  } else {
    return 1;
  }
}

int function2(int arg) {
  for (int i = 0; i < arg; i++) {
    stuff();
  }
  while (something) {
    stuff();
  }
  switch (arg) {
    case 0:
      stuff_here();
      break;
    case 1: {
      int var;
      stuff_here();
      break;
    }
    case 2:
      stuff();
      /* FALLTHROUGH */
    case 3: simple_stuff1(); break;
    case 4: simple_stuff2(); break;
    default:
      break;
  }
  return (0);
}
\endverbatim

To summarize:

  - All curley braces must open on the same line as the enclosing statement, and close at the same level of indentation.
  - Each block of code must be indented 2 spaces.
  - <b>Tabs are not allowed in source files</b>, please use only spaces for indenting.
  - A space follows all reserved words.
  - A space precedes and follows all operators except prefix and postfix operators (++i, j--, et al).

\section cmp_coding_standards_docs Source File Documentation

Each source file must start with the standard FLTK header containing the
description of the file, and FLTK copyright and license notice:

\verbatim
//
// Some descriptive text for the Fast Light Tool Kit (FLTK).
//
// Copyright 1998-2020 by Bill Spitzak and others.
//
// This library is free software. Distribution and use rights are outlined in
// the file "COPYING" which should have been included with this file. If this
// file is missing or damaged, see the license at:
//
//     https://www.fltk.org/COPYING.php
//
// Please see the following page on how to report bugs and issues:
//
//     https://www.fltk.org/bugs.php
//
\endverbatim

..or the equivalent comment block using the C or other comment delimiters appropriate for the source file language (shell, CMake, etc).

\section cmp_coding_doxygen Doxygen Documentation (Comments)

FLTK 1.3 and up uses Doxygen with the JavaDoc comment style to document all classes, structures, enumerations, methods, and functions. Doxygen comments are \b mandatory for all FLTK header and source files, and no FLTK release will be made without complete documentation of public APIs. Here is an example of the Doxygen comment style:

\verbatim
/**
  The Foo class implements the Foo widget for FLTK.

  This description text appears in the documentation for
  the class and may include HTML tags as desired.
*/

class FL_EXPORT Foo : public Widget {
  int private_data_;

public:
  /**
    Creates a Foo widget with the given position and label.

    This description text appears in the documentation for the
    method's implementation.

    References to parameters \p X, \p Y, \p W, \p H are
    mentioned this way.

    \param[in] X,Y,W,H Position and size of widget
    \param[in] L Optional label (default is 0 for no label)
  */
  Foo(int X, int Y, int W, int H, const char *L = 0) {
    ..implementation here..
  }
};
\endverbatim

Essentially, a comment starting with `/\**` before the class or method defines the documentation for that class or method. These comments should appear in the header file for classes and inline methods and in the code file for non-inline methods.

In addition to Doxygen comments, block comments must be used liberally in the code to describe what is being done. If what you are doing is not "intuitively obvious to a casual observer", add a comment! Remember, you're not the only one that has to read, maintain, and debug the code.

<b>Never</b> use C++ comments in C code files or in header files that may be included from a C program. (Otherwise builds on strict platforms like SGI will fail). Normally, fltk C files have ".c" and ".h" file extensions, and C++ have ".cxx" and ".H". Currently there are a few exceptions; filename.H and Fl_Exports.H both get interpreted by C and C++, so you must use C style comments in those.

\section cmp_general_recommendations General Developer Recommendations

Most important rule: <b>Put Doxygen comments where the code's implementation is.</b>
This means don't put the docs with the prototypes in the .H file, unless that's where the code is implemented.

  - \p class, \p typedef, \p enum, and \p inline docs go in the headers

  - Most other docs go in the source files

  - For doxygen syntax in C++ files, use:
  \verbatim
  /** for standard doxygen comments */
  ///< for short single line post-declaration doxygen comments
  \endverbatim

  - For doxygen syntax in C files, use:
  \verbatim
  /**  for standard doxygen comments */
  /**< for short single line post-declaration doxygen comments */
  \endverbatim

  - Use `\p` for parameters citation in the description

  - Use `\param[in] xxx` and `\param[out] xxx` for input/output parameters.

