1. 概论
在连续构建了zlib、libpng、libjpeg、libtiff、giflib以及freetype这几个库之后，接下来我们就要来一个大的，构建OpenSceneGraph这样大型库。OpenSceneGraph（简称 OSG）是一个高性能、跨平台的三维图形应用程序框架，广泛应用于科学可视化、模拟仿真、游戏开发等领域。理论上来说，上述几个库不是OSG的必须依赖库，但是将它们作为依赖库构建，OSG的功能就更完整。
2. 构建过程
构建OSG库的关键指令如下所示：
# 配置CMake
cmake .. -G "$Generator" -A x64 `-DCMAKE_BUILD_TYPE=RelWithDebInfo `-DCMAKE_PREFIX_PATH="$InstallDir" `-DCMAKE_INSTALL_PREFIX="$InstallDir" `-DGIFLIB_LIBRARY="$InstallDir/lib/giflib.lib" `-DBUILD_OSG_APPLICATIONS=ON `-DBUILD_OSG_EXAMPLES=OFF `-DBUILD_OSG_DEPRECATED_SERIALIZERS=OFF `-DCMAKE_RELWITHDEBINFO_POSTFIX=""# 构建阶段，指定构建类型
cmake --build . --config RelWithDebInfo -- /m:8# 安装阶段，指定构建类型和安装目标
cmake --build . --config RelWithDebInfo --target install
再次强调一遍，如果要优先找到提前编译好的依赖库，就需要设置CMAKE_PREFIX_PATH变量。我们把所有的库都安装到同一个目录中并设置成CMAKE_PREFIX_PATH变量，这样在构建新的依赖库的时候，CMake就能准确查找到相关的依赖库。不过，也会出现少数查找不到的情况，这里的GIFLIB就没有查找到，因此我们手动设置GIFLIB_LIBRARY。
其余的几个OSG提供的自定义构建选项中：
- BUILD_OSG_APPLICATIONS表示是否构建基于OSG的可执行程序，例如osgviewer、osgconv等。这样的应用工具还是非常实用的，推荐还是进行构建。
- BUILD_OSG_EXAMPLES表示是否构建示例程序，像这样的构建选项，为了加快构建速度一般不用进行构建。
- BUILD_OSG_DEPRECATED_SERIALIZERS看到这个DEPRECATED字眼就不用参与进行构建了，反正也是非必须项。
- CMAKE_RELWITHDEBINFO_POSTFIX表示是否给RelWithDebInfo方式编译的结果增加后缀，默认会增加后缀“rd”，这里将其设置为空。
3. 经验总结
构建像OSG这样的大型程序库，最好多看看CMake配置完成后的输出信息，例如这里的输出信息如下所示：
CMake Deprecation Warning at CMakeLists.txt:16 (CMAKE_MINIMUM_REQUIRED):Compatibility with CMake < 2.8.12 will be removed from a future version ofCMake.Update the VERSION argument <min> value or use a ...<max> suffix to tellCMake that the project does not need compatibility with older versions.-- Selecting Windows SDK version 10.0.22000.0 to target Windows 10.0.22631.
-- Could NOT find EGL (missing: EGL_LIBRARY EGL_INCLUDE_DIR)
-- Checking windows version...
-- 64 bit architecture detected
-- Could NOT find Jasper (missing: JASPER_LIBRARIES JASPER_INCLUDE_DIR)
-- Could NOT find LibXml2 (missing: LIBXML2_INCLUDE_DIR)
CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (GTA). This can lead toproblems in calling code that expects `find_package` result variables(e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindGTA.cmake:11 (INCLUDE)CMakeLists.txt:751 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (GTA). This can lead toproblems in calling code that expects `find_package` result variables(e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindGTA.cmake:15 (INCLUDE)CMakeLists.txt:751 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.-- Checking for module 'gta'
-- No package 'gta' found
-- Trying to find DCMTK expecting DCMTKConfig.cmake
-- Trying to find DCMTK expecting DCMTKConfig.cmake - failed
-- Trying to find DCMTK relying on FindDCMTK.cmake
-- Please set DCMTK_DIR and re-run configure (missing: DCMTK_config_INCLUDE_DIR DCMTK_dcmdata_INCLUDE_DIR DCMTK_dcmimage_INCLUDE_DIR DCMTK_dcmimgle_INCLUDE_DIR DCMTK_dcmjpeg_INCLUDE_DIR DCMTK_dcmjpls_INCLUDE_DIR DCMTK_dcmnet_INCLUDE_DIR DCMTK_dcmpstat_INCLUDE_DIR DCMTK_dcmqrdb_INCLUDE_DIR DCMTK_dcmsign_INCLUDE_DIR DCMTK_dcmsr_INCLUDE_DIR DCMTK_dcmtls_INCLUDE_DIR DCMTK_ofstd_INCLUDE_DIR DCMTK_oflog_INCLUDE_DIR)
-- Could NOT find GStreamer (missing: GSTREAMER_INCLUDE_DIRS GSTREAMER_LIBRARIES GSTREAMER_VERSION GSTREAMER_BASE_INCLUDE_DIRS GSTREAMER_BASE_LIBRARIES GSTREAMER_APP_INCLUDE_DIRS GSTREAMER_APP_LIBRARIES GSTREAMER_PBUTILS_INCLUDE_DIRS GSTREAMER_PBUTILS_LIBRARIES)
-- Could NOT find SDL2 (missing: SDL2_LIBRARY SDL2_INCLUDE_DIR)
-- Could NOT find SDL (missing: SDL_LIBRARY SDL_INCLUDE_DIR)
CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (Poppler-glib). This canlead to problems in calling code that expects `find_package` resultvariables (e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindPoppler-glib.cmake:2 (INCLUDE)CMakeLists.txt:761 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (Poppler-glib). This canlead to problems in calling code that expects `find_package` resultvariables (e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindPoppler-glib.cmake:6 (INCLUDE)CMakeLists.txt:761 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.-- Checking for module 'cairo'
