wxWidgets/docs/contributing/how-to-add-new-wxUSE_XXX.md
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git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76690 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
2014-06-11 21:14:09 +00:00

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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. Files to update
------------------
The following files need to be modified when adding a new `wxUSE_FOO`:
a) 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).
a') include/wx/msw/setup_inc.h for MSW-specific options
This file contains MSW-specific options, so if the new option is only used
under MSW, add it here instead of include/wx/setup_inc.h. The rest of the
instructions is the same as above.
b) include/wx/chkconf.h
Add the check for `wxUSE_FOO` definedness in the corresponding (base or GUI)
section. Please keep the alphabetic order.
If there are any dependencies, i.e. `wxUSE_FOO` requires `wxUSE_BAR` and
`wxUSE_BAZ`, check for thme here too.
b') include/wx/msw/chkconf.h for MSW-specific options
These options won't be defined for the other ports, so shouldn't be added to
the common include/wx/chkconf.h but to this file instead.
c) 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.
d) docs/doxygen/mainpages/const_wxusedef.h
Add a brief description of the new constant.