  - Don't use doxygen tags between the `\\htmlonly` and `\\endhtmlonly` pair of tags.

  - When commenting out code or writing non-doxygen comments, be sure not to accidentally use doxygen comment styles, or your comments will be published..! Beware doxygen recognizes other comment styles for itself:
  \verbatim
  /*! beware */
  /*@ beware */
  //! beware
  //@ beware
  \endverbatim

  There may be others. For this reason, follow all non-doxygen comment leaders with a space to avoid accidental doxygen parsing:

  \verbatim
  /* safe from doxygen */
  // safe from doxygen
    ↑
    Space immediately after comment characters
  \endverbatim

  Note: Several characters are 'special' within doxygen commments, and must be escaped with a backslash to appear in the docs correctly. Some of these are:

  \verbatim
  \<    -- disambiguates html tags
  \>    -- ""
  \&    -- ""
  \@    -- disambiguates JavaDoc doxygen comments
  \$    -- disambiguates environment variable expansions
  \#    -- disambiguates references to documented entities
  \%    -- prevents auto-linking
  \\   -- escapes the escape character
  \endverbatim

  - Itemized lists can be specified two ways; both work, left is preferred:

<table>
  <tr><th> Preferred </th> <th> Old </th></tr>
  <tr><td>
  \verbatim
  /**
   Here's a bullet list:

   - Apples
   - Oranges

   Here's a numbered list:

   -# First thing
   -# Second thing

 */
  \endverbatim
  </td><td>
  \verbatim
  /**
   Here's a bullet list:
   <ul>
     <li> Apples</li>
     <li> Oranges</li>
   </ul>
   Here's a numbered list:
   <ol>
     <li> First thing</li>
     <li> Second thing</li>
   <ol>
  */
   \endverbatim
  </td></tr>
</table>

\section cmp_temporary_code Documenting Temporary Code or Issues

Temporary code and code that has a known issue MUST be documented in-line with the following (Doxygen) comment style:

\verbatim
  /** \todo this code is temporary */
\endverbatim

<b>`\todo`</b> items are listed by Doxygen making it easy to locate any code that has an outstanding issue or code that should be removed or commented out prior to a release.

\section cmp_documenting_class_and_struct Documenting Classes and Structures

Classes and structures start with a comment block that looks like the following:

\verbatim
/**
  A brief description of the class/structure.

  A complete description of the class/structure.
*/
class MyClass {
  ...implementation...
};
\endverbatim

\section cmp_documenting_enum Documenting Enumerations

Enumerations start with a comment block that looks like the following:

\verbatim
/**
  A brief description of the enumeration.

  A complete description of the enumeration.
*/
enum MyEnum {
  ...implementation...
};
\endverbatim

Each enumeration value must be documented in-line next to the corresponding definition as follows:

\verbatim
/* C++ STYLE */
enum MyEnum {
  BLACK,    ///< The color black.
  RED,      ///< The color red.
  GREEN,    ///< The color green.
  YELLOW,   ///< The color yellow.
  BLUE      ///< The color blue.
};
\endverbatim

If the enum is included in a C file, be sure to use C style commenting:

\verbatim
/* C STYLE */
enum MyEnum {
  BLACK,    /**< The color black. */
  RED,      /**< The color red. */
  GREEN,    /**< The color green. */
  YELLOW,   /**< The color yellow. */
  BLUE      /**< The color blue. */
};
\endverbatim

\section cmp_documenting_functions_and_methods Documenting Functions and Methods

Functions and methods start with a comment block that looks like the following:

\verbatim
/**
  A brief description of the function/method.

  A complete description of the function/method.
  Optional passing mention of parameter \p a and \p out1.

