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Creating a Cross-Platform Build System Using Bakefile
The 10-minute, do-it-yourself wx project baking guide (with free sample recipes!)

Status: DRAFT
Author: Kevin Ollivier
Date: 2/13/04
License: wxWidgets License
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Supporting many different platforms can be a difficult challenge. The
challenge for wxWidgets is especially great, because it supports a variety of
different compilers and development environments, including MSVC, Borland C++,
MinGW, DevCPP, GNU make/automake, among others. Maintaining such a large
number of different project files and formats can quickly become overwhelming.
To simplify the maintenance of these formats, one of the wxWidgets developers,
Vaclav Slavik, created Bakefile, a XML-based makefile wrapper that generates
all the native project files for wxWidgets. So now, even though wxWidgets
supports all these formats, wxWidgets developers need only update one file -
the Bakefile, and it handles the rest. But Bakefile isn't specific to
wxWidgets in any way - you can use Bakefile for your own projects, too. This
brief tutorial will take a look at how to do that. 

Note that this tutorial assumes that you are familiar with how to build
software using one of the supported Bakefile makefile systems, that you have
some basic familiarity with how makefiles work, and that you are capable of
setting environment variables on your platform. Also note that the terms Unix
and Unix-based refers to all operating systems that share a Unix heritage,
including FreeBSD, Linux, Mac OS X, and various other operating systems.

-- Getting Started --

First, you'll need to install Bakefile. You can always find the latest version
for download online at http://bakefile.sf.net. A binary installer is provided
for Windows users, while users of Unix-based operating systems (OS) will need
to unpack the tarball and run configure && make && make install. (Packages for
some distros are also available, check http://bakefile.sf.net for details.)

-- Setting Up Your wx Build Environment --

Before you can build wxWidgets software using Bakefile or any other build
system, you need to make sure that wxWidgets is built and that wxWidgets
projects can find the wxWidgets includes and library files. wxWidgets build
instructions can be found by going to the docs subfolder, then looking for the
subfolder that corresponds to your platform (i.e. msw, gtk, mac) and reading
"install.txt" there. Once you've done that, here are some extra steps you
should take to make sure your Bakefile projects work with wxWidgets:

On Windows
----------
Once you've built wxWidgets, you should create an environment variable named
WXWIN and set it to the home folder of your wxWidgets source tree. (If you use
the command line to build, you can also set or override WXWIN at build time by
passing it in as an option to your makefile.)

On Unix
-------
In a standard install, you need not do anything so long as wx-config is on
your PATH. wx-config is all you need. (See the section of the book on using
wx-config for more information.)

-- A Sample wx Project Bakefile --

Now that everything is setup, it's time to take Bakefile for a test run. I
recommend that you use the wx sample Bakefile to get you started. It can be
found in the 'build/bakefiles/wxpresets/sample' directory in the wxWidgets
source tree. Here is the minimal.bkl Bakefile used in the sample:

minimal.bkl
-------------------------------------------------------------
<?xml version="1.0" ?>
<!-- $Id: bakefile_quickstart.txt,v 1.4 2005/05/31 09:17:06 JS Exp $ -->

<makefile>

    <include file="presets/wx.bkl"/>

    <exe id="minimal" template="wx">
        <app-type>gui</app-type>
        <debug-info>on</debug-info>
        <runtime-libs>dynamic</runtime-libs>
        
        <sources>minimal.cpp</sources>
        
        <wx-lib>core</wx-lib>
        <wx-lib>base</wx-lib>
    </exe>

</makefile>
---------------------------------------------------------------

It's a complete sample ready to be baked, so go into the directory mentioned
above and run the following command: 

On Windows:
bakefile -f msvc -I.. minimal.bkl

On Unix:
bakefile -f gnu -I.. minimal.bkl

It should generate a makefile (makefile.vc or GNUmakefile, respectively) which
you can use to build the software. Just build the software using the command
"nmake -f makefile.vc" or "make -f GNUmakefile" respectively. Now let's take a
look at some of the basic Bakefile concepts that you'll need to know to move
on from here.

-- Project Types --

As mentioned earlier, Bakefile builds makefiles for many different
development environments. The -f option accepts a list of formats that you
would like to build, separated by commas. Valid values are:

    autoconf      GNU autoconf Makefile.in files
    borland       Borland C/C++ makefiles
    cbuilderx     C++ Builder X project files
    dmars         Digital Mars makefiles
    dmars_smake   Digital Mars makefiles for SMAKE
    gnu           GNU toolchain makefiles (Unix)
    mingw         MinGW makefiles (mingw32-make)
    msevc4prj     MS eMbedded Visual C++ 4 project files
    msvc          MS Visual C++ nmake makefiles
    msvc6prj      MS Visual C++ 6.0 project files
    watcom        OpenWatcom makefiles

TIP: autoconf Project Type
---------------------------
You may notice that in the sample folder, there is also a file called
configure.in. That file is the input for autoconf, which creates the configure
scripts that you often see when you build software from source on Unix-based
platforms. People use configure scripts because they make your Unix makefiles
more portable by automatically detecting the right libraries and commands to
use on the user's machine and OS. This is necessary because there are many
Unix-based operating systems and they all are slightly different in various
small ways.

