Difference between revisions of "CMake"

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= What's this about? =
CMake is a system for generating per-platform build files.  Visit [http://cmake.org cmake.org] for general information about CMake.


We're experimenting with the possibility of switching to [http://www.cmake.org/ CMake] for building the Second Life viewer.
Linden Lab switched to CMake for building the Second Life viewer (starting with version 1.21); we are currently using version 2.8.10.2


== Why change what we're doing? ==
= Introduction to CMake =


Our current build system is unsatisfactory in several respects.
CMake has the advantage of generating per-platform build files for us.  On Linux, it will generate Makefiles and KDevelop project files.  On OS X, it will generate Makefiles and Xcode project files.  On Windows, it will generate Makefiles (for nmake) and Visual Studio project files.
 
Within Linden Lab, we use different tools on each platform: [http://www.scons.org/ scons] on Linux, Visual Studio 2003 on Windows, and XCode on OS X.
* Any time we add or rename a source file, updating the various build instructions is painful.
* We can't easily stay up to date with newer tools, such as Visual Studio 2005 or 2008.
* Merging changes to the project files used by XCode and Visual Studio is a nightmare.
 
== What does CMake buy us? ==
 
CMake has the advantage of generating per-platform build files for us.  On Linux, it will generate Makefiles and KDevelop project files.  On OS X, it will generate Makefiles and XCode project files.  On Windows, it will generate Makefiles (for nmake) and Visual Studio project files.


All of the "smarts" stay in the CMake files, so there's just one authoritative source of build knowledge.  This means that people can use the development environment they prefer without having to worry so much about breaking other people's builds.  Because CMake files are plain text, merging is easy, as is maintaining experimental patches.
All of the "smarts" stay in the CMake files, so there's just one authoritative source of build knowledge.  This means that people can use the development environment they prefer without having to worry so much about breaking other people's builds.  Because CMake files are plain text, merging is easy, as is maintaining experimental patches.


CMake instructs your build system in how to rebuild its input files when it detects changes to CMake's configuration files.  This means that you only need to run <code>cmake</code> once.  After that, <code>make</code> or your IDE should keep the CMake files and its own project files in sync for you.
CMake tells your build system how to rebuild its input files when it detects changes to CMake's configuration files.  This means that you only need to run <code>cmake</code> once.  After that, <code>make</code> or your IDE should keep the CMake files and its own project files in sync for you.
 
== What are some downsides to CMake? ==
 
Please note: none of the following caveats is really serious.
 
The CMake configuration language is weird and ugly.
 
The tool has some peculiar inconsistencies: some variables and actions are inherited across files, and others are not.  There's no regularity to these, so you have to bump into them one by one.
 
The documentation is weak.  It's mostly organised as reference documentation that assumes that you already know how to use CMake.  This is a much bigger problem for new projects than ones that have already bit the bullet.  We've already worked through the early "WTF?" stages.  It's much easier to hack on existing CMake files than it is to create new ones from scratch with no prior experience.


= Performing a build with CMake =
= Performing a build with CMake =


First of all, you'll need to [http://www.cmake.org/HTML/Download.html download CMake], and install it.  On Linux distros, it's usually available as a native package.  On Windows and OS X, just use the prebuilt binaries.
Our builds are now managed one layer further out then CMake, using [[Autobuild]]; starting there is recommended.
 
These are Linux/Mac instructions.  The Windows instructions are presumably similar, except you wave your mouse around instead of running commands.
 