  Optional code example goes here if needed:
  \code
  ..code showing how to use it..
  \endcode

  \param[in] a Description of input variable a
  \param[in] x,y Description of input variables x and y in one comment
  \param[out] out1 Description of output variable out1
  \param[out] out2 Description of output variable out2
  \return 0 on success, -1 on error
  \see other_func1(), other_func2()
*/
int my_function(int a, int x, int y, float &out1, float &out2) {
  ...implementation...
}
\endverbatim

Some details on the above:

- <b>Parameters</b>

  Use `\param` to document function/method parameters using either of the following formats, the latter being preferred:

  \verbatim
  \param var Some description
  \param[in|out] var Some description.
  \endverbatim

  Mention of parameters in docs should use `"\p varname"`. (Use `\p` instead of `\a`)

  Note: Doxygen checks your `\param` variable names against the actual function signatures in your code.
  It does NOT check `\p` names for consistency.

- <b>Return Values</b>

  Use `\return` to document return values. Omit this if there is no return value.

- <b>Reference related methods</b>

  Use `\see` to help the reader find related methods.
  (Methods are sorted alphabetically by doxygen, so 'related' methods might not appear together)

  Locate `\see` references below `\param[]` and `\return` as shown in the above example.

- <b>Code examples</b>

  Use `\code` and `\endcode` when code examples are needed.
  Text within will be exempt from html and doxygen escape code parsing,
  so you don't have to escape characters \<, \>, \&, etc. as you would normally.

  Be careful not to embed C style comments within `\code` and `\endcode` or it
  will break the outer doxygen comment block. (A good reason to always test
  build the code base before commiting documentation-only mods)

- <b>Where to put docs</b>

  Function/method documentation must be placed next to the corresponding code.
  (Rule: "Put the docs where the code implementation is.")
  Comments for in-line functions and methods are placed in the header file where they're defined.

\section cmp_documenting_members_and_variables Documenting Members and Variables

Members and variables can be documented in one of two ways; in block comment form:

\verbatim
/**
  A brief doxygen description of the member/variable.

  A complete description of the member/variable.
  More text goes here..
*/
int my_variable_;
\endverbatim

or in the preferred form as in-line comments as follows:

\verbatim
int my_variable1_;    ///< C++ file's brief doxygen description of the member/variable
int my_variable2_;    /**< C file's brief doxygen description of the member/variable */
\endverbatim

\section cmp_methodology_algorithms Methodology, Algorithms, Etc.

The goal of FLTK is to provide a robust GUI toolkit that is small, fast,
and reliable. All public API functions and methods must be documented with
the valid values for all input parameters - NULL pointers, number ranges,
etc. - and no public API function may have undefined behaviors. Input
validation should be performed only when the function or method is able
to return an error to the caller.

When solving a particular problem, whether you are writing a widget or adding
functionality to the library, please consider the following guidelines:

  -# Choose the small, simple, easy-to-test algorithm over a more complex, larger one that is harder to debug and maintain.
  -# Choose the fastest algorithm that satisfies #1
  -# Break complex solutions into smaller, more manageable pieces.
  -# If functionality can be separated from the main part of the FLTK library, separate it. The idea is to keep the FLTK "core" as small as possible so that programs use memory proportionate to their complexity rather than starting big.
  -# Choose a general-purpose solution over a single-purpose solution, i.e. don't limit your design to what you think something will be used for.
  -# Don't rely on functionality available on a particular platform or compiler; this ties in with #5.

\section cmp_portability C++ Portability

Since FLTK is targeted at platforms which often lack complete ISO C++
support or have limited memory, all C++ code in FLTK must use a subset
of ISO C++. These restrictions shall be reviewed prior to each minor or
major release of FLTK.