Bakefile does not generate a configure or configure.in script, so if you want
to use configure scripts with your Unix-based software, you will need to learn
how to use autoconf. Unfortunately, this topic deserves a book all its own and
is beyond the scope of this tutorial, but a book on the subject can be found
online at: http://sources.redhat.com/autobook/. Note that you do not need to
use automake when you are using Bakefile, just autoconf, as Bakefile
essentially does the same thing as automake. 
----------------------------

-- Targets --

Every project needs to have a target or targets, specifying what is to be
built. In Bakefile, you specify the target by creating a tag named with the
target type. The possible names for targets are:

    exe         create an executable file
    dll         create a shared library
    lib         create a static library
    module      create a library that is loaded at runtime (i.e. a plugin)

Note the sample above is an "exe" target. Once you create the target, all the
build settings, including flags and linker options, should be placed inside
the target tag, as they are in the sample above.

-- Adding Sources and Includes --

Obviously, you need to be able to add source and include files to your
project. You add sources using the "<sources>" tag (as shown above), and add
include directories using the "<include>" tag. You can add multiple <sources>
and <include> tags to add multiple source files, or you can also add multiple
sources and includes into one tag by separating them with a space, like so:

<sources>minimal.cpp minimal2.cpp minimal3.cpp</sources>

If your sources are in a subfolder of your Bakefile, you use the slash "/"
character to denote directories, even on Windows. (i.e. src/minimal.cpp) For
more options and flags, please consult the Bakefile documentation in the 'doc'
subfolder of Bakefile, or you can also find it on the Bakefile web site.

-- Build Options --

What if you want to offer a DEBUG and a RELEASE build? Or a UNICODE/ANSI
build? You can do this in Bakefile by creating options. To create an option,
use the "<option>" tag. A typical option has three important parts: a name, a
default value, and a comma-separated list of values. For example, here is how
to create a DEBUG option which builds debug by default:

<option name="DEBUG">
    <default-value>1</default-value>
    <values>0 1</values>
</option>

You can then test the value of this option and conditionally set build
settings, flags, etc. For more information on both options and conditional
statements, please refer to the Bakefile documentation.

-- Bakefile Presets/Templates and Includes --

It is common that most projects will reuse certain settings, or options, in
their makefiles. (i.e. DEBUG or static/dynamic library options) Also, it is
common to have to use settings from another project; for example, any project
that uses wxWidgets will need to build using the same flags and options that
wxWidgets was built with. Bakefile makes these things easier by allowing users
to create Bakefile templates, where you can store common settings. 

Bakefile ships with a couple of templates, found in the 'presets' subfolder of
your Bakefile installation. The "simple.bkl" template adds a DEBUG option to
makefiles so you can build in release or debug mode. To add this template to
your project, simply add the tag "<include file="presets/simple.bkl"/>" to the
top of your Bakefile. Then, when creating your target, add the
"template="simple"" attribute to it. Now, once you build the makefile, your
users can write commands like:

nmake -f makefile.vc DEBUG=1

or

make -f GNUmakefile DEBUG=1

In order to build the software in debug mode.

To simplify the building of wxWidgets-based projects, wxWidgets contains a a
set of Bakefiles that automatically configure your build system to be
compatible with wxWidgets. As you'll notice in the sample above, the sample
project uses the wx template. Once you've included the template, your software
will now build with wxWidgets support. 

But since the wx presets don't exist in the Bakefile presets subfolder,
Bakefile needs to know where to find these presets. The "-I" command adds the
wxpresets folder to Bakefile's search path. 

If you regularly include Bakefile presets in places other than the Bakefile
presets folder, then you can set the BAKEFILE_PATHS environment variable so
that Bakefile can find these Bakefiles and include them in your project. This
way you no longer need to specify the -I flag each time you build.

Lastly, it's important to note that the Win 32 wx project Bakefiles come with
some common build options that users can use when building the software. These
options are: 

    Option              Values              Description
    ------              ------              -------------
    WX_SHARED           0(default),1        Specify static or dynamic wx libs
    WX_UNICODE          0(defualt),1        Use ANSI or UNICODE wx libs
    WX_DEBUG            0,1(default)        Use release or debug wx libs
    *WX_VERSION         25,26(default)      Specify version of wx libs

*Note: Any version of wx past 2.5 will be allowed here, so 25/26 is not a
complete list of values. 

These options are not needed under Unix as wx-config can be used to specify
these options.

-- bakefile_gen - Automated Bakefile Scripts --

If you have a large project, you can imagine that the calls to Bakefile would
get more and more complex and unwieldly to manage. For this reason, a script
called bakefile_gen was created, which reads in a .bkgen file that provides
all the commands needed to build all the makefiles your project supports. A
discussion of how to use bakefile_gen is beyond the scope of this tutorial,
but it deserves mention because it can be invaluable to large projects.
Documentation on bakefile_gen can be found in the Bakefile documentation.

-- Conclusion --

This concludes our basic tutorial of the cross-platform Bakefile build system
management tool. From here, please be sure to take a good look at the Bakefile
documentation to see what else it is capable of. Please post questions to the
bakefile-devel@lists.sourceforge.net list, or if you have questions specific
to the wx template Bakefile, send an email to wx-users@lists.wxwidgets.org.

Enjoy using Bakefile!
