Android NDK 开发之 CMake 编译 libpng

1. libpng是什么?
   专门对png进行读写,并且要与zlib同时使用

2. Android 使用cmake编译libpng项目地址:
   https://github.com/kingdawin/libpng-android
   这个项目只需要libpng代码,而不用下载zlib，只需在cmake中关联Android系统的zlib库。由于Android Bitmap解压也用到libpng库，所以系统自身带有zlib。

3. cmake配置相关知识

• 库与库如何关联
  使用target_link_libraries()，在里面加入你需要关联的库即可

# png库与zlib关联
target_link_libraries( ${project_name} PUBLIC ZLIB::ZLIB )

• 如何添加多个库
  使用add_library

add_library( 
#库名
${project_name} 
#代码路径
${sources} 
${headers} )

项目CMakeList.txt文件说明

cmake_minimum_required( VERSION 3.6 )
# png库名
set( project_name png )
project( ${project_name} )

if( MSVC )
    add_definitions(/MP)
endif()
#jni代码路径，根据你实际路径修改
set( source_dir ${CMAKE_CURRENT_SOURCE_DIR}/jni )
#头文件路径
set( headers
    ${source_dir}/pnginfo.h
    ${source_dir}/config.h
    ${source_dir}/png.h
    ${source_dir}/pngconf.h
    ${source_dir}/pngdebug.h
    ${source_dir}/pnglibconf.h
    ${source_dir}/pngprefix.h
    ${source_dir}/pngpriv.h
    ${source_dir}/pngstruct.h
)
# c文件路径
set( sources
    ${source_dir}/arm/arm_init.c
    ${source_dir}/arm/filter_neon.S
    ${source_dir}/arm/filter_neon_intrinsics.c
    ${source_dir}/png.c
    ${source_dir}/pngerror.c
    ${source_dir}/pngget.c
    ${source_dir}/pngmem.c
    ${source_dir}/pngpread.c
    ${source_dir}/pngread.c
    ${source_dir}/pngrio.c
    ${source_dir}/pngrtran.c
    ${source_dir}/pngrutil.c
    ${source_dir}/pngset.c
    ${source_dir}/pngtest.c
    ${source_dir}/pngtrans.c
    ${source_dir}/pngwio.c
    ${source_dir}/pngwrite.c
    ${source_dir}/pngwtran.c
    ${source_dir}/pngwutil.c
)
# 链接系统的zlib库
find_package( zlib REQUIRED )

# If you want a shared library instead of static, specify the BUILD_SHARED_LIBS
# variable (which is a built-in CMake option).
# 添加libpng库
add_library( ${project_name} ${sources} ${headers} )
# png库与zlib关联
target_link_libraries( ${project_name} PUBLIC ZLIB::ZLIB )
target_include_directories( ${project_name} PUBLIC
    $<BUILD_INTERFACE:${source_dir}>
    $<INSTALL_INTERFACE:include>
)
#使用add_library可以添加多个库，比如自己定义一个native-jni
#native-jni要使用png lib，只要将png lib关联即可在native-jni代码文件用
# #include<png.h>引用相关函数
add_library( 
#你的库名
native-jni 
#填你的c/c++代码路径
${sources} 
${headers} )

#下面的配置用来安装，可以删除
############################################################
## INSTALL
############################################################

include( CMakePackageConfigHelpers )

set( PNG_VERSION 1.6.29 )
set( PNG_EXPORT_DIR share/png-${PNG_VERSION}/cmake )
set( PNG_EXPORT_NAME png-export )

install( TARGETS png EXPORT ${PNG_EXPORT_NAME}
    RUNTIME DESTINATION bin
    LIBRARY DESTINATION lib
    ARCHIVE DESTINATION lib
    INCLUDES DESTINATION include
)

install( FILES ${headers} DESTINATION include )
install( EXPORT ${PNG_EXPORT_NAME} DESTINATION ${PNG_EXPORT_DIR} )

configure_file( png-config.cmake.in png-config.cmake @ONLY )

write_basic_package_version_file(
    png-config-version.cmake
    VERSION ${PNG_VERSION}
    COMPATIBILITY AnyNewerVersion
)

install(
    FILES
        ${CMAKE_CURRENT_BINARY_DIR}/png-config.cmake
        ${CMAKE_CURRENT_BINARY_DIR}/png-config-version.cmake
    DESTINATION ${PNG_EXPORT_DIR}
)

4.NDK环境配置
1）下载LLDB,NDK,CMake
as中打开sdk下载，选择SDK Tools,勾选LLDB任意版本和NDK

2）设置as的NDK路径

5.在已有的项目添加Cmake文件，并与项目关联