               How to add a new wxUSE_XXX preprocessor constant
               ================================================

0. Purpose
----------

Detailed description of what needs to be done when you want to add a new
wxUSE_XXX compilation flag. The text below assumes you need new wxUSE_FOO.


1. Overview
-----------

wxWidgets uses wxUSE_XXX macros for conditionally compiling in (or not)
optional components. In general, whenever a new non critical (i.e. not
absolutely required by important parts of the library) class Foo is added it
should use its own wxUSE_FOO compilation flag.

wxUSE_FOO must be always defined and have value of 0 or 1. Be careful with
testing for it in wx/foo.h: don't do it at the very beginning of the file
because then wxUSE_FOO would be not defined at all if the user directly
includes wx/foo.h, include "wx/defs.h" before testing for wxUSE_FOO.


2. Required files update
------------------------

Assuming wxUSE_FOO is used on all platforms, the following must be done:

a) update include/wx/setup_inc.h

   This file contains all common wxUSE_XXXs, and is used to update wxMSW, wxMac
   setup.h and Unix setup.h.in using build/update-setup-h. Please try to add
   the new define in a logical place (i.e. near any related ones) and write a
   detailed comment explaining what does it do and why would you want to turn
   it on/off. Choose the appropriate default value: this should be usually 1
   but can be 0 if there are some problems preventing the use of Foo by default
   (e.g. it requires installation of some non standard 3rd party libraries).
   After changing this file, run the update-setup-h script (this is probably
   better done on a Unix machine although it should work under Cygwin too).

b) update other setup.h files

   Currently include/wx/univ/setup.h and setup.h_vms are not automatically
   updated so please update them manually (or modify the update-setup-h script
   to take care of them...).

c) update configure.in

   Here you need to add DEFAULT_wxUSE_FOO define. It should be added in the
   block beginning after WX_ARG_CACHE_INIT line and should default to "no" for
   "if DEBUG_CONFIGURE = 1" branch (this is used for absolutely minimal builds)
   and the same as default value in setup_inc.h in the "else" branch.

   You also need to add a WX_ARG_ENABLE (or, if new functionality can be
   reasonably described as support for a 3rd party library, WX_ARG_WITH)
   line togetherw with all the existing WX_ARG_ENABLEs.

   If you have a sample/foo which should be only built when wxUSE_FOO==1,
   then only add it to the SAMPLES_SUBDIRS if wxUSE_FOO=yes in configure.


3. Documentation
----------------

Currently wxUSE_XXXs are not documented, except for a few important global ones
which are in docs/latex/wx/cppconst.tex. So normally there is nothing to do
(but this could change in the future).


=== EOF ===

Author:  VZ
Version: $Id: tn0021.txt,v 1.1 2007/03/19 18:10:05 daveh Exp $