\subsection cmp_fltk_1_1_x_restrictions FLTK 1.1.x Restrictions

The following C++ features may be not used in FLTK 1.1.x code:

  - Exceptions
  - Namespaces
  - Standard C++ headers and library
  - Templates
  - static_cast, dynamic_cast, const_cast

\subsection cmp_fltk_1_3_x_restrictions FLTK 1.3.x Restrictions

The following C++ features may be not used in FLTK 1.3.x code:

  - Exceptions
  - Namespaces
  - Standard C++ headers and library
  - Templates
  - dynamic_cast

\subsection cmp_fltk_1_4_x_restrictions FLTK 1.4.x Restrictions

The following C++ features may be not used in FLTK 1.4.x code:

  - Exceptions
  - Namespaces
  - Standard C++ headers and library
  - Templates
  - dynamic_cast

The `reinterpret_cast` keyword may be used but is not mandatory.

The `static_cast` and `const_cast` keywords should be used when casting pointers of different types.

The `dynamic_cast` keyword must not be used since run-time typing features may not be available at all times.

\subsection cmp_fltk_1_5_x_restrictions FLTK 1.5.x Restrictions

\todo This needs to be populated with the new restrictions/allowed c++ features.

\subsection cmp_source_file_naming Source File Naming

The current practice is to use an extension of ".c" for C source files,
".h" for C header files, ".cxx" for C++ source files, and ".H" for C++
header files in the "FL" directory (".h" otherwise.)

\todo Mention of the "fltk" namespace below is I think fltk2 specific, needs changes for 1.x.x

Function/Method/Variable Naming

All public (exported) functions and variables must be placed in the
"fltk" namespace. Except for constructor and destructor methods, the
names consist of lowercase words separated by the underscore ("_"),
e.g. "fltk::some_variable" and "text_color()". Private member variables
of classes end with an extra underscore, e.g. "text_size_".

\section cmp_struct_class_naming Structure/Class Naming

\todo The following needs modification; AFAIK we don't use the `fltk`
      namespace - I think that was an fltk2 thing - but we do recently
      make some use of `Fl` namespace (matt's recent tablet commits)

All public (exported) structures and classes must be placed in the
"fltk" namespace and consist of capitalized words without the underscore,
e.g. "fltk::SuperWidget".

Private members of classes must end with a trailing underscore ("_")
and have corresponding public access methods without the underscore as
applicable, e.g. "text_size_" and "text_size()".

\section cmp_constant_enum_naming Constant/Enumeration Naming

\todo The following needs modification regarding "fltk" namespace
      (this being an FLTK2 thing IIRC)

Public enumerations and constant variables must be placed inside the "fltk"
namespace and consist of UPPERCASE WORDS separated by the underscore ("_"),
e.g. "ALIGN_LEFT", "COLOR_RED", etc. Enumeration type names consist of
capitalized words without underscores, e.g. "MyEnum". `#define` constants
are prohibited aside from the include guard definitions.

\section cmp_preprocessor_variables Preprocessor Variables

\todo In the following, references to `config.h` should be limited to 1.4.x
      and back(?) and newer code to `fl_config.h`? I'm not sure when we
      switched to fl_config.h, but that should maybe be mentioned somewhere in the CMP.

File config.h and the C++ compilers define a few preprocessor variables
that help organizing platform-specific code and control access to a few
internal classes. Only code internal to the FLTK library can include the
config.h header file. Thus, FLTK header files that are part of the public
API must not, directly or indirectly, include config.h.

  - `_WIN32` identifies the MS-Windows platform (both for the 32- and 64-bit versions).
  Note: FLTK 1.3.x used WIN32 which had to be defined by the FLTK build system whereas
  FLTK 1.4 uses `_WIN32` (with leading underscore) which should be defined by the
  build tools (preprocessor, compiler) on the Windows platform.
  <br><br>
  - `__CYGWIN__` is defined when FLTK runs on Windows but uses Cygwin's POSIX
  emulation features (cygwin1.dll).
  <br><br>
  - `__APPLE__` identifies the macOS platform.

