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Android Studio CMake使用笔记

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1. 安装cmake以及ndk

工具栏： Tools–>SDK Manager–>Android SDK

选择SDK Tools，选中NDK 以及 CMake 下载安装

 图：

2. 新建工程

    修改build.gradle

defaultConfig {
    minSdk 28
    targetSdk 32
    versionCode 1
    versionName "1.0"

    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    consumerProguardFiles "consumer-rules.pro"

    externalNativeBuild {
        cmake {
            // Passes optional arguments to CMake.
            arguments "-DANDROID_ARM_NEON=TRUE", "-DANDROID_TOOLCHAIN=clang"
            // Sets a flag to enable format macro constants for the C compiler.
            //cFlags "-D__STDC_FORMAT_MACROS"
            // Sets optional flags for the C++ compiler.
            cppFlags "-fexceptions", "-frtti"
            //仅生成单个平台
            //abiFilters "armeabi-v7a"//,"arm64-v8a" //"x86", "x86_64"
        }
    }

    //生成多个平台共享库
    ndk{
        abiFilters "armeabi-v7a","arm64-v8a" //"x86", "x86_64"
    }  
    sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }
}
externalNativeBuild {
    cmake {
        path "src/main/cpp/CMakeLists.txt"
        version "3.10.2"
    }
}

3. CMakeLists.txt 修改要点

# 设置本地库编译所需的最小cmake版本
cmake_minimum_required(VERSION 3.10.2)

# 本地native项目名
project("ffmpeg")

## 配置 ##
# 设置本地库根目录
set(native_root_dir ${CMAKE_CURRENT_LIST_DIR})
# 设置本地库源码路径
set(native_source_dir ${native_root_dir}/native)
# 设置第三方静态库ffmpeg路径
set(native_ffmpeg_dir ${native_root_dir}/ffmpeg/armeabi_v7a)
# 设置第三方库libyuv源码路径
set(native_yuv_dir ${native_root_dir}/libyuv)
# 设置第三方库libyuv编译资源路径
set(native_yuv_build_dir ${native_yuv_dir}/build)
# 设置第三方库libyuv头文件路径
set(native_yuv_inc_dir ${native_yuv_dir}/include)

# 设置本地库编译目标名称
set(native_lib_name "ffmpeg")
# 设置本地库编译输出路径
set(native_build_output_dir ${native_root_dir}/../../../build/intermediates/library_jni/debug/jni/${ANDROID_ABI})

## 第三方子目录libyuv配置 ##
# 构建编译文件依赖路径
file(MAKE_DIRECTORY ${native_yuv_build_dir})
# 构建添加一个子路径；添加libyuv子目录，执行子目录中的CMakeLists.txt
add_subdirectory( ${native_yuv_dir} ${native_yuv_build_dir} )
# 创建一个static库lib_yuv  直接引用${native_yuv_build_dir}/libyuv_static.a
add_library( lib_yuv STATIC IMPORTED )
set_target_properties( lib_yuv PROPERTIES IMPORTED_LOCATION
        ${native_yuv_build_dir}/libyuv_static.a )

# 指定native头文件路径
include_directories(${native_source_dir} )
# 指定libyuv头文件路径
include_directories( ${native_yuv_dir}/include )
# 指定ffmpeg静态库头文件路径
include_directories( ${native_ffmpeg_dir}/include )

# 设置native源码文件集合
set(native_source_files
    ${native_source_dir}/native_jni.cpp
)
# 用native_source_files源文件集合编译生成SHARED库
add_library(${native_lib_name} SHARED ${native_source_files} )
# 设置${native_lib_name}库编译输出路径
set_target_properties(${native_lib_name}
        PROPERTIES
        LIBRARY_OUTPUT_DIRECTORY
        "${PROJECT_SOURCE_DIR}/../jniLibs/${ANDROID_ABI}")

## import ffmpeg static lib
# 创建一个static库avcodec  直接引用${native_ffmpeg_dir}/lib/libavcodec.a
add_library( avcodec STATIC IMPORTED )
set_target_properties( avcodec PROPERTIES IMPORTED_LOCATION
        ${native_ffmpeg_dir}/lib/libavcodec.a )

# 创建一个static库avfilter  直接引用{native_ffmpeg_dir}/lib/libavfilter.a
add_library( avfilter STATIC IMPORTED )
set_target_properties( avfilter PROPERTIES IMPORTED_LOCATION
        ${native_ffmpeg_dir}/lib/libavfilter.a )

add_library( avformat STATIC IMPORTED )
set_target_properties( avformat PROPERTIES IMPORTED_LOCATION
        ${native_ffmpeg_dir}/lib/libavformat.a )

add_library( avutil STATIC IMPORTED )
set_target_properties( avutil PROPERTIES IMPORTED_LOCATION
        ${native_ffmpeg_dir}/lib/libavutil.a )

add_library( swresample STATIC IMPORTED )
set_target_properties( swresample PROPERTIES IMPORTED_LOCATION
        ${native_ffmpeg_dir}/lib/libswresample.a )

add_library( swscale STATIC IMPORTED )
set_target_properties( swscale PROPERTIES IMPORTED_LOCATION
        ${native_ffmpeg_dir}/lib/libswscale.a )

