@ 解说：

@ 1. in-source 编译就是：不新建build文件夹。那么所有CMAKE生成的东西就都堆在

@ sources 所在的路径下，这不是很混乱吗。所以禁止。

@ 2. 合理的 cmake 操作：

@ mkdir build

@ cd build

@ cmake ..

@ build/.. 就是 ${CMAKE_SOURCE_DIR}, ..表示向外一层目录。

@ build 就是 ${CMAKE_BINARY_DIR}

@ 3. STREQUAL 用于比较字符串

@ 4. message() 输出

if(" ${CMAKE_SOURCE_DIR}" STREQUAL " ${CMAKE_BINARY_DIR}")
message(FATAL_ERROR "
FATAL: In-source builds are not allowed.
You should create a separate directory for build files.
")
endif()

@ 解说：

@ include 添加xx.cmake模块，或者CMakeLists.txt

include(cmake/OpenCVMinDepVersions.cmake)

@ 解说：

@ MATCHes: 表示前面的字符串是否匹配后面的正则表达式。

@ 不是很明白，但是应该是做数据检查。有点相当于 ==

@ AND 是关系操作符，与

@ cmake_minimum_required：设置cmake版本要求

@ CMAKE_SYSTEM_NAME 等：是系统的变量。看blog说明

if(CMAKE_GENERATOR MATCHES Xcode AND XCODE_VERSION VERSION_GREATER 4.3)
cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
elseif(CMAKE_SYSTEM_NAME MATCHES WindowsPhone OR CMAKE_SYSTEM_NAME MATCHES WindowsStore)
cmake_minimum_required(VERSION 3.1 FATAL_ERROR)
#Required to resolve linker error issues due to incompatibility with CMake v3.0+ policies.
#CMake fails to find _fseeko() which leads to subsequent linker error.
#See details here: http://www.cmake.org/Wiki/CMake/Policies
cmake_policy(VERSION 2.8)
else()
cmake_minimum_required(VERSION "${MIN_VER_CMAKE}" FATAL_ERROR)
endif()

**** 节选 ****

@ 解说：

@ OR 是关系操作符，或

if(CMAKE_SYSTEM_NAME MATCHES WindowsPhone OR CMAKE_SYSTEM_NAME MATCHES WindowsStore)
set(WINRT TRUE)
endif(CMAKE_SYSTEM_NAME MATCHES WindowsPhone OR CMAKE_SYSTEM_NAME MATCHES WindowsStore)

if(WINRT)
add_definitions(-DWINRT -DNO_GETENV)

# Making definitions available to other configurations and
# to filter dependency restrictions at compile time.
if(CMAKE_SYSTEM_NAME MATCHES WindowsPhone)
set(WINRT_PHONE TRUE)
add_definitions(-DWINRT_PHONE)
elseif(CMAKE_SYSTEM_NAME MATCHES WindowsStore)
set(WINRT_STORE TRUE)
add_definitions(-DWINRT_STORE)
endif()

if(CMAKE_SYSTEM_VERSION MATCHES 10)
set(WINRT_10 TRUE)
add_definitions(-DWINRT_10)
elseif(CMAKE_SYSTEM_VERSION MATCHES 8.1)
set(WINRT_8_1 TRUE)
add_definitions(-DWINRT_8_1)
elseif(CMAKE_SYSTEM_VERSION MATCHES 8.0)
set(WINRT_8_0 TRUE)
add_definitions(-DWINRT_8_0)
endif()
endif()

include(cmake/OpenCVUtils.cmake)

must go before the project command

@ 解说：

@ ocv_update 函数定义在 cmake/OpenCVUtils.cmake 这个组件中，可以用Notepad++打开看看。

ocv_update(CMAKE_CONFIGURATION_TYPES "Debug;Release" CACHE STRING "Configs" FORCE)
if(DEFINED CMAKE_BUILD_TYPE)
set_property( CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS ${CMAKE_CONFIGURATION_TYPES} )
endif()