  \todo The following needs updating - I think Quartz stuff was Cocoa-ized?
        Might need to at least refer to the FLTK versions for when quartz was
        replaced w/cocoa.

  <br><br>
  - `__APPLE_QUARTZ__` is defined by config.h for the macOS platform.
  At present, use of `__APPLE_QUARTZ__` is equivalent to using `__APPLE__`.
  This may change in the future if other graphics systems than Quartz are
  supported on the macOS platform.

  \todo In the following, reference to `configure` and `config.h` should
        perhaps be qualified with reference to 1.4.x and back?

  <br><br>
  - `USE_X11` is defined by config.h when Xlib is the graphics system used.
  Thus, `USE_X11` is defined on all Unix and Linux platforms, and on Windows,
  if `configure` used `--enable-cygwin` and `--enable-x11`.  Xlib-specific
  code is also often delimited without reference to the `USE_X11` variable
  (thus without the requirement to include config.h) as follows:
  \verbatim
  #if defined(WIN32)
  #elif defined(__APPLE__)
  #else
  .. Xlib specific code ...
  #endif
  \endverbatim

  \todo In the following, config.h. -> fl_config.h..

  <br><br>
  - `USE_XFT` is defined by `config.h` when `USE_X11` is defined.
  It is set to 1 when the Xft library of scalable, anti-aliased fonts is
  used, and to 0 otherwise.
  <br><br>
  - `FL_LIBRARY` is defined by all FLTK library build systems when the
  FLTK library itself is compiled. Application program developers should
  not define it when compiling their programs.
  <br><br>
  - `FL_DLL` is defined by the FLTK build system when building shared
  libraries (DLL's) with Visual Studio. Application program developers
  using Visual Studio and linking against the shared FLTK libraries (DLL's)
  built with Visual Studio must define this macro when compiling their
  source files. Note that this macro must be defined by the build system
  (VS project setup/properties) or on the compiler command line so it is
  "seen" by all included FLTK header files.
  <br><br>
  - `FL_INTERNALS` can be defined by application program developers to
  access certain internal FLTK library classes (e.g., the `Fl_X` class)
  if they need it. APIs to these internal classes are highly subject to
  changes, though.
  <br><br>
  - `FL_DOXYGEN` is defined when the Doxygen program that builds the FLTK
  documentation processes the source code. This variable has two major uses:
  <br><br>
   -# `#ifndef FL_DOXYGEN` / `#endif` allows to hide code from Doxygen.
   -# The Doxygen program does not define the platform-specific variables
   `__APPLE__` or `_WIN32` (even if it's run on macOS or Windows).
   Thus, platform-specific (say, macOS-specific) code must be bracketed
   as follows to be seen by Doxygen:
   \verbatim
   #if defined(__APPLE__) || defined(FL_DOXYGEN)
   ... Doxygen-visible, macOS-specific code ...
   #endif
   \endverbatim
  <br><br>
  - `FL_ABI_VERSION` is used to allow developers to implement ABI breaking code
  in Patch Releases. Normally set to the default ABI version for each minor
  version (for instance 10400 for all 1.4.x releases), can be changed by
  users or devs with configure or CMake to enable ABI breaking features
  for testing or use by end users in static builds of FLTK.
  <br><br>
  Note: This preprocessor variable was named FLTK_ABI_VERSION in FLTK
  1.3.x and was renamed to FL_ABI_VERSION since FLTK 1.4.0.
  <br><br>
  When set, the variable's value is expected to be the integer representation
  of the FLTK version number, where the Minor and Patch numbers are padded
  to two digits to allow for numbers 1 thru 99, e.g.
  \verbatim
  #define FL_ABI_VERSION 10401    // FLTK ABI version 1.4.1
        ..'1' is the major version (no padding; avoids octal issues)
        ..'04' is the minor version (2 digit padding)
        ..'01' is the patch version (2 digit padding)
  \endverbatim
  ABI breaking features are by default '\#ifdef'ed out with this variable
  during patch releases, and are merged in by developers during the next
  Minor Release.
  <br><br>
  Example: If the current patch release is 1.4.0, and the developer adds
  an ABI-breaking fix to what will be the next 1.4.1 release, then the
  new code would be implemented as:
  \verbatim
  #if FL_ABI_VERSION >= 10401  // FLTK 1.4.1, the next patch release #
  ... new ABI breaking code ...
  #else
  ... old non-ABI breaking (default builds) ...
  #endif
  \endverbatim
  This variable solves several issues:
   - Allows ABI breaking code to be implemented at any time by developers.
   - Gets fixes into Git sooner, so users can see, test and access it.
   - Testing ABI features during Patch Releases increases the stability of Minor Releases.
   - Prevents devs having to defer ABI breaking code to the small window of time preceding Minor Releases.