Check out a copy of the viewer cmake branch.  <b>NOTE:</b> This does not yet exist!
<pre>
svn co http://svn.secondlife.com/svn/linden/branches/cmake
</pre>
Create a build directory:
<pre>
mkdir mybuild
</pre>
Go into your build directory, and run <code>cmake</code> or <code>ccmake</code> in there, pointing it at the parent directory.  If you want to generate a makefile for use by [http://www.gnu.org/software/make/ GNU Make], the defaults will work.
<pre>
cmake ..
</pre>
If you're on a Mac and want to use XCode, use this command instead.
<pre>
cmake -G XCode ..
</pre>


This does <i>not</i> run a build.  It just generates the makefiles, project files, or whatever that you'll need.  After you're done, you'll have a top-level makefile or project file in your build directory.  Run <code>make</code> or load it into your IDE, and away you go!
Per platform build instructions for CMake-based builds of the Second Life viewer are available for these platforms:
* [[Microsoft Windows Builds|Microsoft Windows]]
* [[Compiling the viewer (Mac OS X)|Mac OS X]]
* [[Compiling the viewer (Linux)|Linux]]


In principle, your build should run to completion.  If you run into any problems, please report them.  Better yet, if you can fix them and supply patches, we'd be thrilled!


== Prebuilt libraries vs. standalone builds ==
= Modifying CMake Files =


While many users will want to use the prebuilt libraries that we provide, we're also interested in making life as easy as possible for packagers who want to use their platform's native libraries.
== What to modify ==


If you run <code>ccmake</code>, you should see a <code>STANDALONE</code> option that determines whether the build will use your system's libraries or our prepackaged ones.  Flipping this to <code>TRUE</code> should be all you need to do to perform a packager-friendly build.
'''TODO'' - discuss structure of CMake files
 
For standalone builds, we'd really like to beef up the checks for system libraries so that for example <code>cmake</code> will fail if a required library (such as OpenJPEG) isn't installed.  We welcome all patches that help out with this.


= Patching guidelines =
= Patching guidelines =
Line 70: Line 32:


If you're sending patches in, please follow a few simple guidelines:
If you're sending patches in, please follow a few simple guidelines:
* Use regular context diffs.
* Follow the existing coding style in the CMake files.  I don't like code shouting at me, so prefer lowercase letters.
* Follow the existing coding style in the CMake files.  I don't like code shouting at me, so prefer lowercase letters.
* One logical change per patch.
* One logical change per patch.
* Use spaces for indentation, not tabs.
* Use spaces for indentation, not tabs.


I'd like to try an experiment with the development process.  Instead of creating JIRA issues, please send your patches to <code>bos at lindenlab dot com</code>, and CC <code>sldev</code>.  Inline patches are preferred over attachments, unless your email client trashes white space (as many do).
See [[Submitting patches]] for more details.
 
[[Category:Open Source Portal]]
[[Category:Compiling viewer]]

Latest revision as of 09:35, 13 February 2013

CMake is a system for generating per-platform build files. Visit cmake.org for general information about CMake.

Linden Lab switched to CMake for building the Second Life viewer (starting with version 1.21); we are currently using version 2.8.10.2

Introduction to CMake

CMake has the advantage of generating per-platform build files for us. On Linux, it will generate Makefiles and KDevelop project files. On OS X, it will generate Makefiles and Xcode project files. On Windows, it will generate Makefiles (for nmake) and Visual Studio project files.

All of the "smarts" stay in the CMake files, so there's just one authoritative source of build knowledge. This means that people can use the development environment they prefer without having to worry so much about breaking other people's builds. Because CMake files are plain text, merging is easy, as is maintaining experimental patches.

CMake tells your build system how to rebuild its input files when it detects changes to CMake's configuration files. This means that you only need to run cmake once. After that, make or your IDE should keep the CMake files and its own project files in sync for you.

Performing a build with CMake

Our builds are now managed one layer further out then CMake, using Autobuild; starting there is recommended.

Per platform build instructions for CMake-based builds of the Second Life viewer are available for these platforms:


Modifying CMake Files

What to modify

'TODO - discuss structure of CMake files

Patching guidelines

We welcome your patches! We can't test on every permutation of platform, compiler, IDE, and libraries, so if you have problems that you can fix, please contribute your fixes and we'll do our best to ensure that you only have to fix problems once.

If you're sending patches in, please follow a few simple guidelines:

  • Follow the existing coding style in the CMake files. I don't like code shouting at me, so prefer lowercase letters.
  • One logical change per patch.
  • Use spaces for indentation, not tabs.

See Submitting patches for more details.

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