-- No package 'cairo' found
-- Checking for module 'poppler-glib'
-- No package 'poppler-glib' found
CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (RSVG). This can lead toproblems in calling code that expects `find_package` result variables(e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindRSVG.cmake:2 (INCLUDE)CMakeLists.txt:762 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (RSVG). This can lead toproblems in calling code that expects `find_package` result variables(e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindRSVG.cmake:6 (INCLUDE)CMakeLists.txt:762 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.-- Checking for module 'librsvg-2.0>=2.35'
-- No package 'librsvg-2.0' found
-- Checking for module 'cairo'
-- No package 'cairo' found
CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (GtkGl). This can lead toproblems in calling code that expects `find_package` result variables(e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindGtkGl.cmake:2 (INCLUDE)CMakeLists.txt:763 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/FindPackageHandleStandardArgs.cmake:438 (message):The package name passed to `find_package_handle_standard_args` (PkgConfig)does not match the name of the calling package (GtkGl). This can lead toproblems in calling code that expects `find_package` result variables(e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):C:/Program Files/CMake/share/cmake-3.26/Modules/FindPkgConfig.cmake:99 (find_package_handle_standard_args)CMakeModules/FindGtkGl.cmake:6 (INCLUDE)CMakeLists.txt:763 (FIND_PACKAGE)
This warning is for project developers. Use -Wno-dev to suppress it.-- Checking for module 'gtk+-2.0'
-- No package 'gtk+-2.0' found
-- Checking for module 'gtkglext-win32-1.0'
-- No package 'gtkglext-win32-1.0' found
-- Could NOT find Fontconfig (missing: FONTCONFIG_LIBRARY FONTCONFIG_INCLUDE_DIR)
-- osgText will not be linked with FontConfig library
CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.26/Modules/Documentation.cmake:30 (message):Policy CMP0106 is not set: The Documentation module is removed. Run "cmake--help-policy CMP0106" for policy details. Use the cmake_policy command toset the policy and suppress this warning.Documentation.cmake is VTK-specific code and should not be used in non-VTKprojects. This logic in this module is best shipped with the project usingit rather than with CMake.
Call Stack (most recent call first):CMakeLists.txt:1162 (INCLUDE)
This warning is for project developers. Use -Wno-dev to suppress it.-- The following OPTIONAL packages have been found:* OpenGL* Freetype* FBX* GDAL* CURL* GIFLIB* JPEG* ZLIB* PNG* TIFF* Threads-- The following OPTIONAL packages have not been found:* EGL* ilmbase* Inventor* Jasper* OpenEXR* OpenCascade* LibXml2* COLLADA* GTA* LibVNCServer* DCMTK* FFmpeg* GStreamer* GLIB* DirectShow* SDL2* SDL* Poppler-glib* RSVG* RSVG* GtkGl* DirectInput* GtkGl* DirectInput* NVTT* NVTT* ZeroConf* LIBLAS* ZeroConf* LIBLAS* QuickTime* LIBLAS* QuickTime* QuickTime* Fontconfig-- Configuring done (3.5s)
-- Generating done (15.6s)
-- Build files have been written to: C:/Github/BuildCppDependency/Windows/OpenSceneGraph-OpenSceneGraph-3.6.5/build
看起来非常的繁杂，但是其实没什么内容，只要是在说有的依赖库找不到，有的依赖库找到了。最后还把找到的依赖库和没找到的依赖库都列出来了。关于这一点，我们只需要重点关心我们需要的依赖库是否识别成功了即可，以为有的大型库的依赖项非常多，不太可能一次性就把完整的依赖项准备好。
除此之外，还可以看看程序库提供的自定义构建选项，暂时用不到的暂时设为OFF不进行构建了，例如一些测试程序或者案例程序。CMake提供的功能非常强大，有的功能还会远程拉取代码，这个时候往往会因为国内网速的原因导致终端构建配置。不过，提供这种功能的模块往往是非必须的构建选项，可以找一找将其取消掉，在重新进行构建。
总之，多看看的构建配置的输出信息和选项，熟能生巧，有了经验以后就能又快又好地构建依赖库了。