GPAC coding style

Introduction
  coding styles only concern the GPAC core library (libgpac), and should be used for external filters and modules development.
  
  AStyle is a code beautifier tool. Code should be compliant with the following pattern provided by AStyle :
  AStyle -r --indent=tab '*.c' '*.h' '*.cpp' '*.hpp'
    
1 Exported symbols 

  1.0 Informative note
  The GF_ or gf_ stands for "gpac framework"

  1.1 typedef of structures - typedef of base types - typedef of functions

All symbols defined within libgpac library and exported for application development purposes shall begin with GF_* 
with the first character of "*" being in capital, regardless of their functionality.
For example, GF_Thread (structure), GF_Err (redefined type), GF_LineCap (enum typedef)
    
All structure typedefs, whether defined (declaration exported through ehaders) or not (declaration intern to the GPAC core lib), must follow
this principle.
Furthermore, typedef of non-exported structure shall only apply to the structure itself, not a pointer to it. 
    typedef struct _my_gpac_thingy *GF_LPMYGPACSTUFF;    /*this is FORBIDDEN*/
    typedef struct _my_gpac_thingy GF_MyGPACStuff;    /*this is OK*/
This will allow easy exporting of structure declaration if needed at some point in the development.


  1.2 constants

All constants (whether #defines or enums) shall be in capital letters and begin with "GF_" and use "_" for word separation
For example, error code GF_BAD_PARAM.

Enums names shall refer to the main module they are used in through a keyword right after the GF_ .
For example, 
  * enums referring to file format (isomedia) will be prefixed by GF_ISOM_
  * enums referring to MPEG-4 OD tools (odf) will be prefixed by GF_ODF_
  
  1.3 functions

All exported functions and pointer to functions shall begin with "gf_". The name shall refer to the main module they are sued in 
through a keyword right after the gf_ when reasonable (gf_isom_, gf_odf_, gf_filter_), or to the tool they refer to (gf_bs_, gf_url, ...)
  
2 Miscalleanous

All exported functions' names shall be in lower case exclusively.
All exported functions' parameters should be in lower case exclusively.
Exported structures may use case in any fashion as long as they respect the rules expressed in section 1 above.
Exported structures member should preferably all be lower case - this may not be feasible for scene graph nodes & like...

All exported header files shall be in lower case
All source files within the gpac core shall be in lower case

All comments should be C-like ones (/**/) not C++ ones (//)
All exported headers documentation should be written with doxygen syntax
All constructor-like functions should be of style gf_zzz_new
All destructor like functions should be of style gf_zzz_del

3 Current structure of the GPAC repository
  
This is a short overview of the gpac source repository. 

- *gpac/applications/*
    various apps of GPAC, including MP4Box, gpac, platform-specific ports and test apps
- *gpac/bin/*
    output path of build system
- *gpac/build/*
    various build systems (MSVC, Android, XCode, ...)
- *gpac/debian/*
    files for debian packaging
- *gpac/extra_lib/*
    external lib directory used by different build systems
- *gpac/include/gpac/*
    all exported files of the lib (high level APIs, full documentation available).
- *gpac/include/gpac/internal/*
    all development files of the lib (low level access).
- *gpac/include/gpac/modules/*
    all module APIs defined in GPAC.
- *gpac/packagers/*
    installer scripts for Windows and OSX
- *gpac/modules/*
    various modules of GPAC (video and audio output, font engine,  sensors, ...)
- *gpac/share/doc*
    doxygen for GPAC
- *gpac/share/doc/idl
    doxygen for JS APIs developped in GPAC
- *gpac/share/doc/man*
    man pages for GPAC
- *gpac/share/gui/*
    BIFS+SVG based GUI used by client.
- *gpac/share/lang/*
    Language files (under development) for GPAC options and help
- *gpac/share/res/*
    various resource files used in installers
- *gpac/share/scripts/*
    various JS scripts used by GPAC.
- *gpac/share/shaders/*
    GLSL shaders used by the compositor.
- *gpac/src/bifs/*
    BInary Format for Scene coding (decoder and encoder) (BIFS tables are with MPEG4Gen application in gpac/applications/generators/MPEG4)
- *gpac/src/compositor/*
    interactive composition engine  for 2D & 3D drawing - handles MPEG-4, X3D/VRML and SVG.
- *gpac/src/crypto/*
    cryptographic tools (AES 128 CBC and CTR only)
- *gpac/src/evg/*
    anti-aliased software rasterizer for 2D vector graphics
- *gpac/src/filter_core/*
    filter engine of GPAC, in charge of filter graph resolution, filter scheduling, packets handling.
- *gpac/src/filters/*
    filters defined in GPAC. This include encoders, decoders, av output, wrapper for GPAC's compositor, ISOBMF, RTP, M2TS muxers and demuxers, etc ...
- *gpac/src/ietf/*
    small RTP/RTSP/SDP library, plus media packetizers.
- *gpac/src/isomedia/*
    ISOBMFF (Iso Base Media File Format), features file reading/writing/editing, precise interleaving, hint track creation and movie fragments (read/write). Includes 3GPP/3GPP2 ,  AVC/SVC, HEVC/L-HEVC and JPEG2000 support.
- *gpac/src/jsmods/*
    Various JavaScript modules
- *gpac/src/laser/*
    MPEG-4 LAsER (Lightweight Application Scene Representation)
- *gpac/src/media_tools/*
    media tools for authoring: ISMA & 3GPP tools, AV parsers, media importing and exporting, hinting ...
- *gpac/src/odf/*
    MPEG-4 Object Descriptor Framework: encoding/decoding of all descriptors, OD codec and OCI codec
- *gpac/src/quickjs/*
    QuickJS javascript engine sources
- *gpac/src/scene_manager/*
    memory representation of the scene, importers (BT/XMT/SWF/QT), dumpers and encoding
- *gpac/src/scenegraph/*
    scene Graph API (MPEG4/VRML/X3D/SVG) - BIFS/VRML/X3D nodes are generated using gpac/applications/generators/*
- *gpac/src/utils/*
    all generic objects used throughout the lib (list, bitstream, thread, mutex...). The OS specific files are prefixed os_* .
- *gpac/testsuite/*
    tests suite for GPAC - this is a GIT submodulen repository URL is https://github.com/gpac/testsuite.

    
