gimp/HACKING

Requirements
------------
If you want to hack on the GIMP project, it will make your life easier
to have the following packages (or newer versions) installed:

    * GNU autoconf 2.54
        - ftp://ftp.gnu.org/gnu/autoconf/
    * GNU automake 1.9 (automake 1.10 should also work)
        - ftp://ftp.gnu.org/gnu/automake/
    * GNU libtool 1.5
        - ftp://ftp.gnu.org/gnu/libtool/

Fine GNU mirrors are listed at https://www.gnu.org/prep/ftp.html
Beta software can be found at alpha.gnu.org.

    * pkg-config 0.16.0 (or preferably a newer version)
        - https://www.freedesktop.org/software/pkgconfig/

    * gtkdocize
        - https://ftp.gnome.org/pub/GNOME/sources/gtk-doc/

    * xsltproc
        - ftp://ftp.gnome.org/pub/GNOME/sources/libxslt/1.1/

These are only the additional requirements if you want to compile from
the git repository. The file INSTALL lists the various libraries we
depend on.


Compilation
-----------
If you are accessing gimp via git, then you will need to take several
steps to get it to compile.  You can do all these steps at once by
running:

    gimp/trunk$ ./autogen.sh

Basically this does the following for you:

    gimp/trunk$ aclocal-1.9; libtoolize; automake-1.9 -a;
    gimp/trunk$ autoconf; intltoolize --automake

The above commands create the "configure" script.  Now you can run the
configure script in gimp/trunk to create all the Makefiles.

Before running autogen.sh or configure, make sure you have libtool in
your path. Also make sure glib-2.0.m4 glib-gettext.m4, gtk-2.0.m4,
pkg.m4 and intltool.m4 are either installed in the same
$prefix/share/aclocal relative to your automake/aclocal installation
or call autogen.sh as follows:

    $ ACLOCAL_FLAGS="-I $prefix/share/aclocal" ./autogen.sh

Note that autogen.sh runs configure for you.  If you wish to pass
options like --prefix=/usr to configure you can give those options to
autogen.sh and they will be passed on to configure.

If AUTOGEN_CONFIGURE_ARGS is set, these options will also be passed to
the configure script. If for example you want to enable the build of
the GIMP API reference manuals, you can set AUTOGEN_CONFIGURE_ARGS to
"--enable-gtk-doc". Please note that you will then need a recent
version of gtk-doc as well as a working setup for handling DocBook/XML.

If you do not have a recent version of gtk-doc, you can pass the
option "--disable-gtk-doc" to autogen.sh.  This will completely
disable the support for gtk-doc so you will not be able to generate
the API documentation.

If you want to use libraries from a non-standard prefix, you should set
PKG_CONFIG_PATH appropriately. Some libraries do not use pkgconfig, see
the output of ./configure --help for information on what environment
variables to set to point the compiler and linker to the correct path.
Note that you need to do this even if you are installing Gimp itself
into the same prefix as the library.


Git
---
GIMP is available from GNOME Git. You can use the following commands
to get GIMP from the the git server:

    $ git clone https://gitlab.gnome.org/GNOME/gimp.git

You can read more on using GNOME's git service at these URLs:

    https://wiki.gnome.org/Git
    https://www.kernel.org/pub/software/scm/git/docs/


You will also need relatively new stable releases of glib, pango, atk,
gtk+, cairo, gtkhtml2, etc. for building GIMP, which you can get as a
part of recent Linux distribution releases.


Patches
-------

The best way to submit patches is to provide files created with
git-format-patch.

It is recommended that you file a bug report at
https://gitlab.gnome.org/GNOME/gimp
and either create a merge request or attach your patch to it as a plain
text file, not compressed. If your patch is reasonably small you can
submit it to the gimp-developer-list@gnome.org mailing list.

If the patch needs to be discussed, you should also consider using the
mailing list instead of Bugzilla because bug reports tend to be hard
to read if they contain too many comments. For the code, please try to
follow the guidelines given in Hackordnung, below.


Auto-generated Files
--------------------
Please notice that some files in the source are generated from other
sources. All those files have a short notice about being generated
somewhere at the top. Among them are the files ending in pdb.[ch] in
the libgimp directory and the files ending in cmds.c in the app/pdb
subdirectory. Those are generated from the respective .pdb files in
pdb/groups.


Hackordnung
-----------
We encourage you to follow the GIMP coding style throughout the GIMP
project.  For the core components (application and libs) this coding
style is enforced.  The GIMP coding style is defined as follows:

    * There's a single space between the function name and the opening
      paren.

    * Function names are lowercase, words separated by underscores.

    * Macros and enums are all uppercase, words separated by
      underscores.

    * Types are all words capitalized, no separators between words.

    * All functions in header files need to be prototyped.

    * Indentation rules are GNU coding style, in particular:
        - 2 characters indentation level
        - Do not use tabs (of course your editor can accept the TAB key
          as a command, typically to indent the current line properly
          or to add spaces at the cursor until the next multiple of 8
          columns, but it should not put TAB characters in the file).
        - When editing files that still have TABs in them, make sure your
          editor interprets the TABs correctly, that is, has tab stops
          at 8 column intervals.
        - Opening braces are on a new line and indented one level.
        - Function header have the return type on one line, the name
          starting in the first column of the following line. All
          parameters are prototyped and there's a new line for each.

The source tree contains local config files which can be used to set the
right coding style in common editors: `.dir-locals.el` for Emacs,
`.kateconfig` for Kate, and `devel-docs/c.vim` for Vim (check the top
comments to see how to enable it automatically when opening a file in
the GIMP tree).

Try to make use of GLib's object system as much as possible. Do not
create wrappers around functions of parent classes. If you end up
duplicating code, try to create a common parent class and implement
the common methods there.

Don't include headers in headers except where unavoidable (e.g. for
deriving objects). Opaque typedefs go to app/base/base-types.h,
app/core/core-types.h etc. See devel-docs/includes.txt for a
detailed description of the include policy.

Don't use the GTK wrappers around the GLib object and signal system.

One goal of GIMP development is to make the GIMP code more readable
and understandable. Please help us to achieve this goal by cleaning up
the present code and make sure that all new code follows the coding
guidelines.