# 查找动态库log
find_library(log-lib log )
#链接所有动态库/静态库到工程ffmpeg
target_link_libraries(ffmpeg avcodec avfilter avformat avutil swresample swscale lib_yuv ${log-lib})

#set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../jniLibs/${ANDROID_ABI})
#拷贝库文件.
add_custom_command(TARGET ${native_lib_name} POST_BUILD
        COMMAND "${CMAKE_COMMAND}" -E
        copy "${native_build_output_dir}/libffmpeg.so"
        "${native_root_dir}/../../../../app/libs/libffmpeg.so"
        COMMENT "Copying ${native_lib_name} to output directory")

CMake子目录库关联路径问题：

 子目录CMakeLists.txt 匹配：

编译实际结果：

1. so输出路径 CMAKE_LIBRARY_OUTPUT_DIRECTORY 
2. .a 静态库输出路径 CMAKE_ARCHIVE_OUTPUT_DIRECTORY 
2. 获取当前编译的abi ， ANDROID_ABI 
3. 编译选项： 
CMAKE_C_FLAGS 
CMAKE_CXX_FLAGS 

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Wfatal-errors -fPIC")

CMAKE_CXX_FLAGS_DEBUG/CMAKE_CXX_FLAGS_RELEASE 
4. 子目录编译: ADD_SUBDIRECTORY  

3.2 关键语句

1). 判断语句

set(BUDEG ON)

if(BUDEG )

//do something

else()

//do something

endif()

2)常用变量

CMAKE_SOURCE_DIR ( 相当于工程根目录 ) 
this is the directory, from which cmake was started, i.e. the top level source directory

CMAKE_CURRENT_SOURCE_DIR 
this is the directory where the currently processed CMakeLists.txt is located in

PROJECT_SOURCE_DIR ( =CMAKE_SOURCE_DIR 相当于工程根目录 ) 
contains the full path to the root of your project source directory, i.e. to the nearest directory where CMakeLists.txt contains the PROJECT() command

CMAKE_PREFIX_PATH （用于找 Findxxx.cmake文件，找 库 和 头文件） 
Path used for searching by FIND_XXX(), with appropriate suffixes added.

CMAKE_INSTALL_PREFIX ( 安装目录 ) 
Install directory used by install. 
If “make install” is invoked or INSTALL is built, this directory is prepended onto all install directories. This variable defaults to /usr/local on UNIX and c:/Program Files on Windows. 
例如： cmake .. -DCMAKE_INSTALL_PREFIX=/my/paht/to/install 

3).基本指令

PROJECT(HELLO) 
指定项目名称，生成的VC项目的名称，使用${HELLO_SOURCE_DIR}表示项目根目录。

INCLUDE_DIRECTORIES 
指定头文件的搜索路径，相当于指定gcc的-I参数 
INCLUDE_DIRECTORIES(${HELLO_SOURCE_DIR}/Hello) #增加Hello为include目录

TARGET_LINK_LIBRARIES 
添加链接库，相同于指定-l参数 
TARGET_LINK_LIBRARIES(demoHello) #将可执行文件与Hello连接成最终文件demo

LINK_DIRECTORIES 
动态链接库或静态链接库的搜索路径，相当于gcc的-L参数 
LINK_DIRECTORIES(${HELLO_BINARY_DIR}/Hello)#增加Hello为link目录

ADD_DEFINITIONS 
向C/C++编译器添加-D定义，比如： 
ADD_DEFINITIONS(-DENABLE_DEBUG-DABC) 
参数之间用空格分割。如果代码中定义了:

这个代码块就会生效。如果要添加其他的编译器开关,可以通过CMAKE_C_FLAGS变量和CMAKE_CXX_FLAGS变量设置。

ADD_DEPENDENCIES* 
定义target依赖的其它target，确保在编译本target之前，其它的target已经被构建。ADD_DEPENDENCIES(target-name depend-target1 depend-target2 ...)

ADD_EXECUTABLE 
ADD_EXECUTABLE(helloDemo demo.cxx demo_b.cxx) 
指定编译，好像也可以添加.o文件，将cxx编译成可执行文件

ADD_LIBRARY 
ADD_LIBRARY(Hellohello.cxx) #将hello.cxx编译成静态库如libHello.a

ADD_SUBDIRECTORY 
ADD_SUBDIRECTORY(Hello) #包含子目录

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