\section cmp_miscellaneous_coding_practices Miscellaneous Coding Practices

\todo In the following I had to use special unicode chars for the C comment
      `∕* FALLTHROUGH *∕` because I couldn't figure out how to escape the
      ascii equivalent in this context; escaping the asterisk wasn't working.
      The use unicode looks right but is a problem if someone copy/pastes
      this verbatim into source code. Open to suggs on how to properly escape this.
      Unfortunately doxygen doesn't support html hex syntax, e.g. '`&#xx;`'

\subsection cmp_use_of_fallthrough Using switch() ∕* FALLTHROUGH *∕

When using switch/case statements, and your case statement does not end in
break in order to fall through to the next case statement, a `∕* FALLTHROUGH *∕`
comment should be added where the break statement would be.

\subsection cmp_useful_vs_macros Useful Visual Studio C++ Macros (Windows)

Here's a list of Visual Studio compiler macros that can be used to
conditionalize code based on the Visual Studio version:

        VERSION     MACRO            PRODUCT NAME
        -------     ---------------- --------------------
        MSVC++ 16.0 _MSC_VER == 1920 Visual Studio 2019
        MSVC++ 15.0 _MSC_VER == 1910 Visual Studio 2017
        MSVC++ 14.0 _MSC_VER == 1900 Visual Studio 2015
        MSVC++ 12.0 _MSC_VER == 1800 Visual Studio 2013
        MSVC++ 11.0 _MSC_VER == 1700 Visual Studio 2012
        MSVC++ 10.0 _MSC_VER == 1600 Visual Studio 2010
        MSVC++ 9.0  _MSC_VER == 1500 Visual Studio 2008
        MSVC++ 8.0  _MSC_VER == 1400 Visual Studio 2005
        MSVC++ 7.1  _MSC_VER == 1310 Visual Studio 2003
        MSVC++ 7.0  _MSC_VER == 1300 Visual Studio 7
        MSVC++ 6.0  _MSC_VER == 1200 Visual Studio 6
        MSVC++ 5.0  _MSC_VER == 1100 Visual Studio 5

Recommended usage:

\verbatim
#if defined(_MSC_VER) && (_MSC_VER <= 1300)             /* VS7 and older */
  ..
#else  /* _MSC_VER */
  ..
#endif /* _MSC_VER */
\endverbatim

\subsection cmp_useful_xcode_macros Useful Xcode C++ Macros (macOS)

Here's a list of operating system version compiler macros that can be
used to conditionalize code based on the compile time version of the macOS
operating system.

These are made available from Apple's `AvailabilityMacros.h`. For more info
on these and other macros, see Apple's "TechNote 2064".

    VERSION     MACRO                   VALUE    PRODUCT NAME
    -------     ---------------------   -----    --------------------
    10.0        MAC_OS_X_VERSION_10_0    1000    Cheetah
    10.1        MAC_OS_X_VERSION_10_1    1010    Puma
    10.2        MAC_OS_X_VERSION_10_2    1020    Jaguar
    10.3        MAC_OS_X_VERSION_10_3    1030    Panther
    10.4        MAC_OS_X_VERSION_10_4    1040    Tiger
    10.5        MAC_OS_X_VERSION_10_5    1050    Leopard
    10.6        MAC_OS_X_VERSION_10_6    1060    Snow Leopard
    10.7        MAC_OS_X_VERSION_10_7    1070    Lion
    10.8        MAC_OS_X_VERSION_10_8    1080    Mountain Lion
    10.9        MAC_OS_X_VERSION_10_9    1090    Mavericks
    10.10       MAC_OS_X_VERSION_10_10 101000    Yosemite
    10.11       MAC_OS_X_VERSION_10_11 101100    El Capitan
    10.12       MAC_OS_X_VERSION_10_12 101200    Sierra
    etc..

Recommended usage:

\verbatim
#include <FL/platform.H> // defines the MAC_OS_X_VERSION_10_xx macros
#if (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_5)
if (fl_mac_os_version >= 100500) {
  ..10.5 and newer..
} else
#else
{
  ..10.4 and older..
}
#endif
\endverbatim

This way, code compiled before and after macOS 10.5 will be able to run
on computers running macOS versions before and after 10.5.

\subsection cmp_useful_gnu_macros Useful GNU C++ Macros

\todo To be done.

\section cmp_coding_source_files Source Files

Each source file shall be placed a sub-directory corresponding to the software sub-system it belongs to ("fltk", "OpenGL", etc.) To remain compatible with case-insensitive filesystems, no two directory names shall differ only by the case of the letters in the name.

Source files shall be documented and formatted as described in the Coding Standards section. To remain compatible with case-insensitive filesystems, no two filenames shall differ only by the case of the letters in the name.

C source files shall have an extension of ".c". C++ source files shall have an extension of ".cxx". Header files shall have an extension of ".h" unless used for FLTK 1.x compatibility. FLTK 1.x compatibility headers shall have an extension of ".H".

  <table>
    <tr><th><center>
      <b>Why use the ".cxx" extension?</b>
    </center></th></tr><tr><td>
      C++ source files can have any of the following extensions on various
      platforms: ".C", ".cc", ".cpp", ".cxx". Only the ".cxx" extension is
      universally recognized by C++ compilers as a C++ source file - ".C"
      is not usable on macOS and Windows, ".cc" is not usable on Windows, and
      ".cpp" is historically considered C preprocessor output on UNIX.
      <p>
      Since not all make programs handle C++ source files with the ".cxx"
      extension, the FLTK build system explicitly defines makefile rules
      for compiling C++ source files with an extension of ".cxx".
    </td></tr>
  </table>

IDE/compiler support source files (project files, workspaces, makefiles, etc.) shall have extensions as required by the IDE/compiler tool.

Header files must utilitize so-called "guard" definitions to prevent multiple inclusion. The guard definitions are named using the full path in the FLTK source tree, e.g.:

    FL/Fl.H becomes _FL_Fl_H_
    fluid/foo.h becomes _fluid_foo_h_

Any non-alphanumeric (letters and numbers) characters are replaced with the underscore (_) character, and leading and trailing underscores are added to limit global namespace pollution.

\section cmp_practices_cmake Build System (CMake)

The FLTK build system uses CMake to tailor the library to the local operating
system. Since FLTK 1.4 the primary and recommended build system is CMake. The
older autoconf/configure builds are no longer supported as of FLTK 1.5.x.

To improve portability, makefiles must not make use of the unique features
offered by GNU make. See the Makefile Standards section for a description
of the allowed make features and makefile guidelines.

Additional GNU build programs such as GNU automake and GNU libtool must
not be used. GNU automake produces non-portable makefiles which depend
on GNU-specific extensions, and GNU libtool is not portable or reliable
enough for FLTK.

Note: Starting with FLTK 1.4.0 we do no longer bundle IDE files for
Microsoft Windows (Visual Studio) and macOS (Xcode). IDE environments
(project files) can be generated with CMake. See README.CMake.txt for more
information about using CMake.

*/